SQLite

  $(TOP)\src\test3.c \
  $(TOP)\src\test4.c \
  $(TOP)\src\test5.c \
  $(TOP)\src\test6.c \
  $(TOP)\src\test8.c \
  $(TOP)\src\test9.c \
  $(TOP)\src\test_autoext.c \
  $(TOP)\src\test_async.c \
  $(TOP)\src\test_backup.c \
  $(TOP)\src\test_bestindex.c \
  $(TOP)\src\test_blob.c \
  $(TOP)\src\test_btree.c \
  $(TOP)\src\test_config.c \
  $(TOP)\src\test_delete.c \
  $(TOP)\src\test_demovfs.c \

# (non-amalgamation)
#
TESTSRC2 = \
  $(SRC00) \
  $(SRC01) \
  $(SRC07) \
  $(SRC10) \
  $(TOP)\ext\async\sqlite3async.c \
  fts5.c

# Header files used by all library source files.
#
HDR = \
   $(TOP)\src\btree.h \
   $(TOP)\src\btreeInt.h \

NOTE (2012-11-29):

The functionality implemented by this extension has been superseded
by WAL-mode.  This module is no longer supported or maintained.  The
code is retained for historical reference only.

------------------------------------------------------------------------------

Normally, when SQLite writes to a database file, it waits until the write
operation is finished before returning control to the calling application.
Since writing to the file-system is usually very slow compared with CPU
bound operations, this can be a performance bottleneck. This directory
contains an extension that causes SQLite to perform all write requests
using a separate thread running in the background. Although this does not
reduce the overall system resources (CPU, disk bandwidth etc.) at all, it
allows SQLite to return control to the caller quickly even when writing to
the database, eliminating the bottleneck.

  1. Functionality

    1.1 How it Works
    1.2 Limitations
    1.3 Locking and Concurrency

  2. Compilation and Usage

  3. Porting



1. FUNCTIONALITY

  With asynchronous I/O, write requests are handled by a separate thread
  running in the background.  This means that the thread that initiates
  a database write does not have to wait for (sometimes slow) disk I/O
  to occur.  The write seems to happen very quickly, though in reality
  it is happening at its usual slow pace in the background.

  Asynchronous I/O appears to give better responsiveness, but at a price.
  You lose the Durable property.  With the default I/O backend of SQLite,
  once a write completes, you know that the information you wrote is
  safely on disk.  With the asynchronous I/O, this is not the case.  If
  your program crashes or if a power loss occurs after the database
  write but before the asynchronous write thread has completed, then the
  database change might never make it to disk and the next user of the
  database might not see your change.

  You lose Durability with asynchronous I/O, but you still retain the
  other parts of ACID:  Atomic,  Consistent, and Isolated.  Many
  appliations get along fine without the Durablity.

  1.1 How it Works

    Asynchronous I/O works by creating a special SQLite "vfs" structure
    and registering it with sqlite3_vfs_register(). When files opened via 
    this vfs are written to (using the vfs xWrite() method), the data is not 
    written directly to disk, but is placed in the "write-queue" to be
    handled by the background thread.

    When files opened with the asynchronous vfs are read from 
    (using the vfs xRead() method), the data is read from the file on 
    disk and the write-queue, so that from the point of view of
    the vfs reader the xWrite() appears to have already completed.

    The special vfs is registered (and unregistered) by calls to the 
    API functions sqlite3async_initialize() and sqlite3async_shutdown().
    See section "Compilation and Usage" below for details.

  1.2 Limitations

    In order to gain experience with the main ideas surrounding asynchronous 
    IO, this implementation is deliberately kept simple. Additional 
    capabilities may be added in the future.

    For example, as currently implemented, if writes are happening at a 
    steady stream that exceeds the I/O capability of the background writer
    thread, the queue of pending write operations will grow without bound.
    If this goes on for long enough, the host system could run out of memory. 
    A more sophisticated module could to keep track of the quantity of 
    pending writes and stop accepting new write requests when the queue of 
    pending writes grows too large.

  1.3 Locking and Concurrency

    Multiple connections from within a single process that use this
    implementation of asynchronous IO may access a single database
    file concurrently. From the point of view of the user, if all
    connections are from within a single process, there is no difference
    between the concurrency offered by "normal" SQLite and SQLite
    using the asynchronous backend.

    If file-locking is enabled (it is enabled by default), then connections
    from multiple processes may also read and write the database file.
    However concurrency is reduced as follows:

      * When a connection using asynchronous IO begins a database
        transaction, the database is locked immediately. However the
        lock is not released until after all relevant operations
        in the write-queue have been flushed to disk. This means
        (for example) that the database may remain locked for some 
        time after a "COMMIT" or "ROLLBACK" is issued.

      * If an application using asynchronous IO executes transactions
        in quick succession, other database users may be effectively
        locked out of the database. This is because when a BEGIN
        is executed, a database lock is established immediately. But
        when the corresponding COMMIT or ROLLBACK occurs, the lock
        is not released until the relevant part of the write-queue 
        has been flushed through. As a result, if a COMMIT is followed
        by a BEGIN before the write-queue is flushed through, the database 
        is never unlocked,preventing other processes from accessing 
        the database.

    File-locking may be disabled at runtime using the sqlite3async_control()
    API (see below). This may improve performance when an NFS or other 
    network file-system, as the synchronous round-trips to the server be 
    required to establish file locks are avoided. However, if multiple 
    connections attempt to access the same database file when file-locking
    is disabled, application crashes and database corruption is a likely
    outcome.


2. COMPILATION AND USAGE

  The asynchronous IO extension consists of a single file of C code
  (sqlite3async.c), and a header file (sqlite3async.h) that defines the 
  C API used by applications to activate and control the modules 
  functionality.

  To use the asynchronous IO extension, compile sqlite3async.c as
  part of the application that uses SQLite. Then use the API defined
  in sqlite3async.h to initialize and configure the module.

  The asynchronous IO VFS API is described in detail in comments in 
  sqlite3async.h. Using the API usually consists of the following steps:

    1. Register the asynchronous IO VFS with SQLite by calling the
       sqlite3async_initialize() function.

    2. Create a background thread to perform write operations and call
       sqlite3async_run().

    3. Use the normal SQLite API to read and write to databases via 
       the asynchronous IO VFS.

  Refer to sqlite3async.h for details.


3. PORTING

  Currently the asynchronous IO extension is compatible with win32 systems
  and systems that support the pthreads interface, including Mac OSX, Linux, 
  and other varieties of Unix. 

  To port the asynchronous IO extension to another platform, the user must
  implement mutex and condition variable primitives for the new platform.
  Currently there is no externally available interface to allow this, but
  modifying the code within sqlite3async.c to include the new platforms
  concurrency primitives is relatively easy. Search within sqlite3async.c
  for the comment string "PORTING FUNCTIONS" for details. Then implement
  new versions of each of the following:

    static void async_mutex_enter(int eMutex);
    static void async_mutex_leave(int eMutex);
    static void async_cond_wait(int eCond, int eMutex);
    static void async_cond_signal(int eCond);
    static void async_sched_yield(void);

  The functionality required of each of the above functions is described
  in comments in sqlite3async.c.

/*
** 2005 December 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** $Id: sqlite3async.c,v 1.7 2009/07/18 11:52:04 danielk1977 Exp $
**
** This file contains the implementation of an asynchronous IO backend 
** for SQLite.
*/

#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_ASYNCIO)

#include "sqlite3async.h"
#include "sqlite3.h"
#include <stdarg.h>
#include <string.h>
#include <assert.h>

/* Useful macros used in several places */
#define MIN(x,y) ((x)<(y)?(x):(y))
#define MAX(x,y) ((x)>(y)?(x):(y))

#ifndef SQLITE_AMALGAMATION
/* Macro to mark parameters as unused and silence compiler warnings. */
#define UNUSED_PARAMETER(x) (void)(x)
#endif

/* Forward references */
typedef struct AsyncWrite AsyncWrite;
typedef struct AsyncFile AsyncFile;
typedef struct AsyncFileData AsyncFileData;
typedef struct AsyncFileLock AsyncFileLock;
typedef struct AsyncLock AsyncLock;

/* Enable for debugging */
#ifndef NDEBUG
#include <stdio.h>
static int sqlite3async_trace = 0;
# define ASYNC_TRACE(X) if( sqlite3async_trace ) asyncTrace X
static void asyncTrace(const char *zFormat, ...){
  char *z;
  va_list ap;
  va_start(ap, zFormat);
  z = sqlite3_vmprintf(zFormat, ap);
  va_end(ap);
  fprintf(stderr, "[%d] %s", 0 /* (int)pthread_self() */, z);
  sqlite3_free(z);
}
#else
# define ASYNC_TRACE(X)
#endif

/*
** THREAD SAFETY NOTES
**
** Basic rules:
**
**     * Both read and write access to the global write-op queue must be 
**       protected by the async.queueMutex. As are the async.ioError and
**       async.nFile variables.
**
**     * The async.pLock list and all AsyncLock and AsyncFileLock
**       structures must be protected by the async.lockMutex mutex.
**
**     * The file handles from the underlying system are not assumed to 
**       be thread safe.
**
**     * See the last two paragraphs under "The Writer Thread" for
**       an assumption to do with file-handle synchronization by the Os.
**
** Deadlock prevention:
**
**     There are three mutex used by the system: the "writer" mutex, 
**     the "queue" mutex and the "lock" mutex. Rules are:
**
**     * It is illegal to block on the writer mutex when any other mutex
**       are held, and 
**
**     * It is illegal to block on the queue mutex when the lock mutex
**       is held.
**
**     i.e. mutex's must be grabbed in the order "writer", "queue", "lock".
**
** File system operations (invoked by SQLite thread):
**
**     xOpen
**     xDelete
**     xFileExists
**
** File handle operations (invoked by SQLite thread):
**
**         asyncWrite, asyncClose, asyncTruncate, asyncSync 
**    
**     The operations above add an entry to the global write-op list. They
**     prepare the entry, acquire the async.queueMutex momentarily while
**     list pointers are  manipulated to insert the new entry, then release
**     the mutex and signal the writer thread to wake up in case it happens
**     to be asleep.
**
**    
**         asyncRead, asyncFileSize.
**
**     Read operations. Both of these read from both the underlying file
**     first then adjust their result based on pending writes in the 
**     write-op queue.   So async.queueMutex is held for the duration
**     of these operations to prevent other threads from changing the
**     queue in mid operation.
**    
**
**         asyncLock, asyncUnlock, asyncCheckReservedLock
**    
**     These primitives implement in-process locking using a hash table
**     on the file name.  Files are locked correctly for connections coming
**     from the same process.  But other processes cannot see these locks
**     and will therefore not honor them.
**
**
** The writer thread:
**
**     The async.writerMutex is used to make sure only there is only
**     a single writer thread running at a time.
**
**     Inside the writer thread is a loop that works like this:
**
**         WHILE (write-op list is not empty)
**             Do IO operation at head of write-op list
**             Remove entry from head of write-op list
**         END WHILE
**
**     The async.queueMutex is always held during the <write-op list is 
**     not empty> test, and when the entry is removed from the head
**     of the write-op list. Sometimes it is held for the interim
**     period (while the IO is performed), and sometimes it is
**     relinquished. It is relinquished if (a) the IO op is an
**     ASYNC_CLOSE or (b) when the file handle was opened, two of
**     the underlying systems handles were opened on the same
**     file-system entry.
**
**     If condition (b) above is true, then one file-handle 
**     (AsyncFile.pBaseRead) is used exclusively by sqlite threads to read the
**     file, the other (AsyncFile.pBaseWrite) by sqlite3_async_flush() 
**     threads to perform write() operations. This means that read 
**     operations are not blocked by asynchronous writes (although 
**     asynchronous writes may still be blocked by reads).
**
**     This assumes that the OS keeps two handles open on the same file
**     properly in sync. That is, any read operation that starts after a
**     write operation on the same file system entry has completed returns
**     data consistent with the write. We also assume that if one thread 
**     reads a file while another is writing it all bytes other than the
**     ones actually being written contain valid data.
**
**     If the above assumptions are not true, set the preprocessor symbol
**     SQLITE_ASYNC_TWO_FILEHANDLES to 0.
*/


