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Simplifications to the SHM locking implementation in os_unix.c.

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FossilOrigin-Name: 9de05bfb09e29bafdf5782263330fe8eefcfaba3
This commit is contained in:
drh
2010-05-05 18:20:07 +00:00
parent 3289c5efc8
commit 4bc79def36
3 changed files with 26 additions and 34 deletions
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40
src/os_unix.c
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@@ -4648,7 +4648,6 @@ struct unixShm {
unixShmFile *pFile; /* The underlying unixShmFile object */
unixShm *pNext; /* Next unixShm with the same unixShmFile */
u8 lockState; /* Current lock state */
u8 readLock; /* Which of the two read-lock states to use */
u8 hasMutex; /* True if holding the unixShmFile mutex */
u8 hasMutexBuf; /* True if holding pFile->mutexBuf */
u8 sharedMask; /* Mask of shared locks held */
@@ -4667,8 +4666,7 @@ struct unixShm {
** Constants used for locking
*/
#define UNIX_SHM_BASE 32 /* Byte offset of the first lock byte */
#define UNIX_SHM_MUTEX 0x01 /* Mask for MUTEX lock */
#define UNIX_SHM_DMS 0x04 /* Mask for Dead-Man-Switch lock */
#define UNIX_SHM_DMS 0x01 /* Mask for Dead-Man-Switch lock */
#define UNIX_SHM_A 0x10 /* Mask for region locks... */
#define UNIX_SHM_B 0x20
#define UNIX_SHM_C 0x40
@@ -4695,13 +4693,12 @@ static const char *unixShmLockString(u8 mask){
iBuf += 8;
if( iBuf>=sizeof(zBuf) ) iBuf = 0;
z[0] = (mask & UNIX_SHM_MUTEX) ? 'M' : '.';
z[1] = (mask & UNIX_SHM_DMS) ? 'S' : '.';
z[2] = (mask & UNIX_SHM_A) ? 'A' : '.';
z[3] = (mask & UNIX_SHM_B) ? 'B' : '.';
z[4] = (mask & UNIX_SHM_C) ? 'C' : '.';
z[5] = (mask & UNIX_SHM_D) ? 'D' : '.';
z[6] = 0;
z[0] = (mask & UNIX_SHM_DMS) ? 'S' : '.';
z[1] = (mask & UNIX_SHM_A) ? 'A' : '.';
z[2] = (mask & UNIX_SHM_B) ? 'B' : '.';
z[3] = (mask & UNIX_SHM_C) ? 'C' : '.';
z[4] = (mask & UNIX_SHM_D) ? 'D' : '.';
z[5] = 0;
return z;
}
#endif /* SQLITE_DEBUG */
@@ -4712,7 +4709,7 @@ static const char *unixShmLockString(u8 mask){
** lockMask might contain multiple bits but all bits are guaranteed
** to be contiguous.
**
** Locks block if the UNIX_SHM_MUTEX bit is set and are non-blocking
** Locks block if the mask is exactly UNIX_SHM_C and are non-blocking
** otherwise.
*/
static int unixShmSystemLock(
@@ -4733,7 +4730,7 @@ static int unixShmSystemLock(
memset(&f, 0, sizeof(f));
f.l_type = lockType;
f.l_whence = SEEK_SET;
if( (lockMask & UNIX_SHM_MUTEX)!=0 && lockType!=F_UNLCK ){
if( lockMask==UNIX_SHM_C && lockType!=F_UNLCK ){
lockOp = F_SETLKW;
OSTRACE(("SHM-LOCK requesting blocking lock\n"));
}else{
@@ -5029,10 +5026,6 @@ static int unixShmOpen(
/* Check to see if another process is holding the dead-man switch.
** If not, truncate the file to zero length.
*/
if( unixShmSystemLock(pFile, F_WRLCK, UNIX_SHM_MUTEX) ){
rc = SQLITE_IOERR_LOCK;
goto shm_open_err;
}
if( unixShmSystemLock(pFile, F_WRLCK, UNIX_SHM_DMS)==SQLITE_OK ){
if( ftruncate(pFile->h, 0) ){
rc = SQLITE_IOERR;
@@ -5041,7 +5034,6 @@ static int unixShmOpen(
if( rc==SQLITE_OK ){
rc = unixShmSystemLock(pFile, F_RDLCK, UNIX_SHM_DMS);
}
unixShmSystemLock(pFile, F_UNLCK, UNIX_SHM_MUTEX);
if( rc ) goto shm_open_err;
}
@@ -5321,21 +5313,21 @@ static int unixShmLock(
if( rc==SQLITE_BUSY ){
rc = unixShmSharedLock(pFile, p, UNIX_SHM_D);
if( rc==SQLITE_OK ){
p->lockState = p->readLock = SQLITE_SHM_READ_FULL;
p->lockState = SQLITE_SHM_READ_FULL;
}
}else{
unixShmUnlock(pFile, p, UNIX_SHM_B);
p->lockState = p->readLock = SQLITE_SHM_READ;
p->lockState = SQLITE_SHM_READ;
}
}
}else if( p->lockState==SQLITE_SHM_WRITE ){
rc = unixShmSharedLock(pFile, p, UNIX_SHM_A);
unixShmUnlock(pFile, p, UNIX_SHM_C|UNIX_SHM_D);
p->lockState = p->readLock = SQLITE_SHM_READ;
p->lockState = SQLITE_SHM_READ;
}else{
assert( p->lockState==SQLITE_SHM_RECOVER );
unixShmUnlock(pFile, p, UNIX_SHM_MUTEX);
p->lockState = p->readLock;
unixShmUnlock(pFile, p, UNIX_SHM_C);
p->lockState = SQLITE_SHM_READ;
rc = SQLITE_OK;
}
break;
@@ -5354,7 +5346,7 @@ static int unixShmLock(
|| p->lockState==SQLITE_SHM_PENDING
|| p->lockState==SQLITE_SHM_RECOVER );
if( p->lockState==SQLITE_SHM_RECOVER ){
unixShmUnlock(pFile, p, UNIX_SHM_MUTEX);
unixShmUnlock(pFile, p, UNIX_SHM_C);
p->lockState = SQLITE_SHM_CHECKPOINT;
rc = SQLITE_OK;
}
@@ -5378,7 +5370,7 @@ static int unixShmLock(
|| p->lockState==SQLITE_SHM_READ_FULL
|| p->lockState==SQLITE_SHM_CHECKPOINT );
assert( sqlite3_mutex_held(pFile->mutexBuf) );
rc = unixShmExclusiveLock(pFile, p, UNIX_SHM_MUTEX);
rc = unixShmExclusiveLock(pFile, p, UNIX_SHM_C);
if( rc==SQLITE_OK ){
p->lockState = SQLITE_SHM_RECOVER;
}