SQLITE_THREADSAFE==1,      /* bFullMutex */
   SQLITE_USE_URI,            /* bOpenUri */
   0x7ffffffe,                /* mxStrlen */
   128,                       /* szLookaside */
   500,                       /* nLookaside */
   {0,0,0,0,0,0,0,0},         /* m */
   {0,0,0,0,0,0,0,0,0},       /* mutex */
   {0,0,0,0,0,0,0,0,0,0,0},   /* pcache */
   (void*)0,                  /* pHeap */
   0,                         /* nHeap */
   0, 0,                      /* mnHeap, mxHeap */
   (void*)0,                  /* pScratch */
   0,                         /* szScratch */
   0,                         /* nScratch */
   (void*)0,                  /* pPage */

   SQLITE_THREADSAFE==1,      /* bFullMutex */
   SQLITE_USE_URI,            /* bOpenUri */
   0x7ffffffe,                /* mxStrlen */
   128,                       /* szLookaside */
   500,                       /* nLookaside */
   {0,0,0,0,0,0,0,0},         /* m */
   {0,0,0,0,0,0,0,0,0},       /* mutex */
   {0,0,0,0,0,0,0,0,0,0,0},   /* pcache2 */
   (void*)0,                  /* pHeap */
   0,                         /* nHeap */
   0, 0,                      /* mnHeap, mxHeap */
   (void*)0,                  /* pScratch */
   0,                         /* szScratch */
   0,                         /* nScratch */
   (void*)0,                  /* pPage */

      sqlite3GlobalConfig.pPage = va_arg(ap, void*);
      sqlite3GlobalConfig.szPage = va_arg(ap, int);
      sqlite3GlobalConfig.nPage = va_arg(ap, int);
      break;
    }

    case SQLITE_CONFIG_PCACHE: {










      /* Specify an alternative page cache implementation */
      sqlite3GlobalConfig.pcache = *va_arg(ap, sqlite3_pcache_methods*);
      break;
    }

    case SQLITE_CONFIG_GETPCACHE: {
      if( sqlite3GlobalConfig.pcache.xInit==0 ){
        sqlite3PCacheSetDefault();
      }
      *va_arg(ap, sqlite3_pcache_methods*) = sqlite3GlobalConfig.pcache;
      break;
    }

#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
    case SQLITE_CONFIG_HEAP: {
      /* Designate a buffer for heap memory space */
      sqlite3GlobalConfig.pHeap = va_arg(ap, void*);

      sqlite3GlobalConfig.pPage = va_arg(ap, void*);
      sqlite3GlobalConfig.szPage = va_arg(ap, int);
      sqlite3GlobalConfig.nPage = va_arg(ap, int);
      break;
    }

    case SQLITE_CONFIG_PCACHE: {
      /* no-op */
      break;
    }
    case SQLITE_CONFIG_GETPCACHE: {
      /* now an error */
      rc = SQLITE_ERROR;
      break;
    }

    case SQLITE_CONFIG_PCACHE2: {
      /* Specify an alternative page cache implementation */
      sqlite3GlobalConfig.pcache2 = *va_arg(ap, sqlite3_pcache_methods2*);
      break;
    }

    case SQLITE_CONFIG_GETPCACHE2: {
      if( sqlite3GlobalConfig.pcache2.xInit==0 ){
        sqlite3PCacheSetDefault();
      }
      *va_arg(ap, sqlite3_pcache_methods2*) = sqlite3GlobalConfig.pcache2;
      break;
    }

#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
    case SQLITE_CONFIG_HEAP: {
      /* Designate a buffer for heap memory space */
      sqlite3GlobalConfig.pHeap = va_arg(ap, void*);

*/
static void pcacheUnpin(PgHdr *p){
  PCache *pCache = p->pCache;
  if( pCache->bPurgeable ){
    if( p->pgno==1 ){
      pCache->pPage1 = 0;
    }
    sqlite3GlobalConfig.pcache.xUnpin(pCache->pCache, p, 0);
  }
}

/*************************************************** General Interfaces ******
**
** Initialize and shutdown the page cache subsystem. Neither of these 
** functions are threadsafe.
*/
int sqlite3PcacheInitialize(void){
  if( sqlite3GlobalConfig.pcache.xInit==0 ){
    /* IMPLEMENTATION-OF: R-26801-64137 If the xInit() method is NULL, then the
    ** built-in default page cache is used instead of the application defined
    ** page cache. */
    sqlite3PCacheSetDefault();
  }
  return sqlite3GlobalConfig.pcache.xInit(sqlite3GlobalConfig.pcache.pArg);
}
void sqlite3PcacheShutdown(void){
  if( sqlite3GlobalConfig.pcache.xShutdown ){
    /* IMPLEMENTATION-OF: R-26000-56589 The xShutdown() method may be NULL. */
    sqlite3GlobalConfig.pcache.xShutdown(sqlite3GlobalConfig.pcache.pArg);
  }
}