#ifndef NDEBUG
# define TESTONLY( X ) X
#else
# define TESTONLY( X )
#endif

/*
** PORTING FUNCTIONS
**
** There are two definitions of the following functions. One for pthreads
** compatible systems and one for Win32. These functions isolate the OS
** specific code required by each platform.
**
** The system uses three mutexes and a single condition variable. To
** block on a mutex, async_mutex_enter() is called. The parameter passed
** to async_mutex_enter(), which must be one of ASYNC_MUTEX_LOCK,
** ASYNC_MUTEX_QUEUE or ASYNC_MUTEX_WRITER, identifies which of the three
** mutexes to lock. Similarly, to unlock a mutex, async_mutex_leave() is
** called with a parameter identifying the mutex being unlocked. Mutexes
** are not recursive - it is an error to call async_mutex_enter() to
** lock a mutex that is already locked, or to call async_mutex_leave()
** to unlock a mutex that is not currently locked.
**
** The async_cond_wait() and async_cond_signal() functions are modelled
** on the pthreads functions with similar names. The first parameter to
** both functions is always ASYNC_COND_QUEUE. When async_cond_wait()
** is called the mutex identified by the second parameter must be held.
** The mutex is unlocked, and the calling thread simultaneously begins 
** waiting for the condition variable to be signalled by another thread.
** After another thread signals the condition variable, the calling
** thread stops waiting, locks mutex eMutex and returns. The 
** async_cond_signal() function is used to signal the condition variable. 
** It is assumed that the mutex used by the thread calling async_cond_wait() 
** is held by the caller of async_cond_signal() (otherwise there would be 
** a race condition).
**
** It is guaranteed that no other thread will call async_cond_wait() when
** there is already a thread waiting on the condition variable.
**
** The async_sched_yield() function is called to suggest to the operating
** system that it would be a good time to shift the current thread off the
** CPU. The system will still work if this function is not implemented
** (it is not currently implemented for win32), but it might be marginally
** more efficient if it is.
*/
static void async_mutex_enter(int eMutex);
static void async_mutex_leave(int eMutex);
static void async_cond_wait(int eCond, int eMutex);
static void async_cond_signal(int eCond);
static void async_sched_yield(void);

/*
** There are also two definitions of the following. async_os_initialize()
** is called when the asynchronous VFS is first installed, and os_shutdown()
** is called when it is uninstalled (from within sqlite3async_shutdown()).
**
** For pthreads builds, both of these functions are no-ops. For win32,
** they provide an opportunity to initialize and finalize the required
** mutex and condition variables.
**
** If async_os_initialize() returns other than zero, then the initialization
** fails and SQLITE_ERROR is returned to the user.
*/
static int async_os_initialize(void);
static void async_os_shutdown(void);

/* Values for use as the 'eMutex' argument of the above functions. The
** integer values assigned to these constants are important for assert()
** statements that verify that mutexes are locked in the correct order.
** Specifically, it is unsafe to try to lock mutex N while holding a lock 
** on mutex M if (M<=N).
*/
#define ASYNC_MUTEX_LOCK    0
#define ASYNC_MUTEX_QUEUE   1
#define ASYNC_MUTEX_WRITER  2

/* Values for use as the 'eCond' argument of the above functions. */
#define ASYNC_COND_QUEUE    0

/*************************************************************************
** Start of OS specific code.
*/
#if SQLITE_OS_WIN || defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)

#include <windows.h>

/* The following block contains the win32 specific code. */

#define mutex_held(X) (GetCurrentThreadId()==primitives.aHolder[X])

static struct AsyncPrimitives {
  int isInit;
  DWORD aHolder[3];
  CRITICAL_SECTION aMutex[3];
  HANDLE aCond[1];
} primitives = { 0 };

static int async_os_initialize(void){
  if( !primitives.isInit ){
    primitives.aCond[0] = CreateEvent(NULL, TRUE, FALSE, 0);
    if( primitives.aCond[0]==NULL ){
      return 1;
    }
    InitializeCriticalSection(&primitives.aMutex[0]);
    InitializeCriticalSection(&primitives.aMutex[1]);
    InitializeCriticalSection(&primitives.aMutex[2]);
    primitives.isInit = 1;
  }
  return 0;
}
static void async_os_shutdown(void){
  if( primitives.isInit ){
    DeleteCriticalSection(&primitives.aMutex[0]);
    DeleteCriticalSection(&primitives.aMutex[1]);
    DeleteCriticalSection(&primitives.aMutex[2]);
    CloseHandle(primitives.aCond[0]);
    primitives.isInit = 0;
  }
}

/* The following block contains the Win32 specific code. */
static void async_mutex_enter(int eMutex){
  assert( eMutex==0 || eMutex==1 || eMutex==2 );
  assert( eMutex!=2 || (!mutex_held(0) && !mutex_held(1) && !mutex_held(2)) );
  assert( eMutex!=1 || (!mutex_held(0) && !mutex_held(1)) );
  assert( eMutex!=0 || (!mutex_held(0)) );
  EnterCriticalSection(&primitives.aMutex[eMutex]);
  TESTONLY( primitives.aHolder[eMutex] = GetCurrentThreadId(); )
}
static void async_mutex_leave(int eMutex){
  assert( eMutex==0 || eMutex==1 || eMutex==2 );
  assert( mutex_held(eMutex) );
  TESTONLY( primitives.aHolder[eMutex] = 0; )
  LeaveCriticalSection(&primitives.aMutex[eMutex]);
}
static void async_cond_wait(int eCond, int eMutex){
  ResetEvent(primitives.aCond[eCond]);
  async_mutex_leave(eMutex);
  WaitForSingleObject(primitives.aCond[eCond], INFINITE);
  async_mutex_enter(eMutex);
}
static void async_cond_signal(int eCond){
  assert( mutex_held(ASYNC_MUTEX_QUEUE) );
  SetEvent(primitives.aCond[eCond]);
}
static void async_sched_yield(void){
  Sleep(0);
}
#else

/* The following block contains the pthreads specific code. */
#include <pthread.h>
#include <sched.h>

#define mutex_held(X) pthread_equal(primitives.aHolder[X], pthread_self())

static int  async_os_initialize(void) {return 0;}
static void async_os_shutdown(void) {}

static struct AsyncPrimitives {
  pthread_mutex_t aMutex[3];
  pthread_cond_t aCond[1];
  pthread_t aHolder[3];
} primitives = {
  { PTHREAD_MUTEX_INITIALIZER, 
    PTHREAD_MUTEX_INITIALIZER, 
    PTHREAD_MUTEX_INITIALIZER
  } , {
    PTHREAD_COND_INITIALIZER
  } , { 0, 0, 0 }
};

static void async_mutex_enter(int eMutex){
  assert( eMutex==0 || eMutex==1 || eMutex==2 );
  assert( eMutex!=2 || (!mutex_held(0) && !mutex_held(1) && !mutex_held(2)) );
  assert( eMutex!=1 || (!mutex_held(0) && !mutex_held(1)) );
  assert( eMutex!=0 || (!mutex_held(0)) );
  pthread_mutex_lock(&primitives.aMutex[eMutex]);
  TESTONLY( primitives.aHolder[eMutex] = pthread_self(); )
}
static void async_mutex_leave(int eMutex){
  assert( eMutex==0 || eMutex==1 || eMutex==2 );
  assert( mutex_held(eMutex) );
  TESTONLY( primitives.aHolder[eMutex] = 0; )
  pthread_mutex_unlock(&primitives.aMutex[eMutex]);
}
static void async_cond_wait(int eCond, int eMutex){
  assert( eMutex==0 || eMutex==1 || eMutex==2 );
  assert( mutex_held(eMutex) );
  TESTONLY( primitives.aHolder[eMutex] = 0; )
  pthread_cond_wait(&primitives.aCond[eCond], &primitives.aMutex[eMutex]);
  TESTONLY( primitives.aHolder[eMutex] = pthread_self(); )
}
static void async_cond_signal(int eCond){
  assert( mutex_held(ASYNC_MUTEX_QUEUE) );
  pthread_cond_signal(&primitives.aCond[eCond]);
}
static void async_sched_yield(void){
  sched_yield();
}
#endif
/*
** End of OS specific code.
*************************************************************************/

#define assert_mutex_is_held(X) assert( mutex_held(X) )


#ifndef SQLITE_ASYNC_TWO_FILEHANDLES
/* #define SQLITE_ASYNC_TWO_FILEHANDLES 0 */
#define SQLITE_ASYNC_TWO_FILEHANDLES 1
#endif

/*
** State information is held in the static variable "async" defined
** as the following structure.
**
** Both async.ioError and async.nFile are protected by async.queueMutex.
*/
static struct TestAsyncStaticData {
  AsyncWrite *pQueueFirst;     /* Next write operation to be processed */
  AsyncWrite *pQueueLast;      /* Last write operation on the list */
  AsyncLock *pLock;            /* Linked list of all AsyncLock structures */
  volatile int ioDelay;        /* Extra delay between write operations */
  volatile int eHalt;          /* One of the SQLITEASYNC_HALT_XXX values */
  volatile int bLockFiles;     /* Current value of "lockfiles" parameter */
  int ioError;                 /* True if an IO error has occurred */
  int nFile;                   /* Number of open files (from sqlite pov) */
} async = { 0,0,0,0,0,1,0,0 };

/* Possible values of AsyncWrite.op */
#define ASYNC_NOOP          0
#define ASYNC_WRITE         1
#define ASYNC_SYNC          2
#define ASYNC_TRUNCATE      3
#define ASYNC_CLOSE         4
#define ASYNC_DELETE        5
#define ASYNC_OPENEXCLUSIVE 6
#define ASYNC_UNLOCK        7

/* Names of opcodes.  Used for debugging only.
** Make sure these stay in sync with the macros above!
*/
static const char *azOpcodeName[] = {
  "NOOP", "WRITE", "SYNC", "TRUNCATE", "CLOSE", "DELETE", "OPENEX", "UNLOCK"
};

/*
** Entries on the write-op queue are instances of the AsyncWrite
** structure, defined here.
**
** The interpretation of the iOffset and nByte variables varies depending 
** on the value of AsyncWrite.op:
**
** ASYNC_NOOP:
**     No values used.
**
** ASYNC_WRITE:
**     iOffset -> Offset in file to write to.
**     nByte   -> Number of bytes of data to write (pointed to by zBuf).
**
** ASYNC_SYNC:
**     nByte   -> flags to pass to sqlite3OsSync().
**
** ASYNC_TRUNCATE:
**     iOffset -> Size to truncate file to.
**     nByte   -> Unused.
**
** ASYNC_CLOSE:
**     iOffset -> Unused.
**     nByte   -> Unused.
**
** ASYNC_DELETE:
**     iOffset -> Contains the "syncDir" flag.
**     nByte   -> Number of bytes of zBuf points to (file name).
**
** ASYNC_OPENEXCLUSIVE:
**     iOffset -> Value of "delflag".
**     nByte   -> Number of bytes of zBuf points to (file name).
**
** ASYNC_UNLOCK:
**     nByte   -> Argument to sqlite3OsUnlock().
**
**
** For an ASYNC_WRITE operation, zBuf points to the data to write to the file. 
** This space is sqlite3_malloc()d along with the AsyncWrite structure in a
** single blob, so is deleted when sqlite3_free() is called on the parent 
** structure.
*/
struct AsyncWrite {
  AsyncFileData *pFileData;    /* File to write data to or sync */
  int op;                      /* One of ASYNC_xxx etc. */
  sqlite_int64 iOffset;        /* See above */
  int nByte;          /* See above */
  char *zBuf;         /* Data to write to file (or NULL if op!=ASYNC_WRITE) */
  AsyncWrite *pNext;  /* Next write operation (to any file) */
};

/*
** An instance of this structure is created for each distinct open file 
** (i.e. if two handles are opened on the one file, only one of these
** structures is allocated) and stored in the async.aLock hash table. The
** keys for async.aLock are the full pathnames of the opened files.
**
** AsyncLock.pList points to the head of a linked list of AsyncFileLock
** structures, one for each handle currently open on the file.
**
** If the opened file is not a main-database (the SQLITE_OPEN_MAIN_DB is
** not passed to the sqlite3OsOpen() call), or if async.bLockFiles is 
** false, variables AsyncLock.pFile and AsyncLock.eLock are never used. 
** Otherwise, pFile is a file handle opened on the file in question and 
** used to obtain the file-system locks required by database connections 
** within this process.
**
** See comments above the asyncLock() function for more details on 
** the implementation of database locking used by this backend.
*/
struct AsyncLock {
  char *zFile;
  int nFile;
  sqlite3_file *pFile;
  int eLock;
  AsyncFileLock *pList;
  AsyncLock *pNext;           /* Next in linked list headed by async.pLock */
};

/*
** An instance of the following structure is allocated along with each
** AsyncFileData structure (see AsyncFileData.lock), but is only used if the
** file was opened with the SQLITE_OPEN_MAIN_DB.
*/
struct AsyncFileLock {
  int eLock;                /* Internally visible lock state (sqlite pov) */
  int eAsyncLock;           /* Lock-state with write-queue unlock */
  AsyncFileLock *pNext;
};

/* 
** The AsyncFile structure is a subclass of sqlite3_file used for 
** asynchronous IO. 
**
** All of the actual data for the structure is stored in the structure
** pointed to by AsyncFile.pData, which is allocated as part of the
** sqlite3OsOpen() using sqlite3_malloc(). The reason for this is that the
** lifetime of the AsyncFile structure is ended by the caller after OsClose()
** is called, but the data in AsyncFileData may be required by the
** writer thread after that point.
*/
struct AsyncFile {
  sqlite3_io_methods *pMethod;
  AsyncFileData *pData;
};
struct AsyncFileData {
  char *zName;               /* Underlying OS filename - used for debugging */
  int nName;                 /* Number of characters in zName */
  sqlite3_file *pBaseRead;   /* Read handle to the underlying Os file */
  sqlite3_file *pBaseWrite;  /* Write handle to the underlying Os file */
  AsyncFileLock lock;        /* Lock state for this handle */
  AsyncLock *pLock;          /* AsyncLock object for this file system entry */
  AsyncWrite closeOp;        /* Preallocated close operation */
};

