1 files changed, 35 insertions, 24 deletions

diff --git a/src/pcache1.c b/src/pcache1.c
index 4147d2e..1644b06 100644
--- a/src/pcache1.c
+++ b/src/pcache1.c
@@ -96,6 +96,7 @@ struct PCache1 {
 struct PgHdr1 {
   sqlite3_pcache_page page;
   unsigned int iKey;             /* Key value (page number) */
+  u8 isPinned;                   /* Page in use, not on the LRU list */
   PgHdr1 *pNext;                 /* Next in hash table chain */
   PCache1 *pCache;               /* Cache that currently owns this page */
   PgHdr1 *pLruNext;              /* Next in LRU list of unpinned pages */
@@ -424,34 +425,32 @@ static int pcache1ResizeHash(PCache1 *p){
 ** LRU list, then this function is a no-op.
 **
 ** The PGroup mutex must be held when this function is called.
-**
-** If pPage is NULL then this routine is a no-op.
 */
 static void pcache1PinPage(PgHdr1 *pPage){
   PCache1 *pCache;
   PGroup *pGroup;
 
-  if( pPage==0 ) return;
+  assert( pPage!=0 );
+  assert( pPage->isPinned==0 );
   pCache = pPage->pCache;
   pGroup = pCache->pGroup;
+  assert( pPage->pLruNext || pPage==pGroup->pLruTail );
+  assert( pPage->pLruPrev || pPage==pGroup->pLruHead );
   assert( sqlite3_mutex_held(pGroup->mutex) );
-  if( pPage->pLruNext || pPage==pGroup->pLruTail ){
-    if( pPage->pLruPrev ){
-      pPage->pLruPrev->pLruNext = pPage->pLruNext;
-    }
-    if( pPage->pLruNext ){
-      pPage->pLruNext->pLruPrev = pPage->pLruPrev;
-    }
-    if( pGroup->pLruHead==pPage ){
-      pGroup->pLruHead = pPage->pLruNext;
-    }
-    if( pGroup->pLruTail==pPage ){
-      pGroup->pLruTail = pPage->pLruPrev;
-    }
-    pPage->pLruNext = 0;
-    pPage->pLruPrev = 0;
-    pPage->pCache->nRecyclable--;
+  if( pPage->pLruPrev ){
+    pPage->pLruPrev->pLruNext = pPage->pLruNext;
+  }else{
+    pGroup->pLruHead = pPage->pLruNext;
+  }
+  if( pPage->pLruNext ){
+    pPage->pLruNext->pLruPrev = pPage->pLruPrev;
+  }else{
+    pGroup->pLruTail = pPage->pLruPrev;
   }
+  pPage->pLruNext = 0;
+  pPage->pLruPrev = 0;
+  pPage->isPinned = 1;
+  pCache->nRecyclable--;
 }
 
 
@@ -483,6 +482,7 @@ static void pcache1EnforceMaxPage(PGroup *pGroup){
   while( pGroup->nCurrentPage>pGroup->nMaxPage && pGroup->pLruTail ){
     PgHdr1 *p = pGroup->pLruTail;
     assert( p->pCache->pGroup==pGroup );
+    assert( p->isPinned==0 );
     pcache1PinPage(p);
     pcache1RemoveFromHash(p);
     pcache1FreePage(p);
@@ -510,7 +510,7 @@ static void pcache1TruncateUnsafe(
       if( pPage->iKey>=iLimit ){
         pCache->nPage--;
         *pp = pPage->pNext;
-        pcache1PinPage(pPage);
+        if( !pPage->isPinned ) pcache1PinPage(pPage);
         pcache1FreePage(pPage);
       }else{
         pp = &pPage->pNext;
@@ -562,7 +562,7 @@ static sqlite3_pcache *pcache1Create(int szPage, int szExtra, int bPurgeable){
   int sz;               /* Bytes of memory required to allocate the new cache */
 