/*
** Return the size in bytes of a PCache object.
*/
int sqlite3PcacheSize(void){ return sizeof(PCache); }
................................................................................
/*
** Change the page size for PCache object. The caller must ensure that there
** are no outstanding page references when this function is called.
*/
void sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
  assert( pCache->nRef==0 && pCache->pDirty==0 );
  if( pCache->pCache ){
    sqlite3GlobalConfig.pcache.xDestroy(pCache->pCache);
    pCache->pCache = 0;
    pCache->pPage1 = 0;
  }
  pCache->szPage = szPage;
}

/*
................................................................................
*/
int sqlite3PcacheFetch(
  PCache *pCache,       /* Obtain the page from this cache */
  Pgno pgno,            /* Page number to obtain */
  int createFlag,       /* If true, create page if it does not exist already */
  PgHdr **ppPage        /* Write the page here */
){

  PgHdr *pPage = 0;
  int eCreate;

  assert( pCache!=0 );
  assert( createFlag==1 || createFlag==0 );
  assert( pgno>0 );

  /* If the pluggable cache (sqlite3_pcache*) has not been allocated,
  ** allocate it now.
  */
  if( !pCache->pCache && createFlag ){
    sqlite3_pcache *p;
    int nByte;
    nByte = pCache->szPage + pCache->szExtra + sizeof(PgHdr);
    p = sqlite3GlobalConfig.pcache.xCreate(nByte, pCache->bPurgeable);
    if( !p ){
      return SQLITE_NOMEM;
    }
    sqlite3GlobalConfig.pcache.xCachesize(p, pCache->nMax);
    pCache->pCache = p;
  }

  eCreate = createFlag * (1 + (!pCache->bPurgeable || !pCache->pDirty));
  if( pCache->pCache ){
    pPage = sqlite3GlobalConfig.pcache.xFetch(pCache->pCache, pgno, eCreate);
  }

  if( !pPage && eCreate==1 ){
    PgHdr *pPg;

    /* Find a dirty page to write-out and recycle. First try to find a 
    ** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
................................................................................
#endif
      rc = pCache->xStress(pCache->pStress, pPg);
      if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
        return rc;
      }
    }

    pPage = sqlite3GlobalConfig.pcache.xFetch(pCache->pCache, pgno, 2);
  }

  if( pPage ){
    if( !pPage->pData ){


      memset(pPage, 0, sizeof(PgHdr));


      pPage->pData = (void *)&pPage[1];
      pPage->pExtra = (void*)&((char *)pPage->pData)[pCache->szPage];
      memset(pPage->pExtra, 0, pCache->szExtra);
      pPage->pCache = pCache;
      pPage->pgno = pgno;
    }
    assert( pPage->pCache==pCache );
    assert( pPage->pgno==pgno );
    assert( pPage->pData==(void *)&pPage[1] );
    assert( pPage->pExtra==(void *)&((char *)&pPage[1])[pCache->szPage] );



    if( 0==pPage->nRef ){
      pCache->nRef++;
    }
    pPage->nRef++;
    if( pgno==1 ){
      pCache->pPage1 = pPage;
    }
  }
  *ppPage = pPage;
  return (pPage==0 && eCreate) ? SQLITE_NOMEM : SQLITE_OK;
}

/*
** Decrement the reference count on a page. If the page is clean and the
** reference count drops to 0, then it is made elible for recycling.
*/
void sqlite3PcacheRelease(PgHdr *p){
................................................................................
    pcacheRemoveFromDirtyList(p);
  }
  pCache = p->pCache;
  pCache->nRef--;
  if( p->pgno==1 ){
    pCache->pPage1 = 0;
  }
  sqlite3GlobalConfig.pcache.xUnpin(pCache->pCache, p, 1);
}