/*
** Add an entry to the end of the global write-op list. pWrite should point 
** to an AsyncWrite structure allocated using sqlite3_malloc().  The writer
** thread will call sqlite3_free() to free the structure after the specified
** operation has been completed.
**
** Once an AsyncWrite structure has been added to the list, it becomes the
** property of the writer thread and must not be read or modified by the
** caller.  
*/
static void addAsyncWrite(AsyncWrite *pWrite){
  /* We must hold the queue mutex in order to modify the queue pointers */
  if( pWrite->op!=ASYNC_UNLOCK ){
    async_mutex_enter(ASYNC_MUTEX_QUEUE);
  }

  /* Add the record to the end of the write-op queue */
  assert( !pWrite->pNext );
  if( async.pQueueLast ){
    assert( async.pQueueFirst );
    async.pQueueLast->pNext = pWrite;
  }else{
    async.pQueueFirst = pWrite;
  }
  async.pQueueLast = pWrite;
  ASYNC_TRACE(("PUSH %p (%s %s %d)\n", pWrite, azOpcodeName[pWrite->op],
         pWrite->pFileData ? pWrite->pFileData->zName : "-", pWrite->iOffset));

  if( pWrite->op==ASYNC_CLOSE ){
    async.nFile--;
  }

  /* The writer thread might have been idle because there was nothing
  ** on the write-op queue for it to do.  So wake it up. */
  async_cond_signal(ASYNC_COND_QUEUE);

  /* Drop the queue mutex */
  if( pWrite->op!=ASYNC_UNLOCK ){
    async_mutex_leave(ASYNC_MUTEX_QUEUE);
  }
}

/*
** Increment async.nFile in a thread-safe manner.
*/
static void incrOpenFileCount(void){
  /* We must hold the queue mutex in order to modify async.nFile */
  async_mutex_enter(ASYNC_MUTEX_QUEUE);
  if( async.nFile==0 ){
    async.ioError = SQLITE_OK;
  }
  async.nFile++;
  async_mutex_leave(ASYNC_MUTEX_QUEUE);
}

/*
** This is a utility function to allocate and populate a new AsyncWrite
** structure and insert it (via addAsyncWrite() ) into the global list.
*/
static int addNewAsyncWrite(
  AsyncFileData *pFileData, 
  int op, 
  sqlite3_int64 iOffset, 
  int nByte,
  const char *zByte
){
  AsyncWrite *p;
  if( op!=ASYNC_CLOSE && async.ioError ){
    return async.ioError;
  }
  p = sqlite3_malloc(sizeof(AsyncWrite) + (zByte?nByte:0));
  if( !p ){
    /* The upper layer does not expect operations like OsWrite() to
    ** return SQLITE_NOMEM. This is partly because under normal conditions
    ** SQLite is required to do rollback without calling malloc(). So
    ** if malloc() fails here, treat it as an I/O error. The above
    ** layer knows how to handle that.
    */
    return SQLITE_IOERR;
  }
  p->op = op;
  p->iOffset = iOffset;
  p->nByte = nByte;
  p->pFileData = pFileData;
  p->pNext = 0;
  if( zByte ){
    p->zBuf = (char *)&p[1];
    memcpy(p->zBuf, zByte, nByte);
  }else{
    p->zBuf = 0;
  }
  addAsyncWrite(p);
  return SQLITE_OK;
}

/*
** Close the file. This just adds an entry to the write-op list, the file is
** not actually closed.
*/
static int asyncClose(sqlite3_file *pFile){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;

  /* Unlock the file, if it is locked */
  async_mutex_enter(ASYNC_MUTEX_LOCK);
  p->lock.eLock = 0;
  async_mutex_leave(ASYNC_MUTEX_LOCK);

  addAsyncWrite(&p->closeOp);
  return SQLITE_OK;
}

/*
** Implementation of sqlite3OsWrite() for asynchronous files. Instead of 
** writing to the underlying file, this function adds an entry to the end of
** the global AsyncWrite list. Either SQLITE_OK or SQLITE_NOMEM may be
** returned.
*/
static int asyncWrite(
  sqlite3_file *pFile, 
  const void *pBuf, 
  int amt, 
  sqlite3_int64 iOff
){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  return addNewAsyncWrite(p, ASYNC_WRITE, iOff, amt, pBuf);
}

/*
** Read data from the file. First we read from the filesystem, then adjust 
** the contents of the buffer based on ASYNC_WRITE operations in the 
** write-op queue.
**
** This method holds the mutex from start to finish.
*/
static int asyncRead(
  sqlite3_file *pFile, 
  void *zOut, 
  int iAmt, 
  sqlite3_int64 iOffset
){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  int rc = SQLITE_OK;
  sqlite3_int64 filesize = 0;
  sqlite3_file *pBase = p->pBaseRead;
  sqlite3_int64 iAmt64 = (sqlite3_int64)iAmt;

  /* Grab the write queue mutex for the duration of the call */
  async_mutex_enter(ASYNC_MUTEX_QUEUE);

  /* If an I/O error has previously occurred in this virtual file 
  ** system, then all subsequent operations fail.
  */
  if( async.ioError!=SQLITE_OK ){
    rc = async.ioError;
    goto asyncread_out;
  }

  if( pBase->pMethods ){
    sqlite3_int64 nRead;
    rc = pBase->pMethods->xFileSize(pBase, &filesize);
    if( rc!=SQLITE_OK ){
      goto asyncread_out;
    }
    nRead = MIN(filesize - iOffset, iAmt64);
    if( nRead>0 ){
      rc = pBase->pMethods->xRead(pBase, zOut, (int)nRead, iOffset);
      ASYNC_TRACE(("READ %s %d bytes at %d\n", p->zName, nRead, iOffset));
    }
  }

  if( rc==SQLITE_OK ){
    AsyncWrite *pWrite;
    char *zName = p->zName;

    for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
      if( pWrite->op==ASYNC_WRITE && (
        (pWrite->pFileData==p) ||
        (zName && pWrite->pFileData->zName==zName)
      )){
        sqlite3_int64 nCopy;
        sqlite3_int64 nByte64 = (sqlite3_int64)pWrite->nByte;

        /* Set variable iBeginIn to the offset in buffer pWrite->zBuf[] from
        ** which data should be copied. Set iBeginOut to the offset within
        ** the output buffer to which data should be copied. If either of
        ** these offsets is a negative number, set them to 0.
        */
        sqlite3_int64 iBeginOut = (pWrite->iOffset-iOffset);
        sqlite3_int64 iBeginIn = -iBeginOut;
        if( iBeginIn<0 ) iBeginIn = 0;
        if( iBeginOut<0 ) iBeginOut = 0;

        filesize = MAX(filesize, pWrite->iOffset+nByte64);

        nCopy = MIN(nByte64-iBeginIn, iAmt64-iBeginOut);
        if( nCopy>0 ){
          memcpy(&((char *)zOut)[iBeginOut], &pWrite->zBuf[iBeginIn], (size_t)nCopy);
          ASYNC_TRACE(("OVERREAD %d bytes at %d\n", nCopy, iBeginOut+iOffset));
        }
      }
    }
  }

asyncread_out:
  async_mutex_leave(ASYNC_MUTEX_QUEUE);
  if( rc==SQLITE_OK && filesize<(iOffset+iAmt) ){
    rc = SQLITE_IOERR_SHORT_READ;
  }
  return rc;
}

/*
** Truncate the file to nByte bytes in length. This just adds an entry to 
** the write-op list, no IO actually takes place.
*/
static int asyncTruncate(sqlite3_file *pFile, sqlite3_int64 nByte){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  return addNewAsyncWrite(p, ASYNC_TRUNCATE, nByte, 0, 0);
}

/*
** Sync the file. This just adds an entry to the write-op list, the 
** sync() is done later by sqlite3_async_flush().
*/
static int asyncSync(sqlite3_file *pFile, int flags){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  return addNewAsyncWrite(p, ASYNC_SYNC, 0, flags, 0);
}

/*
** Read the size of the file. First we read the size of the file system 
** entry, then adjust for any ASYNC_WRITE or ASYNC_TRUNCATE operations 
** currently in the write-op list. 
**
** This method holds the mutex from start to finish.
*/
int asyncFileSize(sqlite3_file *pFile, sqlite3_int64 *piSize){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  int rc = SQLITE_OK;
  sqlite3_int64 s = 0;
  sqlite3_file *pBase;

  async_mutex_enter(ASYNC_MUTEX_QUEUE);

  /* Read the filesystem size from the base file. If pMethods is NULL, this
  ** means the file hasn't been opened yet. In this case all relevant data 
  ** must be in the write-op queue anyway, so we can omit reading from the
  ** file-system.
  */
  pBase = p->pBaseRead;
  if( pBase->pMethods ){
    rc = pBase->pMethods->xFileSize(pBase, &s);
  }

  if( rc==SQLITE_OK ){
    AsyncWrite *pWrite;
    for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
      if( pWrite->op==ASYNC_DELETE 
       && p->zName 
       && strcmp(p->zName, pWrite->zBuf)==0 
      ){
        s = 0;
      }else if( pWrite->pFileData && (
          (pWrite->pFileData==p) 
       || (p->zName && pWrite->pFileData->zName==p->zName) 
      )){
        switch( pWrite->op ){
          case ASYNC_WRITE:
            s = MAX(pWrite->iOffset + (sqlite3_int64)(pWrite->nByte), s);
            break;
          case ASYNC_TRUNCATE:
            s = MIN(s, pWrite->iOffset);
            break;
        }
      }
    }
    *piSize = s;
  }
  async_mutex_leave(ASYNC_MUTEX_QUEUE);
  return rc;
}

/*
** Lock or unlock the actual file-system entry.
*/
static int getFileLock(AsyncLock *pLock){
  int rc = SQLITE_OK;
  AsyncFileLock *pIter;
  int eRequired = 0;

  if( pLock->pFile ){
    for(pIter=pLock->pList; pIter; pIter=pIter->pNext){
      assert(pIter->eAsyncLock>=pIter->eLock);
      if( pIter->eAsyncLock>eRequired ){
        eRequired = pIter->eAsyncLock;
        assert(eRequired>=0 && eRequired<=SQLITE_LOCK_EXCLUSIVE);
      }
    }

    if( eRequired>pLock->eLock ){
      rc = pLock->pFile->pMethods->xLock(pLock->pFile, eRequired);
      if( rc==SQLITE_OK ){
        pLock->eLock = eRequired;
      }
    }
    else if( eRequired<pLock->eLock && eRequired<=SQLITE_LOCK_SHARED ){
      rc = pLock->pFile->pMethods->xUnlock(pLock->pFile, eRequired);
      if( rc==SQLITE_OK ){
        pLock->eLock = eRequired;
      }
    }
  }

  return rc;
}

/*
** Return the AsyncLock structure from the global async.pLock list 
** associated with the file-system entry identified by path zName 
** (a string of nName bytes). If no such structure exists, return 0.
*/
static AsyncLock *findLock(const char *zName, int nName){
  AsyncLock *p = async.pLock;
  while( p && (p->nFile!=nName || memcmp(p->zFile, zName, nName)) ){
    p = p->pNext;
  }
  return p;
}

/*
** The following two methods - asyncLock() and asyncUnlock() - are used
** to obtain and release locks on database files opened with the
** asynchronous backend.
*/
static int asyncLock(sqlite3_file *pFile, int eLock){
  int rc = SQLITE_OK;
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;

  if( p->zName ){
    async_mutex_enter(ASYNC_MUTEX_LOCK);
    if( p->lock.eLock<eLock ){
      AsyncLock *pLock = p->pLock;
      AsyncFileLock *pIter;
      assert(pLock && pLock->pList);
      for(pIter=pLock->pList; pIter; pIter=pIter->pNext){
        if( pIter!=&p->lock && (
          (eLock==SQLITE_LOCK_EXCLUSIVE && pIter->eLock>=SQLITE_LOCK_SHARED) ||
          (eLock==SQLITE_LOCK_PENDING && pIter->eLock>=SQLITE_LOCK_RESERVED) ||
          (eLock==SQLITE_LOCK_RESERVED && pIter->eLock>=SQLITE_LOCK_RESERVED) ||
          (eLock==SQLITE_LOCK_SHARED && pIter->eLock>=SQLITE_LOCK_PENDING)
        )){
          rc = SQLITE_BUSY;
        }
      }
      if( rc==SQLITE_OK ){
        p->lock.eLock = eLock;
        p->lock.eAsyncLock = MAX(p->lock.eAsyncLock, eLock);
      }
      assert(p->lock.eAsyncLock>=p->lock.eLock);
      if( rc==SQLITE_OK ){
        rc = getFileLock(pLock);
      }
    }
    async_mutex_leave(ASYNC_MUTEX_LOCK);
  }

  ASYNC_TRACE(("LOCK %d (%s) rc=%d\n", eLock, p->zName, rc));
  return rc;
}
static int asyncUnlock(sqlite3_file *pFile, int eLock){
  int rc = SQLITE_OK;
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  if( p->zName ){
    AsyncFileLock *pLock = &p->lock;
    async_mutex_enter(ASYNC_MUTEX_QUEUE);
    async_mutex_enter(ASYNC_MUTEX_LOCK);
    pLock->eLock = MIN(pLock->eLock, eLock);
    rc = addNewAsyncWrite(p, ASYNC_UNLOCK, 0, eLock, 0);
    async_mutex_leave(ASYNC_MUTEX_LOCK);
    async_mutex_leave(ASYNC_MUTEX_QUEUE);
  }
  return rc;
}

