diff options
Diffstat (limited to 'chromium/third_party/sqlite/src/src/pcache1.c')
| -rw-r--r-- | chromium/third_party/sqlite/src/src/pcache1.c | 73 |
1 files changed, 33 insertions, 40 deletions
diff --git a/chromium/third_party/sqlite/src/src/pcache1.c b/chromium/third_party/sqlite/src/src/pcache1.c index ce595f2c201..adbe953959b 100644 --- a/chromium/third_party/sqlite/src/src/pcache1.c +++ b/chromium/third_party/sqlite/src/src/pcache1.c @@ -39,12 +39,13 @@ ** size can vary according to architecture, compile-time options, and ** SQLite library version number. ** -** If SQLITE_PCACHE_SEPARATE_HEADER is defined, then the extension is obtained -** using a separate memory allocation from the database page content. This -** seeks to overcome the "clownshoe" problem (also called "internal -** fragmentation" in academic literature) of allocating a few bytes more -** than a power of two with the memory allocator rounding up to the next -** power of two, and leaving the rounded-up space unused. +** Historical note: It used to be that if the SQLITE_PCACHE_SEPARATE_HEADER +** was defined, then the page content would be held in a separate memory +** allocation from the PgHdr1. This was intended to avoid clownshoe memory +** allocations. However, the btree layer needs a small (16-byte) overrun +** area after the page content buffer. The header serves as that overrun +** area. Therefore SQLITE_PCACHE_SEPARATE_HEADER was discontinued to avoid +** any possibility of a memory error. ** ** This module tracks pointers to PgHdr1 objects. Only pcache.c communicates ** with this module. Information is passed back and forth as PgHdr1 pointers. @@ -89,30 +90,40 @@ typedef struct PGroup PGroup; /* ** Each cache entry is represented by an instance of the following -** structure. Unless SQLITE_PCACHE_SEPARATE_HEADER is defined, a buffer of -** PgHdr1.pCache->szPage bytes is allocated directly before this structure -** in memory. +** structure. A buffer of PgHdr1.pCache->szPage bytes is allocated +** directly before this structure and is used to cache the page content. ** -** Note: Variables isBulkLocal and isAnchor were once type "u8". That works, +** When reading a corrupt database file, it is possible that SQLite might +** read a few bytes (no more than 16 bytes) past the end of the page buffer. +** It will only read past the end of the page buffer, never write. This +** object is positioned immediately after the page buffer to serve as an +** overrun area, so that overreads are harmless. +** +** Variables isBulkLocal and isAnchor were once type "u8". That works, ** but causes a 2-byte gap in the structure for most architectures (since ** pointers must be either 4 or 8-byte aligned). As this structure is located ** in memory directly after the associated page data, if the database is ** corrupt, code at the b-tree layer may overread the page buffer and ** read part of this structure before the corruption is detected. This ** can cause a valgrind error if the unitialized gap is accessed. Using u16 -** ensures there is no such gap, and therefore no bytes of unitialized memory -** in the structure. +** ensures there is no such gap, and therefore no bytes of uninitialized +** memory in the structure. +** +** The pLruNext and pLruPrev pointers form a double-linked circular list +** of all pages that are unpinned. The PGroup.lru element (which should be +** the only element on the list with PgHdr1.isAnchor set to 1) forms the +** beginning and the end of the list. */ struct PgHdr1 { - sqlite3_pcache_page page; /* Base class. Must be first. pBuf & pExtra */ - unsigned int iKey; /* Key value (page number) */ - u16 isBulkLocal; /* This page from bulk local storage */ - u16 isAnchor; /* This is the PGroup.lru element */ - PgHdr1 *pNext; /* Next in hash table chain */ - PCache1 *pCache; /* Cache that currently owns this page */ - PgHdr1 *pLruNext; /* Next in LRU list of unpinned pages */ - PgHdr1 *pLruPrev; /* Previous in LRU list of unpinned pages */ - /* NB: pLruPrev is only valid if pLruNext!=0 */ + sqlite3_pcache_page page; /* Base class. Must be first. pBuf & pExtra */ + unsigned int iKey; /* Key value (page number) */ + u16 isBulkLocal; /* This page from bulk local storage */ + u16 isAnchor; /* This is the PGroup.lru element */ + PgHdr1 *pNext; /* Next in hash table chain */ + PCache1 *pCache; /* Cache that currently owns this page */ + PgHdr1 *pLruNext; /* Next in circular LRU list of unpinned pages */ + PgHdr1 *pLruPrev; /* Previous in LRU list of unpinned pages */ + /* NB: pLruPrev is only valid if pLruNext!=0 */ }; /* @@ -438,25 +449,13 @@ static PgHdr1 *pcache1AllocPage(PCache1 *pCache, int benignMalloc){ pcache1LeaveMutex(pCache->pGroup); #endif if( benignMalloc ){ sqlite3BeginBenignMalloc(); } -#ifdef SQLITE_PCACHE_SEPARATE_HEADER - pPg = pcache1Alloc(pCache->szPage); - p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra); - if( !pPg || !p ){ - pcache1Free(pPg); - sqlite3_free(p); - pPg = 0; - } -#else pPg = pcache1Alloc(pCache->szAlloc); -#endif if( benignMalloc ){ sqlite3EndBenignMalloc(); } #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT pcache1EnterMutex(pCache->pGroup); #endif if( pPg==0 ) return 0; -#ifndef SQLITE_PCACHE_SEPARATE_HEADER p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage]; -#endif p->page.pBuf = pPg; p->page.pExtra = &p[1]; p->isBulkLocal = 0; @@ -480,9 +479,6 @@ static void pcache1FreePage(PgHdr1 *p){ pCache->pFree = p; }else{ pcache1Free(p->page.pBuf); -#ifdef SQLITE_PCACHE_SEPARATE_HEADER - sqlite3_free(p); -#endif } (*pCache->pnPurgeable)--; } @@ -1129,7 +1125,7 @@ static void pcache1Rekey( assert( iOld!=iNew ); /* The page number really is changing */ pcache1EnterMutex(pCache->pGroup); - + assert( pcache1FetchNoMutex(p, iOld, 0)==pPage ); /* pPg really is iOld */ hOld = iOld%pCache->nHash; pp = &pCache->apHash[hOld]; @@ -1249,9 +1245,6 @@ int sqlite3PcacheReleaseMemory(int nReq){ && p->isAnchor==0 ){ nFree += pcache1MemSize(p->page.pBuf); -#ifdef SQLITE_PCACHE_SEPARATE_HEADER - nFree += sqlite3MemSize(p); -#endif assert( PAGE_IS_UNPINNED(p) ); pcache1PinPage(p); pcache1RemoveFromHash(p, 1); |