database/sqlite
1
0
Fork 0
mirror of https://github.com/sqlite/sqlite.git synced 2025-11-12 13:01:09 +03:00
Code Activity

Define an invariant to guarantee deadlock-free operation of SHM in os_unix.c

Browse Source 
and check that invariant with assert() statements.

FossilOrigin-Name: 6af2dca75b8139134ea394c1d71aefc6523f02e9
This commit is contained in:
drh
2010-05-01 17:57:36 +00:00
parent 77b95a379c
commit bee6f4ebe2
3 changed files with 19 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
src/os_unix.c
View File

@@ -4589,6 +4589,12 @@ typedef struct unixShmFile unixShmFile;
** 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 */
@@ -5146,6 +5152,7 @@ static int unixShmGet(
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;
}
@@ -5184,6 +5191,7 @@ 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;
}
@@ -5246,6 +5254,7 @@ static int unixShmLock(
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;
}