/*
** This function is called when the pager layer first opens a database file
** and is checking for a hot-journal.
*/
static int asyncCheckReservedLock(sqlite3_file *pFile, int *pResOut){
  int ret = 0;
  AsyncFileLock *pIter;
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;

  async_mutex_enter(ASYNC_MUTEX_LOCK);
  for(pIter=p->pLock->pList; pIter; pIter=pIter->pNext){
    if( pIter->eLock>=SQLITE_LOCK_RESERVED ){
      ret = 1;
      break;
    }
  }
  async_mutex_leave(ASYNC_MUTEX_LOCK);

  ASYNC_TRACE(("CHECK-LOCK %d (%s)\n", ret, p->zName));
  *pResOut = ret;
  return SQLITE_OK;
}

/* 
** sqlite3_file_control() implementation.
*/
static int asyncFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      async_mutex_enter(ASYNC_MUTEX_LOCK);
      *(int*)pArg = ((AsyncFile*)id)->pData->lock.eLock;
      async_mutex_leave(ASYNC_MUTEX_LOCK);
      return SQLITE_OK;
    }
  }
  return SQLITE_NOTFOUND;
}

/* 
** Return the device characteristics and sector-size of the device. It
** is tricky to implement these correctly, as this backend might 
** not have an open file handle at this point.
*/
static int asyncSectorSize(sqlite3_file *pFile){
  UNUSED_PARAMETER(pFile);
  return 512;
}
static int asyncDeviceCharacteristics(sqlite3_file *pFile){
  UNUSED_PARAMETER(pFile);
  return 0;
}

static int unlinkAsyncFile(AsyncFileData *pData){
  AsyncFileLock **ppIter;
  int rc = SQLITE_OK;

  if( pData->zName ){
    AsyncLock *pLock = pData->pLock;
    for(ppIter=&pLock->pList; *ppIter; ppIter=&((*ppIter)->pNext)){
      if( (*ppIter)==&pData->lock ){
        *ppIter = pData->lock.pNext;
        break;
      }
    }
    if( !pLock->pList ){
      AsyncLock **pp;
      if( pLock->pFile ){
        pLock->pFile->pMethods->xClose(pLock->pFile);
      }
      for(pp=&async.pLock; *pp!=pLock; pp=&((*pp)->pNext));
      *pp = pLock->pNext;
      sqlite3_free(pLock);
    }else{
      rc = getFileLock(pLock);
    }
  }

  return rc;
}

/*
** The parameter passed to this function is a copy of a 'flags' parameter
** passed to this modules xOpen() method. This function returns true
** if the file should be opened asynchronously, or false if it should
** be opened immediately.
**
** If the file is to be opened asynchronously, then asyncOpen() will add
** an entry to the event queue and the file will not actually be opened
** until the event is processed. Otherwise, the file is opened directly
** by the caller.
*/
static int doAsynchronousOpen(int flags){
  return (flags&SQLITE_OPEN_CREATE) && (
      (flags&SQLITE_OPEN_MAIN_JOURNAL) ||
      (flags&SQLITE_OPEN_TEMP_JOURNAL) ||
      (flags&SQLITE_OPEN_DELETEONCLOSE)
  );
}

/*
** Open a file.
*/
static int asyncOpen(
  sqlite3_vfs *pAsyncVfs,
  const char *zName,
  sqlite3_file *pFile,
  int flags,
  int *pOutFlags
){
  static sqlite3_io_methods async_methods = {
    1,                               /* iVersion */
    asyncClose,                      /* xClose */
    asyncRead,                       /* xRead */
    asyncWrite,                      /* xWrite */
    asyncTruncate,                   /* xTruncate */
    asyncSync,                       /* xSync */
    asyncFileSize,                   /* xFileSize */
    asyncLock,                       /* xLock */
    asyncUnlock,                     /* xUnlock */
    asyncCheckReservedLock,          /* xCheckReservedLock */
    asyncFileControl,                /* xFileControl */
    asyncSectorSize,                 /* xSectorSize */
    asyncDeviceCharacteristics       /* xDeviceCharacteristics */
  };

  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  AsyncFile *p = (AsyncFile *)pFile;
  int nName = 0;
  int rc = SQLITE_OK;
  int nByte;
  AsyncFileData *pData;
  AsyncLock *pLock = 0;
  char *z;
  int isAsyncOpen = doAsynchronousOpen(flags);

  /* If zName is NULL, then the upper layer is requesting an anonymous file.
  ** Otherwise, allocate enough space to make a copy of the file name (along
  ** with the second nul-terminator byte required by xOpen).
  */
  if( zName ){
    nName = (int)strlen(zName);
  }

  nByte = (
    sizeof(AsyncFileData) +        /* AsyncFileData structure */
    2 * pVfs->szOsFile +           /* AsyncFileData.pBaseRead and pBaseWrite */
    nName + 2                      /* AsyncFileData.zName */
  ); 
  z = sqlite3_malloc(nByte);
  if( !z ){
    return SQLITE_NOMEM;
  }
  memset(z, 0, nByte);
  pData = (AsyncFileData*)z;
  z += sizeof(pData[0]);
  pData->pBaseRead = (sqlite3_file*)z;
  z += pVfs->szOsFile;
  pData->pBaseWrite = (sqlite3_file*)z;
  pData->closeOp.pFileData = pData;
  pData->closeOp.op = ASYNC_CLOSE;

  if( zName ){
    z += pVfs->szOsFile;
    pData->zName = z;
    pData->nName = nName;
    memcpy(pData->zName, zName, nName);
  }

  if( !isAsyncOpen ){
    int flagsout;
    rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseRead, flags, &flagsout);
    if( rc==SQLITE_OK 
     && (flagsout&SQLITE_OPEN_READWRITE) 
     && (flags&SQLITE_OPEN_EXCLUSIVE)==0
    ){
      rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseWrite, flags, 0);
    }
    if( pOutFlags ){
      *pOutFlags = flagsout;
    }
  }

  async_mutex_enter(ASYNC_MUTEX_LOCK);

  if( zName && rc==SQLITE_OK ){
    pLock = findLock(pData->zName, pData->nName);
    if( !pLock ){
      int nByte = pVfs->szOsFile + sizeof(AsyncLock) + pData->nName + 1; 
      pLock = (AsyncLock *)sqlite3_malloc(nByte);
      if( pLock ){
        memset(pLock, 0, nByte);
        if( async.bLockFiles && (flags&SQLITE_OPEN_MAIN_DB) ){
          pLock->pFile = (sqlite3_file *)&pLock[1];
          rc = pVfs->xOpen(pVfs, pData->zName, pLock->pFile, flags, 0);
          if( rc!=SQLITE_OK ){
            sqlite3_free(pLock);
            pLock = 0;
          }
        }
        if( pLock ){
          pLock->nFile = pData->nName;
          pLock->zFile = &((char *)(&pLock[1]))[pVfs->szOsFile];
          memcpy(pLock->zFile, pData->zName, pLock->nFile);
          pLock->pNext = async.pLock;
          async.pLock = pLock;
        }
      }else{
        rc = SQLITE_NOMEM;
      }
    }
  }

  if( rc==SQLITE_OK ){
    p->pMethod = &async_methods;
    p->pData = pData;

    /* Link AsyncFileData.lock into the linked list of 
    ** AsyncFileLock structures for this file.
    */
    if( zName ){
      pData->lock.pNext = pLock->pList;
      pLock->pList = &pData->lock;
      pData->zName = pLock->zFile;
    }
  }else{
    if( pData->pBaseRead->pMethods ){
      pData->pBaseRead->pMethods->xClose(pData->pBaseRead);
    }
    if( pData->pBaseWrite->pMethods ){
      pData->pBaseWrite->pMethods->xClose(pData->pBaseWrite);
    }
    sqlite3_free(pData);
  }

  async_mutex_leave(ASYNC_MUTEX_LOCK);

  if( rc==SQLITE_OK ){
    pData->pLock = pLock;
  }

  if( rc==SQLITE_OK && isAsyncOpen ){
    rc = addNewAsyncWrite(pData, ASYNC_OPENEXCLUSIVE, (sqlite3_int64)flags,0,0);
    if( rc==SQLITE_OK ){
      if( pOutFlags ) *pOutFlags = flags;
    }else{
      async_mutex_enter(ASYNC_MUTEX_LOCK);
      unlinkAsyncFile(pData);
      async_mutex_leave(ASYNC_MUTEX_LOCK);
      sqlite3_free(pData);
    }
  }
  if( rc!=SQLITE_OK ){
    p->pMethod = 0;
  }else{
    incrOpenFileCount();
  }

  return rc;
}

/*
** Implementation of sqlite3OsDelete. Add an entry to the end of the 
** write-op queue to perform the delete.
*/
static int asyncDelete(sqlite3_vfs *pAsyncVfs, const char *z, int syncDir){
  UNUSED_PARAMETER(pAsyncVfs);
  return addNewAsyncWrite(0, ASYNC_DELETE, syncDir, (int)strlen(z)+1, z);
}

/*
** Implementation of sqlite3OsAccess. This method holds the mutex from
** start to finish.
*/
static int asyncAccess(
  sqlite3_vfs *pAsyncVfs, 
  const char *zName, 
  int flags,
  int *pResOut
){
  int rc;
  int ret;
  AsyncWrite *p;
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;

  assert(flags==SQLITE_ACCESS_READWRITE 
      || flags==SQLITE_ACCESS_READ 
      || flags==SQLITE_ACCESS_EXISTS 
  );

  async_mutex_enter(ASYNC_MUTEX_QUEUE);
  rc = pVfs->xAccess(pVfs, zName, flags, &ret);
  if( rc==SQLITE_OK && flags==SQLITE_ACCESS_EXISTS ){
    for(p=async.pQueueFirst; p; p = p->pNext){
      if( p->op==ASYNC_DELETE && 0==strcmp(p->zBuf, zName) ){
        ret = 0;
      }else if( p->op==ASYNC_OPENEXCLUSIVE 
             && p->pFileData->zName
             && 0==strcmp(p->pFileData->zName, zName) 
      ){
        ret = 1;
      }
    }
  }
  ASYNC_TRACE(("ACCESS(%s): %s = %d\n", 
    flags==SQLITE_ACCESS_READWRITE?"read-write":
    flags==SQLITE_ACCESS_READ?"read":"exists"
    , zName, ret)
  );
  async_mutex_leave(ASYNC_MUTEX_QUEUE);
  *pResOut = ret;
  return rc;
}

/*
** Fill in zPathOut with the full path to the file identified by zPath.
*/
static int asyncFullPathname(
  sqlite3_vfs *pAsyncVfs, 
  const char *zPath, 
  int nPathOut,
  char *zPathOut
){
  int rc;
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  rc = pVfs->xFullPathname(pVfs, zPath, nPathOut, zPathOut);

  /* Because of the way intra-process file locking works, this backend
  ** needs to return a canonical path. The following block assumes the
  ** file-system uses unix style paths. 
  */
  if( rc==SQLITE_OK ){
    int i, j;
    char *z = zPathOut;
    int n = (int)strlen(z);
    while( n>1 && z[n-1]=='/' ){ n--; }
    for(i=j=0; i<n; i++){
      if( z[i]=='/' ){
        if( z[i+1]=='/' ) continue;
        if( z[i+1]=='.' && i+2<n && z[i+2]=='/' ){
          i += 1;
          continue;
        }
        if( z[i+1]=='.' && i+3<n && z[i+2]=='.' && z[i+3]=='/' ){
          while( j>0 && z[j-1]!='/' ){ j--; }
          if( j>0 ){ j--; }
          i += 2;
          continue;
        }
      }
      z[j++] = z[i];
    }
    z[j] = 0;
  }

  return rc;
}
static void *asyncDlOpen(sqlite3_vfs *pAsyncVfs, const char *zPath){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  return pVfs->xDlOpen(pVfs, zPath);
}
static void asyncDlError(sqlite3_vfs *pAsyncVfs, int nByte, char *zErrMsg){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  pVfs->xDlError(pVfs, nByte, zErrMsg);
}
static void (*asyncDlSym(
  sqlite3_vfs *pAsyncVfs, 
  void *pHandle, 
  const char *zSymbol
))(void){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  return pVfs->xDlSym(pVfs, pHandle, zSymbol);
}
static void asyncDlClose(sqlite3_vfs *pAsyncVfs, void *pHandle){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  pVfs->xDlClose(pVfs, pHandle);
}
static int asyncRandomness(sqlite3_vfs *pAsyncVfs, int nByte, char *zBufOut){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  return pVfs->xRandomness(pVfs, nByte, zBufOut);
}
static int asyncSleep(sqlite3_vfs *pAsyncVfs, int nMicro){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  return pVfs->xSleep(pVfs, nMicro);
}
static int asyncCurrentTime(sqlite3_vfs *pAsyncVfs, double *pTimeOut){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
  return pVfs->xCurrentTime(pVfs, pTimeOut);
}

static sqlite3_vfs async_vfs = {
  1,                    /* iVersion */
  sizeof(AsyncFile),    /* szOsFile */
  0,                    /* mxPathname */
  0,                    /* pNext */
  SQLITEASYNC_VFSNAME,  /* zName */
  0,                    /* pAppData */
  asyncOpen,            /* xOpen */
  asyncDelete,          /* xDelete */
  asyncAccess,          /* xAccess */
  asyncFullPathname,    /* xFullPathname */
  asyncDlOpen,          /* xDlOpen */
  asyncDlError,         /* xDlError */
  asyncDlSym,           /* xDlSym */
  asyncDlClose,         /* xDlClose */
  asyncRandomness,      /* xDlError */
  asyncSleep,           /* xDlSym */
  asyncCurrentTime      /* xDlClose */
};

