**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements that page cache.
**
** @(#) $Id: pcache.c,v 1.8 2008/08/22 16:22:17 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** A complete page cache is an instance of this structure.
*/
struct PCache {
................................................................................
  assert( !pcache.pStart );
  assert( p->apSave[0]==0 );
  assert( p->apSave[1]==0 );
  assert( p && p->pCache );
  return sqlite3MallocSize(p);
}









static PgHdr *pcacheRecycle(PCache *pCache){
  PgHdr *p = 0;

  assert( pcache.isInit );
  assert( sqlite3_mutex_held(pcache.mutex_lru) );

  p = pcache.pLruSynced;
  if( !p ){
    p = pcache.pLruTail;
  }
  if( p && (p->flags&PGHDR_DIRTY) ){
    if( SQLITE_OK==sqlite3_mutex_try(pcache.mutex_mem2) ){
      int iInUseDB;
      PCache *pC = p->pCache;

      if( pCache==pC ){
        /* If trying to recycle a page from pCache, then set the iInUseDb
        ** flag to zero. This is done so that the sqlite3PcacheSetFlags()
        ** can tell that the LRU mutex is already held.
        **
        ** It is quite safe to modify the iInUseDB variable, because we 
        ** know no other thread will attempt to use pCache (because this
        ** call is being made from within a call to sqlite3PcacheFetch()
        ** on pCache). 
        */
        assert( pCache->iInUseDB );
        iInUseDB = pCache->iInUseDB;
        pCache->iInUseDB = 0;
      }

      assert( pC->iInUseMM==0 );
      pC->iInUseMM = 1;
      if( pC->xStress && pC->iInUseDB==0 ){

        pC->xStress(pC->pStress, p);
      }
      if( pCache==pC ){
        pCache->iInUseDB = iInUseDB;

      }
      pC->iInUseMM = 0;
      sqlite3_mutex_leave(pcache.mutex_mem2);
    }
  }
  if( p && (p->flags&PGHDR_DIRTY) ){
    p = 0;
................................................................................
*/
void sqlite3PcacheMakeClean(PgHdr *p){
  PCache *pCache;
  assert( p->pCache->iInUseDB || p->pCache->iInUseMM );
  if( (p->flags & PGHDR_DIRTY)==0 ) return;
  assert( p->apSave[0]==0 && p->apSave[1]==0 );
  assert( p->flags & PGHDR_DIRTY );
  assert( p->nRef>0 || sqlite3_mutex_held(pcache.mutex_lru) );
  pCache = p->pCache;
  pcacheRemoveFromList(&pCache->pDirty, p);
  pcacheAddToList(&pCache->pClean, p);
  p->flags &= ~PGHDR_DIRTY;
}

/*
................................................................................
*/
void sqlite3PcacheSetFlags(PCache *pCache, int andMask, int orMask){
  PgHdr *p;

  assert( (orMask&PGHDR_NEED_SYNC)==0 );
  assert( pCache->iInUseDB || pCache->iInUseMM );

  /* If this call is being made from within a call to the xStress callback
  ** of a pager-cache (i.e. from within pagerRecycle()), then the 
  ** PCache.iInUseDB will be set to zero. In this case, the LRU mutex is
  ** already held. Otherwise, obtain it before modifying any PgHdr.flags
  ** variables or traversing the LRU list.
  */ 
  if( pCache->iInUseDB ){
    pcacheEnterGlobal();
  }
  assert( sqlite3_mutex_held(pcache.mutex_lru) );

  for(p=pCache->pDirty; p; p=p->pNext){
    p->flags = (p->flags&andMask)|orMask;
  }
  for(p=pCache->pClean; p; p=p->pNext){
    p->flags = (p->flags&andMask)|orMask;
................................................................................
  }

  if( 0==(andMask&PGHDR_NEED_SYNC) ){
    for(p=pcache.pLruTail; p && (p->flags&PGHDR_NEED_SYNC); p=p->pPrevLru);
    pcache.pLruSynced = p;
  }

  if( pCache->iInUseDB ){
    pcacheExitGlobal();
  }
}

/*
** Set the suggested cache-size value.
*/
int sqlite3PcacheGetCachesize(PCache *pCache){
  return pCache->nMax;

