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Overview
| Comment: | Define an invariant to guarantee deadlock-free operation of SHM in os_unix.c and check that invariant with assert() statements. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | wal |
| Files: | files | file ages | folders |
| SHA1: |
6af2dca75b8139134ea394c1d71aefc6 |
| User & Date: | drh 2010-05-01 17:57:36 |
Context
|
2010-05-03
| ||
| 08:04 | Add the sqlite3_wal_checkpoint() and sqlite3_wal_autocheckpoint() APIs. check-in: 9803196d user: dan tags: wal | |
|
2010-05-01
| ||
| 18:23 | Remove the xShmPush and xShmPull methods from the VFS. check-in: 69e07fdb user: drh tags: wal | |
| 17:57 | Define an invariant to guarantee deadlock-free operation of SHM in os_unix.c and check that invariant with assert() statements. check-in: 6af2dca7 user: drh tags: wal | |
| 17:50 | Rework mutexes on the SHM implemention for os_unix to avoid a deadlock during WAL recovery. check-in: 1a0f69be user: drh tags: wal | |
Changes
Changes to src/os_unix.c.
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**
** fid
** zFilename
**
** Either unixShmFile.mutex must be held or unixShmFile.nRef==0 and
** unixMutexHeld() is true when reading or writing any other field
** in this structure.
*/
struct unixShmFile {
struct unixFileId fid; /* Unique file identifier */
sqlite3_mutex *mutex; /* Mutex to access this object */
sqlite3_mutex *mutexBuf; /* Mutex to access zBuf[] */
char *zFilename; /* Name of the file */
int h; /* Open file descriptor */
................................................................................
void **ppBuf /* Write mapping buffer origin here */
){
unixShm *p = (unixShm*)pSharedMem;
unixShmFile *pFile = p->pFile;
int rc = SQLITE_OK;
if( p->lockState!=SQLITE_SHM_CHECKPOINT && p->hasMutexBuf==0 ){
sqlite3_mutex_enter(pFile->mutexBuf);
p->hasMutexBuf = 1;
}
sqlite3_mutex_enter(pFile->mutex);
if( pFile->szMap==0 || reqMapSize>pFile->szMap ){
int actualSize;
if( unixShmSize(pSharedMem, -1, &actualSize)==SQLITE_OK
................................................................................
** really want to release the lock, so in that case too, this routine
** is a no-op.
*/
static int unixShmRelease(sqlite3_shm *pSharedMem){
unixShm *p = (unixShm*)pSharedMem;
if( p->hasMutexBuf && p->lockState!=SQLITE_SHM_RECOVER ){
unixShmFile *pFile = p->pFile;
sqlite3_mutex_leave(pFile->mutexBuf);
p->hasMutexBuf = 0;
}
return SQLITE_OK;
}
/*
................................................................................
return SQLITE_OK;
}
OSTRACE(("SHM-LOCK shmid-%d, pid-%d request %s->%s\n",
p->id, getpid(), azLkName[p->lockState], azLkName[desiredLock]));
if( desiredLock==SQLITE_SHM_RECOVER && !p->hasMutexBuf ){
sqlite3_mutex_enter(pFile->mutexBuf);
p->hasMutexBuf = 1;
}
sqlite3_mutex_enter(pFile->mutex);
switch( desiredLock ){
case SQLITE_SHM_UNLOCK: {
assert( p->lockState!=SQLITE_SHM_RECOVER );
|
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** ** fid ** zFilename ** ** Either unixShmFile.mutex must be held or unixShmFile.nRef==0 and ** unixMutexHeld() is true when reading or writing any other field ** in this structure. ** ** To avoid deadlocks, mutex and mutexBuf are always released in the ** reverse order that they are acquired. mutexBuf is always acquired ** first and released last. This invariant is check by asserting ** sqlite3_mutex_notheld() on mutex whenever mutexBuf is acquired or ** released. */ struct unixShmFile { struct unixFileId fid; /* Unique file identifier */ sqlite3_mutex *mutex; /* Mutex to access this object */ sqlite3_mutex *mutexBuf; /* Mutex to access zBuf[] */ char *zFilename; /* Name of the file */ int h; /* Open file descriptor */ ................................................................................ void **ppBuf /* Write mapping buffer origin here */ ){ unixShm *p = (unixShm*)pSharedMem; unixShmFile *pFile = p->pFile; int rc = SQLITE_OK; if( p->lockState!=SQLITE_SHM_CHECKPOINT && p->hasMutexBuf==0 ){ assert( sqlite3_mutex_notheld(pFile->mutex) ); sqlite3_mutex_enter(pFile->mutexBuf); p->hasMutexBuf = 1; } sqlite3_mutex_enter(pFile->mutex); if( pFile->szMap==0 || reqMapSize>pFile->szMap ){ int actualSize; if( unixShmSize(pSharedMem, -1, &actualSize)==SQLITE_OK ................................................................................ ** really want to release the lock, so in that case too, this routine ** is a no-op. */ static int unixShmRelease(sqlite3_shm *pSharedMem){ unixShm *p = (unixShm*)pSharedMem; if( p->hasMutexBuf && p->lockState!=SQLITE_SHM_RECOVER ){ unixShmFile *pFile = p->pFile; assert( sqlite3_mutex_notheld(pFile->mutex) ); sqlite3_mutex_leave(pFile->mutexBuf); p->hasMutexBuf = 0; } return SQLITE_OK; } /* ................................................................................ return SQLITE_OK; } OSTRACE(("SHM-LOCK shmid-%d, pid-%d request %s->%s\n", p->id, getpid(), azLkName[p->lockState], azLkName[desiredLock])); if( desiredLock==SQLITE_SHM_RECOVER && !p->hasMutexBuf ){ assert( sqlite3_mutex_notheld(pFile->mutex) ); sqlite3_mutex_enter(pFile->mutexBuf); p->hasMutexBuf = 1; } sqlite3_mutex_enter(pFile->mutex); switch( desiredLock ){ case SQLITE_SHM_UNLOCK: { assert( p->lockState!=SQLITE_SHM_RECOVER ); |