/* 
** This procedure runs in a separate thread, reading messages off of the
** write queue and processing them one by one.  
**
** If async.writerHaltNow is true, then this procedure exits
** after processing a single message.
**
** If async.writerHaltWhenIdle is true, then this procedure exits when
** the write queue is empty.
**
** If both of the above variables are false, this procedure runs
** indefinately, waiting for operations to be added to the write queue
** and processing them in the order in which they arrive.
**
** An artifical delay of async.ioDelay milliseconds is inserted before
** each write operation in order to simulate the effect of a slow disk.
**
** Only one instance of this procedure may be running at a time.
*/
static void asyncWriterThread(void){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)(async_vfs.pAppData);
  AsyncWrite *p = 0;
  int rc = SQLITE_OK;
  int holdingMutex = 0;

  async_mutex_enter(ASYNC_MUTEX_WRITER);

  while( async.eHalt!=SQLITEASYNC_HALT_NOW ){
    int doNotFree = 0;
    sqlite3_file *pBase = 0;

    if( !holdingMutex ){
      async_mutex_enter(ASYNC_MUTEX_QUEUE);
    }
    while( (p = async.pQueueFirst)==0 ){
      if( async.eHalt!=SQLITEASYNC_HALT_NEVER ){
        async_mutex_leave(ASYNC_MUTEX_QUEUE);
        break;
      }else{
        ASYNC_TRACE(("IDLE\n"));
        async_cond_wait(ASYNC_COND_QUEUE, ASYNC_MUTEX_QUEUE);
        ASYNC_TRACE(("WAKEUP\n"));
      }
    }
    if( p==0 ) break;
    holdingMutex = 1;

    /* Right now this thread is holding the mutex on the write-op queue.
    ** Variable 'p' points to the first entry in the write-op queue. In
    ** the general case, we hold on to the mutex for the entire body of
    ** the loop. 
    **
    ** However in the cases enumerated below, we relinquish the mutex,
    ** perform the IO, and then re-request the mutex before removing 'p' from
    ** the head of the write-op queue. The idea is to increase concurrency with
    ** sqlite threads.
    **
    **     * An ASYNC_CLOSE operation.
    **     * An ASYNC_OPENEXCLUSIVE operation. For this one, we relinquish 
    **       the mutex, call the underlying xOpenExclusive() function, then
    **       re-aquire the mutex before seting the AsyncFile.pBaseRead 
    **       variable.
    **     * ASYNC_SYNC and ASYNC_WRITE operations, if 
    **       SQLITE_ASYNC_TWO_FILEHANDLES was set at compile time and two
    **       file-handles are open for the particular file being "synced".
    */
    if( async.ioError!=SQLITE_OK && p->op!=ASYNC_CLOSE ){
      p->op = ASYNC_NOOP;
    }
    if( p->pFileData ){
      pBase = p->pFileData->pBaseWrite;
      if( 
        p->op==ASYNC_CLOSE || 
        p->op==ASYNC_OPENEXCLUSIVE ||
        (pBase->pMethods && (p->op==ASYNC_SYNC || p->op==ASYNC_WRITE) ) 
      ){
        async_mutex_leave(ASYNC_MUTEX_QUEUE);
        holdingMutex = 0;
      }
      if( !pBase->pMethods ){
        pBase = p->pFileData->pBaseRead;
      }
    }

    switch( p->op ){
      case ASYNC_NOOP:
        break;

      case ASYNC_WRITE:
        assert( pBase );
        ASYNC_TRACE(("WRITE %s %d bytes at %d\n",
                p->pFileData->zName, p->nByte, p->iOffset));
        rc = pBase->pMethods->xWrite(pBase, (void *)(p->zBuf), p->nByte, p->iOffset);
        break;

      case ASYNC_SYNC:
        assert( pBase );
        ASYNC_TRACE(("SYNC %s\n", p->pFileData->zName));
        rc = pBase->pMethods->xSync(pBase, p->nByte);
        break;

      case ASYNC_TRUNCATE:
        assert( pBase );
        ASYNC_TRACE(("TRUNCATE %s to %d bytes\n", 
                p->pFileData->zName, p->iOffset));
        rc = pBase->pMethods->xTruncate(pBase, p->iOffset);
        break;

      case ASYNC_CLOSE: {
        AsyncFileData *pData = p->pFileData;
        ASYNC_TRACE(("CLOSE %s\n", p->pFileData->zName));
        if( pData->pBaseWrite->pMethods ){
          pData->pBaseWrite->pMethods->xClose(pData->pBaseWrite);
        }
        if( pData->pBaseRead->pMethods ){
          pData->pBaseRead->pMethods->xClose(pData->pBaseRead);
        }

        /* Unlink AsyncFileData.lock from the linked list of AsyncFileLock 
        ** structures for this file. Obtain the async.lockMutex mutex 
        ** before doing so.
        */
        async_mutex_enter(ASYNC_MUTEX_LOCK);
        rc = unlinkAsyncFile(pData);
        async_mutex_leave(ASYNC_MUTEX_LOCK);

        if( !holdingMutex ){
          async_mutex_enter(ASYNC_MUTEX_QUEUE);
          holdingMutex = 1;
        }
        assert_mutex_is_held(ASYNC_MUTEX_QUEUE);
        async.pQueueFirst = p->pNext;
        sqlite3_free(pData);
        doNotFree = 1;
        break;
      }

      case ASYNC_UNLOCK: {
        AsyncWrite *pIter;
        AsyncFileData *pData = p->pFileData;
        int eLock = p->nByte;

        /* When a file is locked by SQLite using the async backend, it is 
        ** locked within the 'real' file-system synchronously. When it is
        ** unlocked, an ASYNC_UNLOCK event is added to the write-queue to
        ** unlock the file asynchronously. The design of the async backend
        ** requires that the 'real' file-system file be locked from the
        ** time that SQLite first locks it (and probably reads from it)
        ** until all asynchronous write events that were scheduled before
        ** SQLite unlocked the file have been processed.
        **
        ** This is more complex if SQLite locks and unlocks the file multiple
        ** times in quick succession. For example, if SQLite does: 
        ** 
        **   lock, write, unlock, lock, write, unlock
        **
        ** Each "lock" operation locks the file immediately. Each "write" 
        ** and "unlock" operation adds an event to the event queue. If the
        ** second "lock" operation is performed before the first "unlock"
        ** operation has been processed asynchronously, then the first
        ** "unlock" cannot be safely processed as is, since this would mean
        ** the file was unlocked when the second "write" operation is
        ** processed. To work around this, when processing an ASYNC_UNLOCK
        ** operation, SQLite:
        **
        **   1) Unlocks the file to the minimum of the argument passed to
        **      the xUnlock() call and the current lock from SQLite's point
        **      of view, and
        **
        **   2) Only unlocks the file at all if this event is the last
        **      ASYNC_UNLOCK event on this file in the write-queue.
        */ 
        assert( holdingMutex==1 );
        assert( async.pQueueFirst==p );
        for(pIter=async.pQueueFirst->pNext; pIter; pIter=pIter->pNext){
          if( pIter->pFileData==pData && pIter->op==ASYNC_UNLOCK ) break;
        }
        if( !pIter ){
          async_mutex_enter(ASYNC_MUTEX_LOCK);
          pData->lock.eAsyncLock = MIN(
              pData->lock.eAsyncLock, MAX(pData->lock.eLock, eLock)
          );
          assert(pData->lock.eAsyncLock>=pData->lock.eLock);
          rc = getFileLock(pData->pLock);
          async_mutex_leave(ASYNC_MUTEX_LOCK);
        }
        break;
      }

      case ASYNC_DELETE:
        ASYNC_TRACE(("DELETE %s\n", p->zBuf));
        rc = pVfs->xDelete(pVfs, p->zBuf, (int)p->iOffset);
        if( rc==SQLITE_IOERR_DELETE_NOENT ) rc = SQLITE_OK;
        break;

      case ASYNC_OPENEXCLUSIVE: {
        int flags = (int)p->iOffset;
        AsyncFileData *pData = p->pFileData;
        ASYNC_TRACE(("OPEN %s flags=%d\n", p->zBuf, (int)p->iOffset));
        assert(pData->pBaseRead->pMethods==0 && pData->pBaseWrite->pMethods==0);
        rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseRead, flags, 0);
        assert( holdingMutex==0 );
        async_mutex_enter(ASYNC_MUTEX_QUEUE);
        holdingMutex = 1;
        break;
      }

      default: assert(!"Illegal value for AsyncWrite.op");
    }

    /* If we didn't hang on to the mutex during the IO op, obtain it now
    ** so that the AsyncWrite structure can be safely removed from the 
    ** global write-op queue.
    */
    if( !holdingMutex ){
      async_mutex_enter(ASYNC_MUTEX_QUEUE);
      holdingMutex = 1;
    }
    /* ASYNC_TRACE(("UNLINK %p\n", p)); */
    if( p==async.pQueueLast ){
      async.pQueueLast = 0;
    }
    if( !doNotFree ){
      assert_mutex_is_held(ASYNC_MUTEX_QUEUE);
      async.pQueueFirst = p->pNext;
      sqlite3_free(p);
    }
    assert( holdingMutex );

    /* An IO error has occurred. We cannot report the error back to the
    ** connection that requested the I/O since the error happened 
    ** asynchronously.  The connection has already moved on.  There 
    ** really is nobody to report the error to.
    **
    ** The file for which the error occurred may have been a database or
    ** journal file. Regardless, none of the currently queued operations
    ** associated with the same database should now be performed. Nor should
    ** any subsequently requested IO on either a database or journal file 
    ** handle for the same database be accepted until the main database
    ** file handle has been closed and reopened.
    **
    ** Furthermore, no further IO should be queued or performed on any file
    ** handle associated with a database that may have been part of a 
    ** multi-file transaction that included the database associated with 
    ** the IO error (i.e. a database ATTACHed to the same handle at some 
    ** point in time).
    */
    if( rc!=SQLITE_OK ){
      async.ioError = rc;
    }

    if( async.ioError && !async.pQueueFirst ){
      async_mutex_enter(ASYNC_MUTEX_LOCK);
      if( 0==async.pLock ){
        async.ioError = SQLITE_OK;
      }
      async_mutex_leave(ASYNC_MUTEX_LOCK);
    }

    /* Drop the queue mutex before continuing to the next write operation
    ** in order to give other threads a chance to work with the write queue.
    */
    if( !async.pQueueFirst || !async.ioError ){
      async_mutex_leave(ASYNC_MUTEX_QUEUE);
      holdingMutex = 0;
      if( async.ioDelay>0 ){
        pVfs->xSleep(pVfs, async.ioDelay*1000);
      }else{
        async_sched_yield();
      }
    }
  }
  
  async_mutex_leave(ASYNC_MUTEX_WRITER);
  return;
}

/*
** Install the asynchronous VFS.
*/ 
int sqlite3async_initialize(const char *zParent, int isDefault){
  int rc = SQLITE_OK;
  if( async_vfs.pAppData==0 ){
    sqlite3_vfs *pParent = sqlite3_vfs_find(zParent);
    if( !pParent || async_os_initialize() ){
      rc = SQLITE_ERROR;
    }else if( SQLITE_OK!=(rc = sqlite3_vfs_register(&async_vfs, isDefault)) ){
      async_os_shutdown();
    }else{
      async_vfs.pAppData = (void *)pParent;
      async_vfs.mxPathname = ((sqlite3_vfs *)async_vfs.pAppData)->mxPathname;
    }
  }
  return rc;
}

/*
** Uninstall the asynchronous VFS.
*/
void sqlite3async_shutdown(void){
  if( async_vfs.pAppData ){
    async_os_shutdown();
    sqlite3_vfs_unregister((sqlite3_vfs *)&async_vfs);
    async_vfs.pAppData = 0;
  }
}

/*
** Process events on the write-queue.
*/
void sqlite3async_run(void){
  asyncWriterThread();
}

