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Fix a race condition that can lead to deadlock in the memdb VFS if one

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thread is trying to open an existing database at the same moment that
another thread that is the only prior user of that database is trying to
close it.

FossilOrigin-Name: b635375dbe22bd31c437ca574eb0c014c0b045de6cc0816c32d2ceceff9191fb
This commit is contained in:
drh
2021-05-12 15:39:02 +00:00
parent 85ffcae177
commit 52d1407891
3 changed files with 26 additions and 22 deletions
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32
src/memdb.c
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@@ -196,29 +196,33 @@ static void memdbLeave(MemStore *p){
*/
static int memdbClose(sqlite3_file *pFile){
MemStore *p = ((MemFile*)pFile)->pStore;
memdbEnter(p);
p->nRef--;
if( p->nRef<=0 ){
if( p->mFlags & SQLITE_DESERIALIZE_FREEONCLOSE ){
sqlite3_free(p->aData);
}
if( p->zFName ){
int i;
if( p->zFName ){
int i;
#ifndef SQLITE_MUTEX_OMIT
sqlite3_mutex *pVfsMutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1);
sqlite3_mutex *pVfsMutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1);
#endif
sqlite3_mutex_enter(pVfsMutex);
for(i=0; ALWAYS(i<memdb_g.nMemStore); i++){
if( memdb_g.apMemStore[i]==p ){
sqlite3_mutex_enter(pVfsMutex);
for(i=0; ALWAYS(i<memdb_g.nMemStore); i++){
if( memdb_g.apMemStore[i]==p ){
memdbEnter(p);
if( p->nRef==1 ){
memdb_g.apMemStore[i] = memdb_g.apMemStore[--memdb_g.nMemStore];
if( memdb_g.nMemStore==0 ){
sqlite3_free(memdb_g.apMemStore);
memdb_g.apMemStore = 0;
}
break;
}
break;
}
sqlite3_mutex_leave(pVfsMutex);
}
sqlite3_mutex_leave(pVfsMutex);
}else{
memdbEnter(p);
}
p->nRef--;
if( p->nRef<=0 ){
if( p->mFlags & SQLITE_DESERIALIZE_FREEONCLOSE ){
sqlite3_free(p->aData);
}
memdbLeave(p);
sqlite3_mutex_free(p->pMutex);