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Overview
Comment:Avoid a race condition in the sqlite3_release_memory() logic within pager.c.
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Timelines: family | ancestors | descendants | both | branch-3.5.9
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SHA1: a718e6634795a48b5dd5c08833ab561e6381a62d
User & Date: drh 2010-01-30 19:17:07.000
Context
2010-01-30
22:28
Always hold the MEM2 mutex when initially marking a pager as in use by its database connection. (check-in: 622c17177a user: drh tags: branch-3.5.9)
19:17
Avoid a race condition in the sqlite3_release_memory() logic within pager.c. (check-in: a718e66347 user: drh tags: branch-3.5.9)
19:00
Remove all cache pages from the LRU list prior to removing the pager from the pager list when closing a pager. (check-in: 9d13acc449 user: drh tags: branch-3.5.9)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/pager.c.
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  */
  for(pPager=sqlite3PagerList; pPager; pPager=pPager->pNext){
     pPager->iInUseMM = 1;
  }

  while( rc==SQLITE_OK && (nReq<0 || nReleased<nReq) ){
    PgHdr *pPg;
    PgHdr *pRecycled;
 
    /* Try to find a page to recycle that does not require a sync(). If
    ** this is not possible, find one that does require a sync().
    */
    sqlite3_mutex_enter(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU));
    pPg = sqlite3LruPageList.pFirstSynced;
    while( pPg && (pPg->needSync || pPg->pPager->iInUseDB) ){








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  */
  for(pPager=sqlite3PagerList; pPager; pPager=pPager->pNext){
     pPager->iInUseMM = 1;
  }

  while( rc==SQLITE_OK && (nReq<0 || nReleased<nReq) ){
    PgHdr *pPg;

 
    /* Try to find a page to recycle that does not require a sync(). If
    ** this is not possible, find one that does require a sync().
    */
    sqlite3_mutex_enter(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU));
    pPg = sqlite3LruPageList.pFirstSynced;
    while( pPg && (pPg->needSync || pPg->pPager->iInUseDB) ){
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    /* If pPg==0, then the block above has failed to find a page to
    ** recycle. In this case return early - no further memory will
    ** be released.
    */
    if( !pPg ) break;

    pPager = pPg->pPager;
    assert(!pPg->needSync || pPg==pPager->lru.pFirst);
    assert(pPg->needSync || pPg==pPager->lru.pFirstSynced);
  
    savedBusy = pPager->pBusyHandler;
    pPager->pBusyHandler = 0;
    rc = pager_recycle(pPager, &pRecycled);
    pPager->pBusyHandler = savedBusy;
    assert(pRecycled==pPg || rc!=SQLITE_OK);
    if( rc==SQLITE_OK ){
      /* We've found a page to free. At this point the page has been 
      ** removed from the page hash-table, free-list and synced-list 
      ** (pFirstSynced). It is still in the all pages (pAll) list. 
      ** Remove it from this list before freeing.
      **
      ** Todo: Check the Pager.pStmt list to make sure this is Ok. It 








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    /* If pPg==0, then the block above has failed to find a page to
    ** recycle. In this case return early - no further memory will
    ** be released.
    */
    if( !pPg ) break;

    pPager = pPg->pPager;



    savedBusy = pPager->pBusyHandler;
    pPager->pBusyHandler = 0;
    rc = pager_recycle(pPager, &pPg);
    pPager->pBusyHandler = savedBusy;

    if( rc==SQLITE_OK ){
      /* We've found a page to free. At this point the page has been 
      ** removed from the page hash-table, free-list and synced-list 
      ** (pFirstSynced). It is still in the all pages (pAll) list. 
      ** Remove it from this list before freeing.
      **
      ** Todo: Check the Pager.pStmt list to make sure this is Ok. It
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