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Modify the unixShmLock() function to avoid iterating through the (possibly large) set of connections to the same database file.

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FossilOrigin-Name: e0faddf0dfc3a40b6b94408296dd781dd0264ecc9f2129ce4405438433fb00e0
This commit is contained in:
dan
2020-08-28 19:27:15 +00:00
parent 832aa023c6
commit 8337da6678
3 changed files with 80 additions and 48 deletions
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111
src/os_unix.c
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@@ -4255,6 +4255,7 @@ struct unixShmNode {
char **apRegion; /* Array of mapped shared-memory regions */
int nRef; /* Number of unixShm objects pointing to this */
unixShm *pFirst; /* All unixShm objects pointing to this */
int aLock[SQLITE_SHM_NLOCK]; /* # shared locks on slot, -1==excl lock */
#ifdef SQLITE_DEBUG
u8 exclMask; /* Mask of exclusive locks held */
u8 sharedMask; /* Mask of shared locks held */
@@ -4795,6 +4796,38 @@ shmpage_out:
return rc;
}
/*
** Check that the pShmNode->aLock[] array comports with the locking bitmasks
** held by each client. Return true if it does, or false otherwise. This
** is to be used in an assert(). e.g.
**
** assert( assertLockingArrayOk(pShmNode) );
*/
#ifdef SQLITE_DEBUG
static int assertLockingArrayOk(unixShmNode *pShmNode){
unixShm *pX;
int aLock[SQLITE_SHM_NLOCK];
assert( sqlite3_mutex_held(pShmNode->pShmMutex) );
memset(aLock, 0, sizeof(aLock));
for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
int i;
for(i=0; i<SQLITE_SHM_NLOCK; i++){
if( pX->exclMask & (1<<i) ){
assert( aLock[i]==0 );
aLock[i] = -1;
}else if( pX->sharedMask & (1<<i) ){
assert( aLock[i]>=0 );
aLock[i]++;
}
}
}
assert( 0==memcmp(pShmNode->aLock, aLock, sizeof(aLock)) );
return (memcmp(pShmNode->aLock, aLock, sizeof(aLock))==0);
}
#endif
/*
** Change the lock state for a shared-memory segment.
**
@@ -4811,10 +4844,10 @@ static int unixShmLock(
){
unixFile *pDbFd = (unixFile*)fd; /* Connection holding shared memory */
unixShm *p = pDbFd->pShm; /* The shared memory being locked */
unixShm *pX; /* For looping over all siblings */
unixShmNode *pShmNode = p->pShmNode; /* The underlying file iNode */
int rc = SQLITE_OK; /* Result code */
u16 mask; /* Mask of locks to take or release */
int *aLock = pShmNode->aLock;
assert( pShmNode==pDbFd->pInode->pShmNode );
assert( pShmNode->pInode==pDbFd->pInode );
@@ -4853,21 +4886,25 @@ static int unixShmLock(
mask = (1<<(ofst+n)) - (1<<ofst);
assert( n>1 || mask==(1<<ofst) );
sqlite3_mutex_enter(pShmNode->pShmMutex);
assert( assertLockingArrayOk(pShmNode) );
if( flags & SQLITE_SHM_UNLOCK ){
u16 allMask = 0; /* Mask of locks held by siblings */
int ii;
int bUnlock = 1;
/* See if any siblings hold this same lock */
for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
if( pX==p ) continue;
assert( (pX->exclMask & (p->exclMask|p->sharedMask))==0 );
allMask |= pX->sharedMask;
for(ii=ofst; ii<ofst+n; ii++){
if( aLock[ii]>((p->sharedMask & (1<<ii)) ? 1 : 0) ){
bUnlock = 0;
}
}
/* Unlock the system-level locks */
if( (mask & allMask)==0 ){
if( bUnlock ){
rc = unixShmSystemLock(pDbFd, F_UNLCK, ofst+UNIX_SHM_BASE, n);
}else{
rc = SQLITE_OK;
if( rc==SQLITE_OK ){
memset(&aLock[ofst], 0, sizeof(int)*n);
}
}else if( p->sharedMask & (1<<ofst) ){
assert( n==1 && aLock[ofst]>1 );
aLock[ofst]--;
}
/* Undo the local locks */
@@ -4876,55 +4913,47 @@ static int unixShmLock(
p->sharedMask &= ~mask;
}
}else if( flags & SQLITE_SHM_SHARED ){
u16 allShared = 0; /* Union of locks held by connections other than "p" */
/* Find out which shared locks are already held by sibling connections.
** If any sibling already holds an exclusive lock, go ahead and return
** SQLITE_BUSY.
*/
for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
if( (pX->exclMask & mask)!=0 ){
assert( n==1 );
assert( (p->exclMask & (1<<ofst))==0 );
if( (p->sharedMask & mask)==0 ){
if( aLock[ofst]<0 ){
rc = SQLITE_BUSY;
break;
}
allShared |= pX->sharedMask;
}
/* Get shared locks at the system level, if necessary */
if( rc==SQLITE_OK ){
if( (allShared & mask)==0 ){
}else if( aLock[ofst]==0 ){
rc = unixShmSystemLock(pDbFd, F_RDLCK, ofst+UNIX_SHM_BASE, n);
}else{
rc = SQLITE_OK;
}
}
/* Get the local shared locks */
if( rc==SQLITE_OK ){
p->sharedMask |= mask;
/* Get the local shared locks */
if( rc==SQLITE_OK ){
p->sharedMask |= mask;
aLock[ofst]++;
}
}
}else{
/* Make sure no sibling connections hold locks that will block this
** lock. If any do, return SQLITE_BUSY right away.
*/
for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
if( (pX->exclMask & mask)!=0 || (pX->sharedMask & mask)!=0 ){
** lock. If any do, return SQLITE_BUSY right away. */
int ii;
for(ii=ofst; ii<ofst+n; ii++){
assert( (p->sharedMask & mask)==0 );
if( (p->exclMask & (1<<ii))==0 && aLock[ii] ){
rc = SQLITE_BUSY;
break;
}
}
/* Get the exclusive locks at the system level. Then if successful
** also mark the local connection as being locked.
*/
/* Get the exclusive locks at the system level. Then if successful
** also update the in-memory values. */
if( rc==SQLITE_OK ){
rc = unixShmSystemLock(pDbFd, F_WRLCK, ofst+UNIX_SHM_BASE, n);
if( rc==SQLITE_OK ){
assert( (p->sharedMask & mask)==0 );
p->exclMask |= mask;
for(ii=ofst; ii<ofst+n; ii++){
aLock[ii] = -1;
}
}
}
}
assert( assertLockingArrayOk(pShmNode) );
sqlite3_mutex_leave(pShmNode->pShmMutex);
OSTRACE(("SHM-LOCK shmid-%d, pid-%d got %03x,%03x\n",
p->id, osGetpid(0), p->sharedMask, p->exclMask));