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Improve the logLockRegion() function in log.c.

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FossilOrigin-Name: 5e9dd3bd8e829376408925fb4cfcd5bb1eb1105f
This commit is contained in:
dan
2010-04-14 15:49:40 +00:00
parent b9bf16bfde
commit 02bb596649
3 changed files with 100 additions and 48 deletions
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src/log.c
+93 -41
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@@ -989,84 +989,129 @@ static void logLeaveMutex(Log *pLog){
static int logLockRegion(Log *pLog, u32 mRegion, int op){
LogSummary *pSummary = pLog->pSummary;
LogLock *p; /* Used to iterate through in-process locks */
u32 mNew; /* New locks on file */
u32 mOld; /* Old locks on file */
u32 mNewLock; /* New locks held by pLog */
u32 mOther; /* Locks held by other connections */
u32 mNew; /* New mask for pLog */
assert(
/* Writer lock operations */
(op==LOG_WRLOCK && mRegion==(LOG_REGION_C|LOG_REGION_D))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_C|LOG_REGION_D))
/* Reader lock operations */
/* Normal reader lock operations */
|| (op==LOG_RDLOCK && mRegion==(LOG_REGION_A|LOG_REGION_B))
|| (op==LOG_RDLOCK && mRegion==(LOG_REGION_D))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_A))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_B))
/* Region D reader lock operations */
|| (op==LOG_RDLOCK && mRegion==(LOG_REGION_D))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_D))
/* Checkpointer lock operations */
|| (op==LOG_WRLOCK && mRegion==(LOG_REGION_B|LOG_REGION_C))
|| (op==LOG_WRLOCK && mRegion==(LOG_REGION_A))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_A|LOG_REGION_B|LOG_REGION_C))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_B|LOG_REGION_C))
|| (op==LOG_UNLOCK && mRegion==(LOG_REGION_A|LOG_REGION_B|LOG_REGION_C))
);
/* Assert that a connection never tries to go from an EXCLUSIVE to a
** SHARED lock on a region. Moving from SHARED to EXCLUSIVE sometimes
** happens though (when a region D reader upgrades to a writer).
*/
assert( op!=LOG_RDLOCK || 0==(pLog->lock.mLock & (mRegion<<8)) );
sqlite3_mutex_enter(pSummary->mutex);
/* If obtaining (not releasing) a lock, check if there exist any
** conflicting locks in process. Return SQLITE_BUSY in this case.
/* Calculate a mask of logs held by all connections in this process apart
** from this one. The least significant byte of the mask contains a mask
** of the SHARED logs held. The next least significant byte of the mask
** indicates the EXCLUSIVE locks held. For example, to test if some other
** connection is holding a SHARED lock on region A, or an EXCLUSIVE lock
** on region C, do:
**
** hasSharedOnA = (mOther & (LOG_REGION_A<<0));
** hasExclusiveOnC = (mOther & (LOG_REGION_C<<8));
**
** In all masks, if the bit in the EXCLUSIVE byte mask is set, so is the
** corresponding bit in the SHARED mask.
*/
if( op ){
u32 mConflict = (mRegion<<8) | ((op==LOG_WRLOCK) ? mRegion : 0);
for(p=pSummary->pLock; p; p=p->pNext){
if( p!=&pLog->lock && (p->mLock & mConflict) ){
sqlite3_mutex_leave(pSummary->mutex);
return SQLITE_BUSY;
}
mOther = 0;
for(p=pSummary->pLock; p; p=p->pNext){
assert( (p->mLock & (p->mLock<<8))==(p->mLock&0x0000FF00) );
if( p!=&pLog->lock ){
mOther |= p->mLock;
}
}
/* Determine the new lock mask for this log connection */
/* If this call is to lock a region (not to unlock one), test if locks held
** by any other connection in this process prevent the new locks from
** begin granted. If so, exit the summary mutex and return SQLITE_BUSY.
*/
if( op && (mOther & (mRegion << (op==LOG_RDLOCK ? 8 : 0))) ){
sqlite3_mutex_leave(pSummary->mutex);
return SQLITE_BUSY;
}
/* Figure out the new log mask for this connection. */
switch( op ){
case LOG_UNLOCK:
mNewLock = (pLog->lock.mLock & ~(mRegion|(mRegion<<8)));
mNew = (pLog->lock.mLock & ~(mRegion|(mRegion<<8)));
break;
case LOG_RDLOCK:
mNewLock = ((pLog->lock.mLock & ~(mRegion<<8)) | mRegion);
mNew = (pLog->lock.mLock | mRegion);
break;
default:
assert( op==LOG_WRLOCK );
mNewLock = (pLog->lock.mLock | (mRegion<<8) | mRegion);
mNew = (pLog->lock.mLock | (mRegion<<8) | mRegion);
break;
}
/* Determine the current and desired sets of locks at the file level. */
mNew = 0;
for(p=pSummary->pLock; p; p=p->pNext){
assert( (p->mLock & (p->mLock<<8))==(p->mLock & 0x00000F00) );
if( p!=&pLog->lock ) mNew |= p->mLock;
