/*
** If there are currently more than pcache.nMaxPage pages allocated, try
** to recycle pages to reduce the number allocated to pcache.nMaxPage.
*/
static void pcacheEnforceMaxPage() {
PgHdr *p;
assert( sqlite3_mutex_held(pcache.mutex) );
while( pcache.nCurrentPage>pcache.nMaxPage && (p = pcacheRecyclePage()) ) {
pcachePageFree(p);
}
}
/*
** Obtain space for a page. Try to recycle an old page if the limit on the
** number of pages has been reached. If the limit has not been reached or
** there are no pages eligible for recycling, allocate a new page.
**
** Return a pointer to the new page, or NULL if an OOM condition occurs.
*/
static int pcacheRecycleOrAlloc(PCache *pCache, PgHdr **ppPage) {
PgHdr *p = 0;
int szPage = pCache->szPage;
int szExtra = pCache->szExtra;
assert( pcache.isInit );
assert( sqlite3_mutex_held(pcache.mutex) );
*ppPage = 0;
/* If we have reached the limit for pinned/dirty pages, and there is at
** least one dirty page, invoke the xStress callback to cause a page to
** become clean.
*/
expensive_assert( pCache->nPinned==pcachePinnedCount(pCache) );
expensive_assert( pcacheCheckSynced(pCache) );
if( pCache->xStress
&& pCache->pDirty
&& pCache->nPinned>=(pcache.nMaxPage+pCache->nMin-pcache.nMinPage)
) {
PgHdr *pPg;
assert(pCache->pDirtyTail);
for(pPg=pCache->pSynced;
pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC));
pPg=pPg->pPrev
);
if( !pPg ) {
for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pPrev);
}
if( pPg ) {
int rc;
pcacheExitMutex();
rc = pCache->xStress(pCache->pStress, pPg);
pcacheEnterMutex();
if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ) {
return rc;
}
}
}
/* If the global page limit has been reached, try to recycle a page. */
if( pCache->bPurgeable && pcache.nCurrentPage>=pcache.nMaxPage ) {
p = pcacheRecyclePage();
}
/* If a page has been recycled but it is the wrong size, free it. */
if( p && (p->pCache->szPage!=szPage || p->pCache->szPage!=szExtra) ) {
pcachePageFree(p);
p = 0;
}
if( !p ) {
p = pcachePageAlloc(pCache);
}
*ppPage = p;
return (p?SQLITE_OK:SQLITE_NOMEM);
}
/*
** This function is called to free superfluous dynamically allocated memory
** held by the pager system. Memory in use by any SQLite pager allocated
** by the current thread may be sqlite3_free()ed.
**
** nReq is the number of bytes of memory required. Once this much has
** been released, the function returns. The return value is the total number
** of bytes of memory released.
*/
int sqlite3PcacheReleaseMemory(int nReq){
int nFree = 0;
if( pcache_g.pStart==0 ){
PgHdr *p;
pcacheEnterMutex();
while( (nReq<0 || nFree<nReq) && (p=pcacheRecyclePage()) ){
nFree += pcachePageSize(p);
pcachePageFree(p);
}
pcacheExitMutex();
}
return nFree;
}