   /*
-  ** The seperateCache variable is true if each PCache has its own private
+  ** The separateCache variable is true if each PCache has its own private
   ** PGroup.  In other words, separateCache is true for mode (1) where no
   ** mutexing is required.
   **
@@ -720,6 +720,7 @@ static sqlite3_pcache_page *pcache1Fetch(
   PGroup *pGroup;
   PgHdr1 *pPage = 0;
 
+  assert( offsetof(PgHdr1,page)==0 );
   assert( pCache->bPurgeable || createFlag!=1 );
   assert( pCache->bPurgeable || pCache->nMin==0 );
   assert( pCache->bPurgeable==0 || pCache->nMin==10 );
@@ -733,8 +734,11 @@ static sqlite3_pcache_page *pcache1Fetch(
   }
 
   /* Step 2: Abort if no existing page is found and createFlag is 0 */
-  if( pPage || createFlag==0 ){
-    pcache1PinPage(pPage);
+  if( pPage ){
+    if( !pPage->isPinned ) pcache1PinPage(pPage);
+    goto fetch_out;
+  }
+  if( createFlag==0 ){
     goto fetch_out;
   }
 
@@ -765,6 +769,7 @@ static sqlite3_pcache_page *pcache1Fetch(
   if( pCache->nPage>=pCache->nHash && pcache1ResizeHash(pCache) ){
     goto fetch_out;
   }
+  assert( pCache->nHash>0 && pCache->apHash );
 
   /* Step 4. Try to recycle a page. */
   if( pCache->bPurgeable && pGroup->pLruTail && (
@@ -774,6 +779,7 @@ static sqlite3_pcache_page *pcache1Fetch(
   )){
     PCache1 *pOther;
     pPage = pGroup->pLruTail;
+    assert( pPage->isPinned==0 );
     pcache1RemoveFromHash(pPage);
     pcache1PinPage(pPage);
     pOther = pPage->pCache;
@@ -810,6 +816,7 @@ static sqlite3_pcache_page *pcache1Fetch(
     pPage->pCache = pCache;
     pPage->pLruPrev = 0;
     pPage->pLruNext = 0;
+    pPage->isPinned = 1;
     *(void **)pPage->page.pExtra = 0;
     pCache->apHash[h] = pPage;
   }
@@ -819,7 +826,7 @@ fetch_out:
     pCache->iMaxKey = iKey;
   }
   pcache1LeaveMutex(pGroup);
-  return &pPage->page;
+  return (sqlite3_pcache_page*)pPage;
 }
 
 
@@ -845,6 +852,7 @@ static void pcache1Unpin(
   */
   assert( pPage->pLruPrev==0 && pPage->pLruNext==0 );
   assert( pGroup->pLruHead!=pPage && pGroup->pLruTail!=pPage );
+  assert( pPage->isPinned==1 );
 
   if( reuseUnlikely || pGroup->nCurrentPage>pGroup->nMaxPage ){
     pcache1RemoveFromHash(pPage);
@@ -860,6 +868,7 @@ static void pcache1Unpin(
       pGroup->pLruHead = pPage;
     }
     pCache->nRecyclable++;
+    pPage->isPinned = 0;
   }
 
   pcache1LeaveMutex(pCache->pGroup);
@@ -986,6 +995,7 @@ int sqlite3PcacheReleaseMemory(int nReq){
 #ifdef SQLITE_PCACHE_SEPARATE_HEADER
       nFree += sqlite3MemSize(p);
 #endif
+      assert( p->isPinned==0 );
       pcache1PinPage(p);
       pcache1RemoveFromHash(p);
       pcache1FreePage(p);
@@ -1010,6 +1020,7 @@ void sqlite3PcacheStats(
   PgHdr1 *p;
   int nRecyclable = 0;
   for(p=pcache1.grp.pLruHead; p; p=p->pLruNext){
+    assert( p->isPinned==0 );
     nRecyclable++;
   }
   *pnCurrent = pcache1.grp.nCurrentPage;