SQLite

  }else{
    pFile->ctrlFlags |= mask;
  }
}

/* Forward declaration */
static int unixGetTempname(int nBuf, char *zBuf);
static int unixFcntlExternalReader(unixFile*, int*);

/*
** Information and control of an open file handle.
*/
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  unixFile *pFile = (unixFile*)id;
  switch( op ){

#endif
#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
    case SQLITE_FCNTL_SET_LOCKPROXYFILE:
    case SQLITE_FCNTL_GET_LOCKPROXYFILE: {
      return proxyFileControl(id,op,pArg);
    }
#endif /* SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__) */

    case SQLITE_FCNTL_EXTERNAL_READER: {
      return unixFcntlExternalReader((unixFile*)id, (int*)pArg);
    }
  }
  return SQLITE_NOTFOUND;
}

/*
** If pFd->sectorSize is non-zero when this function is called, it is a
** no-op. Otherwise, the values of pFd->sectorSize and 

};

/*
** Constants used for locking
*/
#define UNIX_SHM_BASE   ((22+SQLITE_SHM_NLOCK)*4)         /* first lock byte */
#define UNIX_SHM_DMS    (UNIX_SHM_BASE+SQLITE_SHM_NLOCK)  /* deadman switch */

/*
** Use F_GETLK to check whether or not there are any readers with open
** wal-mode transactions in other processes on database file pFile. If
** no error occurs, return SQLITE_OK and set (*piOut) to 1 if there are 
** such transactions, or 0 otherwise. If an error occurs, return an
** SQLite error code. The final value of *piOut is undefined in this
** case.
*/
static int unixFcntlExternalReader(unixFile *pFile, int *piOut){
  int rc = SQLITE_OK;
  *piOut = 0;
  if( pFile->pShm){
    unixShmNode *pShmNode = pFile->pShm->pShmNode;
    struct flock f;

    memset(&f, 0, sizeof(f));
    f.l_type = F_WRLCK;
    f.l_whence = SEEK_SET;
    f.l_start = UNIX_SHM_BASE + 3;
    f.l_len = SQLITE_SHM_NLOCK - 3;

    sqlite3_mutex_enter(pShmNode->pShmMutex);
    if( osFcntl(pShmNode->hShm, F_GETLK, &f)<0 ){
      rc = SQLITE_IOERR_LOCK;
    }else{
      *piOut = (f.l_type!=F_UNLCK);
    }
    sqlite3_mutex_leave(pShmNode->pShmMutex);
  }

  return rc;
}


/*
** Apply posix advisory locks for all bytes from ofst through ofst+n-1.
**
** Locks block if the mask is exactly UNIX_SHM_C and are non-blocking
** otherwise.
*/

**
** <li>[[SQLITE_FCNTL_CKPT_DONE]]
** The [SQLITE_FCNTL_CKPT_DONE] opcode is invoked from within a checkpoint
** in wal mode after the client has finished copying pages from the wal
** file to the database file, but before the *-shm file is updated to
** record the fact that the pages have been checkpointed.
** </ul>
**
** <li>[[SQLITE_FCNTL_EXTERNAL_READER]]
** The EXPERIMENTAL [SQLITE_FCNTL_EXTERNAL_READER] opcode is used to detect
** whether or not there is a database client in another process with a wal-mode 
** transaction open on the database or not. It is only available on unix.The
** (void*) argument passed with this file-control should be a pointer to a
** value of type (int). The integer value is set to 1 if the database is a wal
** mode database and there exists at least one client in another process that
** currently has an SQL transaction open on the database. It is set to 0 if 
** the database is not a wal-mode db, or if there is no such connection in any
** other process. This opcode cannot be used to detect transactions opened
** by clients within the current process, only within other processes.
** </ul>
*/
#define SQLITE_FCNTL_LOCKSTATE               1
#define SQLITE_FCNTL_GET_LOCKPROXYFILE       2
#define SQLITE_FCNTL_SET_LOCKPROXYFILE       3
#define SQLITE_FCNTL_LAST_ERRNO              4
#define SQLITE_FCNTL_SIZE_HINT               5
#define SQLITE_FCNTL_CHUNK_SIZE              6

#define SQLITE_FCNTL_ROLLBACK_ATOMIC_WRITE  33
#define SQLITE_FCNTL_LOCK_TIMEOUT           34
#define SQLITE_FCNTL_DATA_VERSION           35
#define SQLITE_FCNTL_SIZE_LIMIT             36
#define SQLITE_FCNTL_CKPT_DONE              37
#define SQLITE_FCNTL_RESERVE_BYTES          38
#define SQLITE_FCNTL_CKPT_START             39