/*
** Control/configure the asynchronous IO system.
*/
int sqlite3async_control(int op, ...){
  int rc = SQLITE_OK;
  va_list ap;
  va_start(ap, op);
  switch( op ){
    case SQLITEASYNC_HALT: {
      int eWhen = va_arg(ap, int);
      if( eWhen!=SQLITEASYNC_HALT_NEVER
       && eWhen!=SQLITEASYNC_HALT_NOW
       && eWhen!=SQLITEASYNC_HALT_IDLE
      ){
        rc = SQLITE_MISUSE;
        break;
      }
      async.eHalt = eWhen;
      async_mutex_enter(ASYNC_MUTEX_QUEUE);
      async_cond_signal(ASYNC_COND_QUEUE);
      async_mutex_leave(ASYNC_MUTEX_QUEUE);
      break;
    }

    case SQLITEASYNC_DELAY: {
      int iDelay = va_arg(ap, int);
      if( iDelay<0 ){
        rc = SQLITE_MISUSE;
        break;
      }
      async.ioDelay = iDelay;
      break;
    }

    case SQLITEASYNC_LOCKFILES: {
      int bLock = va_arg(ap, int);
      async_mutex_enter(ASYNC_MUTEX_QUEUE);
      if( async.nFile || async.pQueueFirst ){
        async_mutex_leave(ASYNC_MUTEX_QUEUE);
        rc = SQLITE_MISUSE;
        break;
      }
      async.bLockFiles = bLock;
      async_mutex_leave(ASYNC_MUTEX_QUEUE);
      break;
    }
      
    case SQLITEASYNC_GET_HALT: {
      int *peWhen = va_arg(ap, int *);
      *peWhen = async.eHalt;
      break;
    }
    case SQLITEASYNC_GET_DELAY: {
      int *piDelay = va_arg(ap, int *);
      *piDelay = async.ioDelay;
      break;
    }
    case SQLITEASYNC_GET_LOCKFILES: {
      int *piDelay = va_arg(ap, int *);
      *piDelay = async.bLockFiles;
      break;
    }

    default:
      rc = SQLITE_ERROR;
      break;
  }
  va_end(ap);
  return rc;
}

#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_ASYNCIO) */

#ifndef __SQLITEASYNC_H_
#define __SQLITEASYNC_H_ 1

/*
** Make sure we can call this stuff from C++.
*/
#ifdef __cplusplus
extern "C" {
#endif

#define SQLITEASYNC_VFSNAME "sqlite3async"

/*
** THREAD SAFETY NOTES:
**
** Of the four API functions in this file, the following are not threadsafe:
**
**   sqlite3async_initialize()
**   sqlite3async_shutdown()
**
** Care must be taken that neither of these functions is called while 
** another thread may be calling either any sqlite3async_XXX() function
** or an sqlite3_XXX() API function related to a database handle that
** is using the asynchronous IO VFS.
**
** These functions:
**
**   sqlite3async_run()
**   sqlite3async_control()
**
** are threadsafe. It is quite safe to call either of these functions even
** if another thread may also be calling one of them or an sqlite3_XXX()
** function related to a database handle that uses the asynchronous IO VFS.
*/

/*
** Initialize the asynchronous IO VFS and register it with SQLite using
** sqlite3_vfs_register(). If the asynchronous VFS is already initialized
** and registered, this function is a no-op. The asynchronous IO VFS
** is registered as "sqlite3async".
**
** The asynchronous IO VFS does not make operating system IO requests 
** directly. Instead, it uses an existing VFS implementation for all
** required file-system operations. If the first parameter to this function
** is NULL, then the current default VFS is used for IO. If it is not
** NULL, then it must be the name of an existing VFS. In other words, the
** first argument to this function is passed to sqlite3_vfs_find() to
** locate the VFS to use for all real IO operations. This VFS is known
** as the "parent VFS".
**
** If the second parameter to this function is non-zero, then the 
** asynchronous IO VFS is registered as the default VFS for all SQLite 
** database connections within the process. Otherwise, the asynchronous IO
** VFS is only used by connections opened using sqlite3_open_v2() that
** specifically request VFS "sqlite3async".
**
** If a parent VFS cannot be located, then SQLITE_ERROR is returned.
** In the unlikely event that operating system specific initialization
** fails (win32 systems create the required critical section and event 
** objects within this function), then SQLITE_ERROR is also returned.
** Finally, if the call to sqlite3_vfs_register() returns an error, then 
** the error code is returned to the user by this function. In all three
** of these cases, intialization has failed and the asynchronous IO VFS
** is not registered with SQLite.
**
** Otherwise, if no error occurs, SQLITE_OK is returned.
*/ 
int sqlite3async_initialize(const char *zParent, int isDefault);

/*
** This function unregisters the asynchronous IO VFS using 
** sqlite3_vfs_unregister().
**
** On win32 platforms, this function also releases the small number of 
** critical section and event objects created by sqlite3async_initialize().
*/ 
void sqlite3async_shutdown(void);

/*
** This function may only be called when the asynchronous IO VFS is 
** installed (after a call to sqlite3async_initialize()). It processes
** zero or more queued write operations before returning. It is expected
** (but not required) that this function will be called by a different 
** thread than those threads that use SQLite. The "background thread"
** that performs IO.
**
** How many queued write operations are performed before returning 
** depends on the global setting configured by passing the SQLITEASYNC_HALT
** verb to sqlite3async_control() (see below for details). By default
** this function never returns - it processes all pending operations and 
** then blocks waiting for new ones.
**
** If multiple simultaneous calls are made to sqlite3async_run() from two
** or more threads, then the calls are serialized internally.
*/
void sqlite3async_run(void);

/*
** This function may only be called when the asynchronous IO VFS is 
** installed (after a call to sqlite3async_initialize()). It is used 
** to query or configure various parameters that affect the operation 
** of the asynchronous IO VFS. At present there are three parameters 
** supported:
**
**   * The "halt" parameter, which configures the circumstances under
**     which the sqlite3async_run() parameter is configured.
**
**   * The "delay" parameter. Setting the delay parameter to a non-zero
**     value causes the sqlite3async_run() function to sleep for the
**     configured number of milliseconds between each queued write 
**     operation.
**
**   * The "lockfiles" parameter. This parameter determines whether or 
**     not the asynchronous IO VFS locks the database files it operates
**     on. Disabling file locking can improve throughput.
**
** This function is always passed two arguments. When setting the value
** of a parameter, the first argument must be one of SQLITEASYNC_HALT,
** SQLITEASYNC_DELAY or SQLITEASYNC_LOCKFILES. The second argument must
** be passed the new value for the parameter as type "int".
**
** When querying the current value of a paramter, the first argument must
** be one of SQLITEASYNC_GET_HALT, GET_DELAY or GET_LOCKFILES. The second 
** argument to this function must be of type (int *). The current value
** of the queried parameter is copied to the memory pointed to by the
** second argument. For example:
**
**   int eCurrentHalt;
**   int eNewHalt = SQLITEASYNC_HALT_IDLE;
**
**   sqlite3async_control(SQLITEASYNC_HALT, eNewHalt);
**   sqlite3async_control(SQLITEASYNC_GET_HALT, &eCurrentHalt);
**   assert( eNewHalt==eCurrentHalt );
**
** See below for more detail on each configuration parameter.
**
** SQLITEASYNC_HALT:
**
**   This is used to set the value of the "halt" parameter. The second
**   argument must be one of the SQLITEASYNC_HALT_XXX symbols defined
**   below (either NEVER, IDLE and NOW).
**
**   If the parameter is set to NEVER, then calls to sqlite3async_run()
**   never return. This is the default setting. If the parameter is set
**   to IDLE, then calls to sqlite3async_run() return as soon as the
**   queue of pending write operations is empty. If the parameter is set
**   to NOW, then calls to sqlite3async_run() return as quickly as 
**   possible, without processing any pending write requests.
**
**   If an attempt is made to set this parameter to an integer value other
**   than SQLITEASYNC_HALT_NEVER, IDLE or NOW, then sqlite3async_control() 
**   returns SQLITE_MISUSE and the current value of the parameter is not 
**   modified.
**
**   Modifying the "halt" parameter affects calls to sqlite3async_run() 
**   made by other threads that are currently in progress.
**
** SQLITEASYNC_DELAY:
**
**   This is used to set the value of the "delay" parameter. If set to
**   a non-zero value, then after completing a pending write request, the
**   sqlite3async_run() function sleeps for the configured number of 
**   milliseconds.
**
**   If an attempt is made to set this parameter to a negative value,
**   sqlite3async_control() returns SQLITE_MISUSE and the current value
**   of the parameter is not modified.
**
**   Modifying the "delay" parameter affects calls to sqlite3async_run() 
**   made by other threads that are currently in progress.
**
** SQLITEASYNC_LOCKFILES:
**
**   This is used to set the value of the "lockfiles" parameter. This
**   parameter must be set to either 0 or 1. If set to 1, then the
**   asynchronous IO VFS uses the xLock() and xUnlock() methods of the
**   parent VFS to lock database files being read and/or written. If
**   the parameter is set to 0, then these locks are omitted.
**
**   This parameter may only be set when there are no open database
**   connections using the VFS and the queue of pending write requests
**   is empty. Attempting to set it when this is not true, or to set it 
**   to a value other than 0 or 1 causes sqlite3async_control() to return
**   SQLITE_MISUSE and the value of the parameter to remain unchanged.
**
**   If this parameter is set to zero, then it is only safe to access the
**   database via the asynchronous IO VFS from within a single process. If
**   while writing to the database via the asynchronous IO VFS the database
**   is also read or written from within another process, or via another
**   connection that does not use the asynchronous IO VFS within the same
**   process, the results are undefined (and may include crashes or database
**   corruption).
**
**   Alternatively, if this parameter is set to 1, then it is safe to access
**   the database from multiple connections within multiple processes using
**   either the asynchronous IO VFS or the parent VFS directly.
*/
int sqlite3async_control(int op, ...);

/*
** Values that can be used as the first argument to sqlite3async_control().
*/
#define SQLITEASYNC_HALT          1
#define SQLITEASYNC_GET_HALT      2
#define SQLITEASYNC_DELAY         3
#define SQLITEASYNC_GET_DELAY     4
#define SQLITEASYNC_LOCKFILES     5
#define SQLITEASYNC_GET_LOCKFILES 6

/*
** If the first argument to sqlite3async_control() is SQLITEASYNC_HALT,
** the second argument should be one of the following.
*/
#define SQLITEASYNC_HALT_NEVER 0       /* Never halt (default value) */
#define SQLITEASYNC_HALT_NOW   1       /* Halt as soon as possible */
#define SQLITEASYNC_HALT_IDLE  2       /* Halt when write-queue is empty */

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif        /* ifndef __SQLITEASYNC_H_ */

#
# $(CFLAGS.intree_includes) = -I... flags relevant specifically to
# this tree, including any subdirectories commonly needed for building
# various tools.
#
CFLAGS.intree_includes = \
    -I. -I$(TOP)/src -I$(TOP)/ext/rtree -I$(TOP)/ext/icu \
    -I$(TOP)/ext/fts3 -I$(TOP)/ext/async -I$(TOP)/ext/session \
    -I$(TOP)/ext/misc -I$(TOP)/ext/userauth
T.cc.sqlite += $(CFLAGS.intree_includes)

#
# $(T.cc.extension) = compiler invocation for loadable extensions.
#
T.cc.extension = $(T.compile) -I. -I$(TOP)/src -DSQLITE_CORE

  $(TOP)/src/test3.c \
  $(TOP)/src/test4.c \
  $(TOP)/src/test5.c \
  $(TOP)/src/test6.c \
  $(TOP)/src/test8.c \
  $(TOP)/src/test9.c \
  $(TOP)/src/test_autoext.c \
  $(TOP)/src/test_async.c \
  $(TOP)/src/test_backup.c \
  $(TOP)/src/test_bestindex.c \
  $(TOP)/src/test_blob.c \
  $(TOP)/src/test_btree.c \
  $(TOP)/src/test_config.c \
  $(TOP)/src/test_delete.c \
  $(TOP)/src/test_demovfs.c \

  parse.c \
  $(TOP)/ext/fts3/fts3.c \
  $(TOP)/ext/fts3/fts3_aux.c \
  $(TOP)/ext/fts3/fts3_expr.c \
  $(TOP)/ext/fts3/fts3_term.c \
  $(TOP)/ext/fts3/fts3_tokenizer.c \
  $(TOP)/ext/fts3/fts3_write.c \
  $(TOP)/ext/async/sqlite3async.c \
  $(TOP)/ext/session/sqlite3session.c \
  $(TOP)/ext/misc/stmt.c \
  fts5.c

# Header files used by all library source files.
#
HDR = \

/*
** 2005 December 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains a binding of the asynchronous IO extension interface
** (defined in ext/async/sqlite3async.h) to Tcl.
*/

#define TCL_THREADS
#include "tclsqlite.h"

#ifdef SQLITE_ENABLE_ASYNCIO

#include "sqlite3async.h"
#include "sqlite3.h"
#include <assert.h>

/* From main.c */
extern const char *sqlite3ErrName(int);


struct TestAsyncGlobal {
  int isInstalled;                     /* True when async VFS is installed */
} testasync_g = { 0 };

TCL_DECLARE_MUTEX(testasync_g_writerMutex);

/*
** sqlite3async_initialize PARENT-VFS ISDEFAULT
*/
static int SQLITE_TCLAPI testAsyncInit(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  const char *zParent;
  int isDefault;
  int rc;

  if( objc!=3 ){
    Tcl_WrongNumArgs(interp, 1, objv, "PARENT-VFS ISDEFAULT");
    return TCL_ERROR;
  }
  zParent = Tcl_GetString(objv[1]);
  if( !*zParent ) {
    zParent = 0;
  }
  if( Tcl_GetBooleanFromObj(interp, objv[2], &isDefault) ){
    return TCL_ERROR;
  }

  rc = sqlite3async_initialize(zParent, isDefault);
  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }
  return TCL_OK;
}