/* Now modify the locks held on the log-summary file descriptor. This
** file descriptor is shared by all log connections in this process.
** Therefore:
**
** + If one or more log connections in this process hold a SHARED lock
** on a region, the file-descriptor should hold a SHARED lock on
** the file region.
**
** + If a log connection in this process holds an EXCLUSIVE lock on a
** region, the file-descriptor should also hold an EXCLUSIVE lock on
** the region in question.
**
** If this is an LOG_UNLOCK operation, only regions for which no other
** connection holds a lock should actually be unlocked. And if this
** is a LOG_RDLOCK operation and other connections already hold all
** the required SHARED locks, then no system call is required.
*/
if( op==LOG_UNLOCK ){
mRegion = (mRegion & ~mOther);
}
mOld = mNew | pLog->lock.mLock;
mNew = mNew | mNewLock;
if( (op==LOG_WRLOCK)
|| (op==LOG_UNLOCK && mRegion)
|| (op==LOG_RDLOCK && (mOther&mRegion)!=mRegion)
){
struct LockMap {
int iStart; /* Byte offset to start locking operation */
int iLen; /* Length field for locking operation */
} aMap[] = {
/* 0000 */ {0, 0}, /* 0001 */ {4, 1},
/* 0010 */ {3, 1}, /* 0011 */ {3, 2},
/* 0100 */ {2, 1}, /* 0101 */ {0, 0},
/* 0110 */ {2, 2}, /* 0111 */ {2, 3},
/* 1000 */ {1, 1}, /* 1001 */ {0, 0},
/* 1010 */ {0, 0}, /* 1011 */ {0, 0},
/* 1100 */ {1, 2}, /* 1101 */ {0, 0},
/* 1110 */ {1, 3}, /* 1111 */ {0, 0}
};
int rc; /* Return code of fcntl() */
struct flock f; /* Locking operation */
assert( mRegion<ArraySize(aMap) && aMap[mRegion].iStart!=0 );
if( mNew!=mOld ){
int rc;
u32 mChange = (mNew^mOld) | ((mNew^mOld)>>8);
struct flock f;
memset(&f, 0, sizeof(f));
f.l_type = (op==LOG_WRLOCK?F_WRLCK:(op==LOG_RDLOCK?F_RDLCK:F_UNLCK));
f.l_whence = SEEK_SET;
if( mChange & LOG_REGION_A ) f.l_start = 12;
else if( mChange & LOG_REGION_B ) f.l_start = 13;
else if( mChange & LOG_REGION_C ) f.l_start = 14;
else if( mChange & LOG_REGION_D ) f.l_start = 15;
if( mChange & LOG_REGION_D ) f.l_len = 16 - f.l_start;
else if( mChange & LOG_REGION_C ) f.l_len = 15 - f.l_start;
else if( mChange & LOG_REGION_B ) f.l_len = 14 - f.l_start;
else if( mChange & LOG_REGION_A ) f.l_len = 13 - f.l_start;
f.l_start = 32 + aMap[mRegion].iStart;
f.l_len = aMap[mRegion].iLen;
rc = fcntl(pSummary->fd, F_SETLK, &f);
if( rc!=0 ){
@@ -1075,7 +1120,7 @@ static int logLockRegion(Log *pLog, u32 mRegion, int op){
}
}
pLog->lock.mLock = mNewLock;
pLog->lock.mLock = mNew;
sqlite3_mutex_leave(pSummary->mutex);
return SQLITE_OK;
}
@@ -1306,6 +1351,13 @@ int sqlite3LogWriteLock(Log *pLog, int op){
return rc;
}
/* TODO: What if this is a region D reader? And after writing this
** transaction it continues to hold a read-lock on the db? Maybe we
** need to switch it to a region A reader here so that unlocking C|D
** does not leave the connection with no lock at all.
*/
assert( pLog->isLocked!=LOG_REGION_D );
if( memcmp(&pLog->hdr, pLog->pSummary->aData, sizeof(pLog->hdr)) ){
return SQLITE_BUSY;
}