#define SQLITE_FCNTL_EXTERNAL_READER        40

/* deprecated names */
#define SQLITE_GET_LOCKPROXYFILE      SQLITE_FCNTL_GET_LOCKPROXYFILE
#define SQLITE_SET_LOCKPROXYFILE      SQLITE_FCNTL_SET_LOCKPROXYFILE
#define SQLITE_LAST_ERRNO             SQLITE_FCNTL_LAST_ERRNO

  }
  sqlite3_file_control(db, zDbName, SQLITE_FCNTL_TEMPFILENAME, (void*)&zTName);
  Tcl_AppendResult(interp, zTName, (char*)0);
  sqlite3_free(zTName);
  return TCL_OK;  
}

/*
** tclcmd:   file_control_external_reader DB ?AUXDB?
**
** Return a string that is a temporary filename
*/
static int SQLITE_TCLAPI file_control_external_reader(
  ClientData clientData, /* Pointer to sqlite3_enable_XXX function */
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int objc,              /* Number of arguments */
  Tcl_Obj *CONST objv[]  /* Command arguments */
){
  sqlite3 *db;
  const char *zName = "main";
  int iRes = 0;
  int rc = SQLITE_OK;

  if( objc!=2 && objc!=3 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"",
        Tcl_GetStringFromObj(objv[0], 0), " DB ?AUXDB?", 0);
    return TCL_ERROR;
  }
  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ){
    return TCL_ERROR;
  }
  if( objc==3 ){
    zName = Tcl_GetString(objv[2]);
  }
  rc = sqlite3_file_control(db, zName, SQLITE_FCNTL_EXTERNAL_READER, &iRes);
  if( rc!=SQLITE_OK ){
    Tcl_SetResult(interp, (char *)t1ErrorName(rc), TCL_STATIC);
    return TCL_ERROR;
  }
  Tcl_SetObjResult(interp, Tcl_NewIntObj(iRes));
  return TCL_OK;
}


/*
** tclcmd:   sqlite3_vfs_list
**
**   Return a tcl list containing the names of all registered vfs's.
*/
static int SQLITE_TCLAPI vfs_list(

     { "file_control_win32_set_handle", file_control_win32_set_handle, 0  },
#endif
     { "file_control_persist_wal",    file_control_persist_wal,     0   },
     { "file_control_powersafe_overwrite",file_control_powersafe_overwrite,0},
     { "file_control_vfsname",        file_control_vfsname,         0   },
     { "file_control_reservebytes",   file_control_reservebytes,    0   },
     { "file_control_tempfilename",   file_control_tempfilename,    0   },
     { "file_control_external_reader",   file_control_external_reader,    0   },
     { "sqlite3_vfs_list",           vfs_list,     0   },
     { "sqlite3_create_function_v2", test_create_function_v2, 0 },

     /* Functions from os.h */
#ifndef SQLITE_OMIT_UTF16
     { "add_test_collate",        test_collate, 0            },
     { "add_test_collate_needed", test_collate_needed, 0     },

# 2021 April 2
#
# 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.
#
#***********************************************************************
#

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

ifcapable !wal {
  finish_test 
  return 
}
if {$::tcl_platform(platform)!="unix"} {
  finish_test 
  return
}

do_multiclient_test tn {

  set bExternal 1
  if {[info commands db3]!=""} { set bExternal 0 }

  do_test 1.$tn.0 {
    sql1 {
      PRAGMA journal_mode = wal;
      CREATE TABLE t1(a, b);
      INSERT INTO t1 VALUES(1, 2);
    }
  } {wal}

  do_test 1.$tn.1 {
    sql2 { SELECT * FROM t1 }
  } {1 2}

  do_test 1.$tn.2 {
    code1 {
      file_control_external_reader db
    } 
  } {0}

  do_test 1.$tn.3 {
    sql2 { 
      BEGIN;
        SELECT * FROM t1;
    }
  } {1 2}

  do_test 1.$tn.4 {
    code1 {
      file_control_external_reader db
    } 
  } $bExternal

  do_test 1.$tn.5 {
    sql2 { COMMIT }
  } {}

  do_test 1.$tn.6 {
    code1 { file_control_external_reader db } 
  } 0

}


finish_test