/*
** sqlite3async_shutdown
*/
static int SQLITE_TCLAPI testAsyncShutdown(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  sqlite3async_shutdown();
  return TCL_OK;
}

static Tcl_ThreadCreateType tclWriterThread(ClientData pIsStarted){
  Tcl_MutexLock(&testasync_g_writerMutex);
  *((int *)pIsStarted) = 1;
  sqlite3async_run();
  Tcl_MutexUnlock(&testasync_g_writerMutex);
  Tcl_ExitThread(0);
  TCL_THREAD_CREATE_RETURN;
}

/*
** sqlite3async_start
**
** Start a new writer thread.
*/
static int SQLITE_TCLAPI testAsyncStart(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  volatile int isStarted = 0;
  ClientData threadData = (ClientData)&isStarted;

  Tcl_ThreadId x;
  const int nStack = TCL_THREAD_STACK_DEFAULT;
  const int flags = TCL_THREAD_NOFLAGS;
  int rc;

  rc = Tcl_CreateThread(&x, tclWriterThread, threadData, nStack, flags);
  if( rc!=TCL_OK ){
    Tcl_AppendResult(interp, "Tcl_CreateThread() failed", 0);
    return TCL_ERROR;
  }

  while( isStarted==0 ) { /* Busy loop */ }
  return TCL_OK;
}

/*
** sqlite3async_wait
**
** Wait for the current writer thread to terminate.
**
** If the current writer thread is set to run forever then this
** command would block forever.  To prevent that, an error is returned. 
*/
static int SQLITE_TCLAPI testAsyncWait(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int eCond;
  if( objc!=1 ){
    Tcl_WrongNumArgs(interp, 1, objv, "");
    return TCL_ERROR;
  }

  sqlite3async_control(SQLITEASYNC_GET_HALT, &eCond);
  if( eCond==SQLITEASYNC_HALT_NEVER ){
    Tcl_AppendResult(interp, "would block forever", (char*)0);
    return TCL_ERROR;
  }

  Tcl_MutexLock(&testasync_g_writerMutex);
  Tcl_MutexUnlock(&testasync_g_writerMutex);
  return TCL_OK;
}

/*
** sqlite3async_control OPTION ?VALUE?
*/
static int SQLITE_TCLAPI testAsyncControl(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int rc = SQLITE_OK;
  int aeOpt[] = { SQLITEASYNC_HALT, SQLITEASYNC_DELAY, SQLITEASYNC_LOCKFILES };
  const char *azOpt[] = { "halt", "delay", "lockfiles", 0 };
  const char *az[] = { "never", "now", "idle", 0 };
  int iVal;
  int eOpt;

  if( objc!=2 && objc!=3 ){
    Tcl_WrongNumArgs(interp, 1, objv, "OPTION ?VALUE?");
    return TCL_ERROR;
  }
  if( Tcl_GetIndexFromObj(interp, objv[1], azOpt, "option", 0, &eOpt) ){
    return TCL_ERROR;
  }
  eOpt = aeOpt[eOpt];

  if( objc==3 ){
    switch( eOpt ){
      case SQLITEASYNC_HALT: {
        assert( SQLITEASYNC_HALT_NEVER==0 );
        assert( SQLITEASYNC_HALT_NOW==1 );
        assert( SQLITEASYNC_HALT_IDLE==2 );
        if( Tcl_GetIndexFromObj(interp, objv[2], az, "value", 0, &iVal) ){
          return TCL_ERROR;
        }
        break;
      }
      case SQLITEASYNC_DELAY:
        if( Tcl_GetIntFromObj(interp, objv[2], &iVal) ){
          return TCL_ERROR;
        }
        break;

      case SQLITEASYNC_LOCKFILES:
        if( Tcl_GetBooleanFromObj(interp, objv[2], &iVal) ){
          return TCL_ERROR;
        }
        break;
    }

    rc = sqlite3async_control(eOpt, iVal);
  }

  if( rc==SQLITE_OK ){
    rc = sqlite3async_control(
        eOpt==SQLITEASYNC_HALT ? SQLITEASYNC_GET_HALT :
        eOpt==SQLITEASYNC_DELAY ? SQLITEASYNC_GET_DELAY :
        SQLITEASYNC_GET_LOCKFILES, &iVal);
  }

  if( rc!=SQLITE_OK ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
    return TCL_ERROR;
  }

  if( eOpt==SQLITEASYNC_HALT ){
    Tcl_SetObjResult(interp, Tcl_NewStringObj(az[iVal], -1));
  }else{
    Tcl_SetObjResult(interp, Tcl_NewIntObj(iVal));
  }

  return TCL_OK;
}

#endif  /* SQLITE_ENABLE_ASYNCIO */

/*
** This routine registers the custom TCL commands defined in this
** module.  This should be the only procedure visible from outside
** of this module.
*/
int Sqlitetestasync_Init(Tcl_Interp *interp){
#ifdef SQLITE_ENABLE_ASYNCIO
  Tcl_CreateObjCommand(interp,"sqlite3async_start",testAsyncStart,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_wait",testAsyncWait,0,0);

  Tcl_CreateObjCommand(interp,"sqlite3async_control",testAsyncControl,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_initialize",testAsyncInit,0,0);
  Tcl_CreateObjCommand(interp,"sqlite3async_shutdown",testAsyncShutdown,0,0);
#endif  /* SQLITE_ENABLE_ASYNCIO */
  return TCL_OK;
}

  extern int Sqlitetest2_Init(Tcl_Interp*);
  extern int Sqlitetest3_Init(Tcl_Interp*);
  extern int Sqlitetest4_Init(Tcl_Interp*);
  extern int Sqlitetest5_Init(Tcl_Interp*);
  extern int Sqlitetest6_Init(Tcl_Interp*);
  extern int Sqlitetest8_Init(Tcl_Interp*);
  extern int Sqlitetest9_Init(Tcl_Interp*);
  extern int Sqlitetestasync_Init(Tcl_Interp*);
  extern int Sqlitetest_autoext_Init(Tcl_Interp*);
  extern int Sqlitetest_blob_Init(Tcl_Interp*);
  extern int Sqlitetest_demovfs_Init(Tcl_Interp *);
  extern int Sqlitetest_func_Init(Tcl_Interp*);
  extern int Sqlitetest_hexio_Init(Tcl_Interp*);
  extern int Sqlitetest_init_Init(Tcl_Interp*);
  extern int Sqlitetest_malloc_Init(Tcl_Interp*);

  Sqlitetest2_Init(interp);
  Sqlitetest3_Init(interp);
  Sqlitetest4_Init(interp);
  Sqlitetest5_Init(interp);
  Sqlitetest6_Init(interp);
  Sqlitetest8_Init(interp);
  Sqlitetest9_Init(interp);
  Sqlitetestasync_Init(interp);
  Sqlitetest_autoext_Init(interp);
  Sqlitetest_blob_Init(interp);
  Sqlitetest_demovfs_Init(interp);
  Sqlitetest_func_Init(interp);
  Sqlitetest_hexio_Init(interp);
  Sqlitetest_init_Init(interp);
  Sqlitetest_malloc_Init(interp);

#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file runs all tests.
#
# $Id: async.test,v 1.21 2009/06/05 17:09:12 drh Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {[info commands sqlite3async_initialize] eq ""} {
  # The async logic is not built into this system
  finish_test
  return
}

rename finish_test async_really_finish_test
proc finish_test {} {
  catch {db close}
  catch {db2 close}
  catch {db3 close}
}
if {[info exists G(isquick)]} { set ASYNC_SAVE_ISQUICK $G(isquick) }
set G(isquick) 1

set ASYNC_INCLUDE {
  insert.test
  insert2.test
  insert3.test
  lock.test
  lock2.test
  lock3.test
  select1.test
  select2.test
  select3.test
  select4.test
  trans.test
}

# Enable asynchronous IO.
sqlite3async_initialize "" 1

# This proc flushes the contents of the async-IO queue through to the 
# underlying VFS. A couple of the test scripts identified in $ASYNC_INCLUDE
# above contain lines like "catch flush_async_queue" in places where 
# this is required for the tests to work in async mode.
#
proc flush_async_queue {} {
  sqlite3async_control halt idle
  sqlite3async_start
  sqlite3async_wait
  sqlite3async_control halt never
}

rename do_test async_really_do_test
proc do_test {name args} {
  uplevel async_really_do_test async_io-$name $args
  flush_async_queue
}

foreach testfile [lsort -dictionary [glob $testdir/*.test]] {
  set tail [file tail $testfile]
  if {[lsearch -exact $ASYNC_INCLUDE $tail]<0} continue
  source $testfile

  # Make sure everything is flushed through. This is because [source]ing 
  # the next test file will delete the database file on disk (using
  # [delete_file]). If the asynchronous backend still has the file
  # open, it will become confused.
  #
  flush_async_queue
}

# Flush the write-queue and disable asynchronous IO. This should ensure
# all allocated memory is cleaned up.
set sqlite3async_trace 1
flush_async_queue
sqlite3async_shutdown
set sqlite3async_trace 0

rename do_test {}
rename async_really_do_test do_test
rename finish_test {}
rename async_really_finish_test finish_test

if {[info exists ASYNC_SAVE_ISQUICK]} { set G(isquick) $ASYNC_SAVE_ISQUICK }
finish_test

#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# $Id: async2.test,v 1.12 2009/04/25 08:39:15 danielk1977 Exp $


set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {
  [info commands sqlite3async_initialize]=="" ||
  [info command sqlite3_memdebug_fail]==""
} {
  # The async logic is not built into this system
  puts "Skipping async2 tests: not compiled with required features"
  finish_test
  return
}

# Enable asynchronous IO.

set setup_script {
  CREATE TABLE counter(c);
  INSERT INTO counter(c) VALUES (1);
} 

set sql_script {
  BEGIN;
    UPDATE counter SET c = 2;
    CREATE TABLE t1(a PRIMARY KEY, b, c);
    CREATE TABLE t2(a PRIMARY KEY, b, c);
  COMMIT;

  BEGIN;
    UPDATE counter SET c = 3;
    INSERT INTO t1 VALUES('abcdefghij', 'four', 'score');
    INSERT INTO t2 VALUES('klmnopqrst', 'and', 'seven');
  COMMIT;

  UPDATE counter SET c = 'FIN';
}

db close

foreach err [list ioerr malloc-transient malloc-persistent] {
  set ::go 10
  for {set n 1} {$::go} {incr n} {
    set ::sqlite_io_error_pending 0
    sqlite3_memdebug_fail -1
    forcedelete test.db test.db-journal
    sqlite3 db test.db
    execsql $::setup_script
    db close
  
    sqlite3async_initialize "" 1
    sqlite3 db test.db
    sqlite3_db_config_lookaside db 0 0 0
  
    switch -- $err {
      ioerr             { set ::sqlite_io_error_pending $n }
      malloc-persistent { sqlite3_memdebug_fail $n -repeat 1 }
      malloc-transient  { sqlite3_memdebug_fail $n -repeat 0 }
    }

    catchsql $::sql_script
    db close

    sqlite3async_control halt idle
    sqlite3async_start
    sqlite3async_wait
    sqlite3async_control halt never
    sqlite3async_shutdown

    set ::sqlite_io_error_pending 0
    sqlite3_memdebug_fail -1

    sqlite3 db test.db
    set c [db one {SELECT c FROM counter LIMIT 1}]
    switch -- $c {
      1 {
        do_test async-$err-1.1.$n {
          execsql {
            SELECT name FROM sqlite_master;
          }
        } {counter}
      }
      2 {
        do_test async-$err-1.2.$n.1 {
          execsql {
            SELECT * FROM t1;
          }
        } {}
        do_test async-$err-1.2.$n.2 {
          execsql {
            SELECT * FROM t2;
          }
        } {}
      }
      3 {
        do_test async-$err-1.3.$n.1 {
          execsql {
            SELECT * FROM t1;
          }
        } {abcdefghij four score}
        do_test async-$err-1.3.$n.2 {
          execsql {
            SELECT * FROM t2;
          }
        } {klmnopqrst and seven}
      }
      FIN {
        incr ::go -1
      }
    }
  
    db close
  }
}

catch {db close}

finish_test

# 2007 September 5
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# The focus of this file is testing the code in test_async.c.
# Specifically, it tests that the xFullPathname() method of
# of the asynchronous vfs works correctly.
#
# $Id: async3.test,v 1.5 2009/04/25 08:39:15 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

if { [info commands sqlite3async_initialize]==""  } {
  # The async logic is not built into this system
  puts "Skipping async3 tests: not compiled with required features"
  finish_test
  return
}

db close
sqlite3async_initialize "" 1
#set sqlite3async_trace 1
sqlite3async_start

set paths {
  chocolate/banana/vanilla/file.db
  chocolate//banana/vanilla/file.db
  chocolate/./banana//vanilla/file.db
  chocolate/banana/./vanilla/file.db
  chocolate/banana/../banana/vanilla/file.db
  chocolate/banana/./vanilla/extra_bit/../file.db
}

do_test async3-1.0 {
  file mkdir [file join chocolate banana vanilla]
  forcedelete chocolate/banana/vanilla/file.db
  forcedelete chocolate/banana/vanilla/file.db-journal
} {}

do_test async3-1.1 {
  sqlite3 db chocolate/banana/vanilla/file.db
  execsql {
    CREATE TABLE abc(a, b, c);
    BEGIN;
    INSERT INTO abc VALUES(1, 2, 3);
  }
} {}

set N 2
foreach p $paths {
  sqlite3 db2 $p
  do_test async3-1.$N.1 {
    execsql {SELECT * FROM abc} db2
  } {}
  do_test async3-1.$N.2 {
    catchsql {INSERT INTO abc VALUES(4, 5, 6)} db2
  } {1 {database is locked}}
  db2 close
  incr N
}

db close

sqlite3async_control halt idle
sqlite3async_wait
sqlite3async_control halt never
sqlite3async_shutdown
finish_test