**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements that page cache.
**
** @(#) $Id: pcache.c,v 1.9 2008/08/22 17:09:50 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** A complete page cache is an instance of this structure.
*/
struct PCache {
................................................................................
  assert( !pcache.pStart );
  assert( p->apSave[0]==0 );
  assert( p->apSave[1]==0 );
  assert( p && p->pCache );
  return sqlite3MallocSize(p);
}

/*
** Recycle a page from the global LRU list. If no page can be recycled, 
** return NULL. Otherwise, the pointer returned points to a PgHdr 
** object that has been removed from all lists and hash tables in
** which is was referenced. The caller may reuse the allocation directly
** or may pass it to pcachePageFree() to return the memory to the heap
** (or pcache.pFree list).
*/ 
static PgHdr *pcacheRecycle(PCache *pCache){
  PgHdr *p = 0;

  assert( pcache.isInit );
  assert( sqlite3_mutex_held(pcache.mutex_lru) );

  p = pcache.pLruSynced;
  if( !p ){
    p = pcache.pLruTail;
  }
  if( p && (p->flags&PGHDR_DIRTY) ){
    if( SQLITE_OK==sqlite3_mutex_try(pcache.mutex_mem2) ){

      PCache *pC = p->pCache;
















      assert( pC->iInUseMM==0 );
      pC->iInUseMM = 1;
      if( pC->xStress && (pC->iInUseDB==0 || pC==pCache) ){
        pcacheExitGlobal();
        pC->xStress(pC->pStress, p);



        pcacheEnterGlobal();
      }
      pC->iInUseMM = 0;
      sqlite3_mutex_leave(pcache.mutex_mem2);
    }
  }
  if( p && (p->flags&PGHDR_DIRTY) ){
    p = 0;
................................................................................
*/
void sqlite3PcacheMakeClean(PgHdr *p){
  PCache *pCache;
  assert( p->pCache->iInUseDB || p->pCache->iInUseMM );
  if( (p->flags & PGHDR_DIRTY)==0 ) return;
  assert( p->apSave[0]==0 && p->apSave[1]==0 );
  assert( p->flags & PGHDR_DIRTY );

  pCache = p->pCache;
  pcacheRemoveFromList(&pCache->pDirty, p);
  pcacheAddToList(&pCache->pClean, p);
  p->flags &= ~PGHDR_DIRTY;
}

/*
................................................................................
*/
void sqlite3PcacheSetFlags(PCache *pCache, int andMask, int orMask){
  PgHdr *p;

  assert( (orMask&PGHDR_NEED_SYNC)==0 );
  assert( pCache->iInUseDB || pCache->iInUseMM );




  /* Obtain the global mutex before modifying any PgHdr.flags variables 
  ** or traversing the LRU list.
  */ 

  pcacheEnterGlobal();

  assert( sqlite3_mutex_held(pcache.mutex_lru) );

  for(p=pCache->pDirty; p; p=p->pNext){
    p->flags = (p->flags&andMask)|orMask;
  }
  for(p=pCache->pClean; p; p=p->pNext){
    p->flags = (p->flags&andMask)|orMask;
................................................................................
  }

  if( 0==(andMask&PGHDR_NEED_SYNC) ){
    for(p=pcache.pLruTail; p && (p->flags&PGHDR_NEED_SYNC); p=p->pPrevLru);
    pcache.pLruSynced = p;
  }


  pcacheExitGlobal();

}

/*
** Set the suggested cache-size value.
*/
int sqlite3PcacheGetCachesize(PCache *pCache){
  return pCache->nMax;