# 2009 April 25
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# $Id: async4.test,v 1.4 2009/06/05 17:09:12 drh Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Do not use a codec for tests in this file, as the database file is
# manipulated directly using tcl scripts (using the [hexio_write] command).
#
do_not_use_codec

# These tests only work for Tcl version 8.5 and later on Windows (for now)
#
if {$tcl_platform(platform)=="windows"} {
  scan $::tcl_version %f vx
  if {$vx<8.5} {
    finish_test
    return
  }
}

if {[info commands sqlite3async_initialize] eq ""} {
  # The async logic is not built into this system
  finish_test
  return
}
db close

# Test layout:
#
#   async4.1.*: Test the lockfiles parameter.
#   async4.2.*: Test the delay parameter.

do_test async4.1.1 {
  sqlite3async_initialize {} 0
  sqlite3async_control lockfiles
} {1}
do_test async4.1.2 {
  sqlite3async_control lockfiles false
} {0}
do_test async4.1.3 {
  sqlite3async_control lockfiles
} {0}
do_test async4.1.4 {
  sqlite3async_control lockfiles true
} {1}

do_test async4.1.5 {
  sqlite3 db test.db -vfs sqlite3async
  execsql { CREATE TABLE t1(a, b, c) }
} {}
do_test async4.1.6 {
  list [file exists test.db] [file size test.db]
} {1 0}
do_test async4.1.7 {
  sqlite3 db2 test.db
  catchsql { CREATE TABLE t2(a, b, c) } db2
} {1 {database is locked}}
do_test async4.1.8 {
  sqlite3async_control halt idle
  sqlite3async_start
  sqlite3async_wait
} {}
do_test async4.1.9 {
  catchsql { CREATE TABLE t2(a, b, c) } db2
} {0 {}}
do_test async4.1.10 {
  list [catch {sqlite3async_control lockfiles false} msg] $msg
} {1 SQLITE_MISUSE}
do_test async4.1.11 {
  db close
  list [catch {sqlite3async_control lockfiles false} msg] $msg
} {1 SQLITE_MISUSE}
do_test async4.1.12 {
  sqlite3async_start
  sqlite3async_wait
  sqlite3async_control lockfiles false
} {0}
do_test async4.1.13 {
  sqlite3 db test.db -vfs sqlite3async
  execsql { CREATE TABLE t3(a, b, c) } db
} {}
do_test async4.1.14 {
  execsql { 
    CREATE INDEX i1 ON t2(a);
    CREATE INDEX i2 ON t1(a);
  } db2
} {}
do_test async4.1.15 {
  sqlite3async_start
  sqlite3async_wait
  hexio_write test.db 28 00000000
  execsql { pragma integrity_check } db2
} {{*** in database main ***
Page 5 is never used}}
do_test async4.1.16 {
  db close
  db2 close
  sqlite3async_start
  sqlite3async_wait
} {}
do_test async4.1.17 {
  sqlite3async_control lockfiles true
} {1}

do_test async4.2.1 {
  sqlite3async_control delay
} {0}
do_test async4.2.2 {
  sqlite3async_control delay 23
} {23}
do_test async4.2.3 {
  sqlite3async_control delay
} {23}
do_test async4.2.4 {
  sqlite3async_control delay 0
} {0}
do_test async4.2.5 {
  sqlite3 db test.db -vfs sqlite3async

  execsql { CREATE TABLE t4(a, b) }
  set T1 [lindex [time {
    sqlite3async_start
    sqlite3async_wait
  }] 0]

  sqlite3async_control delay 100
  execsql { CREATE TABLE t5(a, b) }
  set T2 [lindex [time {
    sqlite3async_start
    sqlite3async_wait
  }] 0]

  expr {($T1+1000000) < $T2}
} {1}

do_test async4.2.6 {
  sqlite3async_control delay 0
  execsql { CREATE TABLE t6(a, b) }
  set T1 [lindex [time {
    sqlite3async_start
    sqlite3async_wait
  }] 0]

  expr {($T1+1000000) < $T2}
} {1}

do_test async4.2.7 {
  list [catch { sqlite3async_control delay -1 } msg] $msg
} {1 SQLITE_MISUSE}

do_test async4.2.8 {
  db close
  sqlite3async_start
  sqlite3async_wait
} {}

finish_test

# 2009 July 19
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file tests that asynchronous IO is compatible with multi-file
# transactions.
#
# $Id: async5.test,v 1.1 2009/07/18 11:52:04 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {[info commands sqlite3async_initialize] eq ""} {
  # The async logic is not built into this system
  finish_test
  return
}

db close
forcedelete test2.db
sqlite3async_initialize "" 1
sqlite3async_control halt never
sqlite3 db test.db

do_test async5-1.1 {
  execsql {
    ATTACH 'test2.db' AS next;
    CREATE TABLE main.t1(a, b);
    CREATE TABLE next.t2(a, b);
    BEGIN;
      INSERT INTO t1 VALUES(1, 2);
      INSERT INTO t2 VALUES(3, 4);
    COMMIT;
  }
} {}
do_test async5-1.2 {
  execsql { SELECT * FROM t1 }
} {1 2}
do_test async5-1.3 {
  execsql { SELECT * FROM t2 }
} {3 4}
do_test async5-1.4 {
  execsql {
    BEGIN;
      INSERT INTO t1 VALUES('a', 'b');
      INSERT INTO t2 VALUES('c', 'd');
    COMMIT;
  }
} {}
do_test async5-1.5 {
  execsql { SELECT * FROM t1 }
} {1 2 a b}
do_test async5-1.6 {
  execsql { SELECT * FROM t2 }
} {3 4 c d}

db close

sqlite3async_control halt idle
sqlite3async_start
sqlite3async_wait
sqlite3async_control halt never
sqlite3async_shutdown
set sqlite3async_trace 0
finish_test

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Create an alternative connection to the database
#
do_test lock-1.0 {
  # Give a complex pathname to stress the path simplification logic in
  # the vxworks driver and in test_async.
  file mkdir tempdir/t1/t2
  sqlite3 db2 ./tempdir/../tempdir/t1/.//t2/../../..//test.db
  set dummy {}
} {}
do_test lock-1.1 {
  execsql {SELECT name FROM sqlite_master WHERE type='table' ORDER BY name}
} {}

  set v [catch {execsql {create}} msg]
  lappend v $msg
} {1 {incomplete input}}
do_test main-3.6 {
  catchsql {SELECT 'abc' + #9}
} {1 {near "#9": syntax error}}

# The following test-case tests the linked list code used to manage
# sqlite3_vfs structures.
if {$::tcl_platform(platform)=="unix" 
     && [info command sqlite3async_initialize]!=""} {
  ifcapable threadsafe {
    do_test main-4.1 {
      sqlite3_crash_enable 1
      sqlite3_crash_enable 0
    
      sqlite3async_initialize "" 1
      sqlite3async_shutdown
    
      sqlite3_crash_enable 1
      sqlite3async_initialize "" 1
      sqlite3_crash_enable 0
      sqlite3async_shutdown
    
      sqlite3_crash_enable 1
      sqlite3async_initialize "" 1
      sqlite3async_shutdown
      sqlite3_crash_enable 0
    
      sqlite3async_initialize "" 1
      sqlite3_crash_enable 1
      sqlite3_crash_enable 0
      sqlite3async_shutdown
    
      sqlite3async_initialize "" 1
      sqlite3_crash_enable 1
      sqlite3async_shutdown
      sqlite3_crash_enable 0
    } {}
    do_test main-4.2 {
      set rc [catch {sqlite3 db test.db -vfs crash} msg]
      list $rc $msg
    } {1 {no such vfs: crash}}
    do_test main-4.3 {
      set rc [catch {sqlite3 db test.db -vfs async} msg]
      list $rc $msg
    } {1 {no such vfs: async}}
  }
}

# Print the version number so that it can be picked up by releasetest.tcl.
#
puts [db one {SELECT 'VERSION: ' ||
                  sqlite_version() || ' ' ||
                  sqlite_source_id();}]
   
finish_test

set EXCLUDE {
  all.test
  quick.test
  misuse.test
  memleak.test
  btree2.test
  async.test
  async2.test
  trans.test
  crash.test
  autovacuum_crash.test
}
# Test files btree2.test and btree4.test don't work if the 
# SQLITE_DEFAULT_AUTOVACUUM macro is defined to true (because they depend
# on tables being allocated starting at page 2).

}
unset f

if {$::tcl_platform(platform)!="unix"} {
  set alltests [test_set $alltests -exclude crash.test crash2.test]
}
set alltests [test_set $alltests -exclude {
  all.test        async.test         quick.test  veryquick.test
  memleak.test    permutations.test  soak.test   fts3.test
  mallocAll.test  rtree.test         full.test   extraquick.test
  session.test    rbu.test
}]

set allquicktests [test_set $alltests -exclude {
  async2.test async3.test backup_ioerr.test corrupt.test
  corruptC.test crash.test crash2.test crash3.test crash4.test crash5.test
  crash6.test crash7.test delete3.test e_fts3.test fts3rnd.test
  fkey_malloc.test fuzz.test fuzz3.test fuzz_malloc.test in2.test loadext.test
  misc7.test mutex2.test onefile.test pagerfault2.test 
  savepoint4.test savepoint6.test select9.test 
  speed1.test speed1p.test speed2.test speed3.test speed4.test 
  speed4p.test sqllimits1.test tkt2686.test thread001.test thread002.test

  # Exclude test scripts that use tcl IO to access journal files or count
  # the number of fsync() calls.
  pager.test exclusive.test jrnlmode.test sync.test misc1.test 
  journal1.test conflict.test crash8.test tkt3457.test io.test
  journal3.test 8_3_names.test shmlock.test
  pendingrace.test

  pager1.test async4.test corrupt.test filefmt.test pager2.test
  corrupt5.test corruptA.test pageropt.test

  # Exclude stmt.test, which expects sub-journals to use temporary files.
  stmt.test symlink.test

  zerodamage.test

test_suite "safe_append" -description {
  Run some tests on a SAFE_APPEND file-system.
} -initialize {
  set ::G(perm:sqlite3_args) [list -vfs devsym]
  sqlite3_simulate_device -char safe_append
} -files [
  test_set $::allquicktests shared_err.test -exclude async3.test
]

# The set of tests to run on the alternative-pcache
set perm-alt-pcache-testset {
  async.test
  attach.test
  delete.test delete2.test
  index.test
  insert.test insert2.test
  join.test join2.test
  rollback.test
  select1.test select2.test

} -initialize {
  catch {db close}
  register_jt_vfs -default ""
} -shutdown {
  unregister_jt_vfs
} -files [test_set $::allquicktests -exclude {
  wal* incrvacuum.test ioerr.test corrupt4.test io.test crash8.test 
  async4.test bigfile.test backcompat.test e_wal* fstat.test mmap2.test
  pager1.test syscall.test tkt3457.test *malloc* mmap* multiplex* nolock*
  pager2.test *fault* rowal* snapshot* superlock* symlink.test
  delete_db.test shmlock.test chunksize.test
  busy2.test avfs.test external_reader.test
}]

if {[info commands register_demovfs] != ""} {

# 2009 October 19
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {[info commands sqlite3async_initialize] eq ""} {
  # The async logic is not built into this system
  finish_test
  return
}

# Create a database.
do_test tkt-94c94-1.1 {
  execsql { CREATE TABLE t1(a, b) }
} {}

# Grow the file to larger than 4096MB (2^32 bytes)
db close
if {[catch {fake_big_file 4096 [get_pwd]/test.db} msg]} {
  puts "**** Unable to create a file larger than 4096 MB. *****"
  finish_test
  return
}

# Switch to async mode.
sqlite3async_initialize "" 1
sqlite3 db test.db
sqlite3 db2 test.db

# Read from and write to the db just past the 4096MB mark.
#
do_test tkt-94c94-2.1 {
  execsql { CREATE TABLE t2(x, y) } db
} {}
do_test tkt-94c94-2.2 {
  execsql { INSERT INTO t2 VALUES(1, 2) } db2
} {}
do_test tkt-94c94-2.3 {
  execsql { SELECT * FROM t2 } db
} {1 2}
do_test tkt-94c94-2.4 {
  sqlite3async_control halt idle
  sqlite3async_start
  sqlite3async_wait
} {}
do_test tkt-94c94-2.5 {
  execsql { SELECT * FROM t2 } db
} {1 2}
do_test tkt-94c94-2.6 {
  sqlite3async_start
  sqlite3async_wait
} {}

db close
db2 close
sqlite3async_start
sqlite3async_wait
sqlite3async_control halt never
sqlite3async_shutdown

finish_test