/*
** Make sure the page is marked as dirty. If it isn't dirty already,
** make it so.
*/
void sqlite3PcacheMakeDirty(PgHdr *p){
................................................................................
/*
** Change the page number of page p to newPgno. 
*/
void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
  PCache *pCache = p->pCache;
  assert( p->nRef>0 );
  assert( newPgno>0 );
  sqlite3GlobalConfig.pcache.xRekey(pCache->pCache, p, p->pgno, newPgno);
  p->pgno = newPgno;
  if( (p->flags&PGHDR_DIRTY) && (p->flags&PGHDR_NEED_SYNC) ){
    pcacheRemoveFromDirtyList(p);
    pcacheAddToDirtyList(p);
  }
}

................................................................................
        sqlite3PcacheMakeClean(p);
      }
    }
    if( pgno==0 && pCache->pPage1 ){
      memset(pCache->pPage1->pData, 0, pCache->szPage);
      pgno = 1;
    }
    sqlite3GlobalConfig.pcache.xTruncate(pCache->pCache, pgno+1);
  }
}

/*
** Close a cache.
*/
void sqlite3PcacheClose(PCache *pCache){
  if( pCache->pCache ){
    sqlite3GlobalConfig.pcache.xDestroy(pCache->pCache);
  }
}

/* 
** Discard the contents of the cache.
*/
void sqlite3PcacheClear(PCache *pCache){
................................................................................

/* 
** Return the total number of pages in the cache.
*/
int sqlite3PcachePagecount(PCache *pCache){
  int nPage = 0;
  if( pCache->pCache ){
    nPage = sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache);
  }
  return nPage;
}

#ifdef SQLITE_TEST
/*
** Get the suggested cache-size value.
................................................................................

/*
** Set the suggested cache-size value.
*/
void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
  pCache->nMax = mxPage;
  if( pCache->pCache ){
    sqlite3GlobalConfig.pcache.xCachesize(pCache->pCache, mxPage);
  }
}

#if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
/*
** For all dirty pages currently in the cache, invoke the specified
** callback. This is only used if the SQLITE_CHECK_PAGES macro is

*/
static void pcacheUnpin(PgHdr *p){
  PCache *pCache = p->pCache;
  if( pCache->bPurgeable ){
    if( p->pgno==1 ){
      pCache->pPage1 = 0;
    }
    sqlite3GlobalConfig.pcache2.xUnpin(pCache->pCache, p->pPage, 0);
  }
}

/*************************************************** General Interfaces ******
**
** Initialize and shutdown the page cache subsystem. Neither of these 
** functions are threadsafe.
*/
int sqlite3PcacheInitialize(void){
  if( sqlite3GlobalConfig.pcache2.xInit==0 ){
    /* IMPLEMENTATION-OF: R-26801-64137 If the xInit() method is NULL, then the
    ** built-in default page cache is used instead of the application defined
    ** page cache. */
    sqlite3PCacheSetDefault();
  }
  return sqlite3GlobalConfig.pcache2.xInit(sqlite3GlobalConfig.pcache2.pArg);
}
void sqlite3PcacheShutdown(void){
  if( sqlite3GlobalConfig.pcache2.xShutdown ){
    /* IMPLEMENTATION-OF: R-26000-56589 The xShutdown() method may be NULL. */
    sqlite3GlobalConfig.pcache2.xShutdown(sqlite3GlobalConfig.pcache2.pArg);
  }
}

/*
** Return the size in bytes of a PCache object.
*/
int sqlite3PcacheSize(void){ return sizeof(PCache); }
................................................................................
/*
** Change the page size for PCache object. The caller must ensure that there
** are no outstanding page references when this function is called.
*/
void sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
  assert( pCache->nRef==0 && pCache->pDirty==0 );
  if( pCache->pCache ){
    sqlite3GlobalConfig.pcache2.xDestroy(pCache->pCache);
    pCache->pCache = 0;
    pCache->pPage1 = 0;
  }
  pCache->szPage = szPage;
}

/*
................................................................................
*/
int sqlite3PcacheFetch(
  PCache *pCache,       /* Obtain the page from this cache */
  Pgno pgno,            /* Page number to obtain */
  int createFlag,       /* If true, create page if it does not exist already */
  PgHdr **ppPage        /* Write the page here */
){
  sqlite3_pcache_page *pPage = 0;
  PgHdr *pPgHdr = 0;
  int eCreate;

  assert( pCache!=0 );
  assert( createFlag==1 || createFlag==0 );
  assert( pgno>0 );

  /* If the pluggable cache (sqlite3_pcache*) has not been allocated,
  ** allocate it now.
  */
  if( !pCache->pCache && createFlag ){
    sqlite3_pcache *p;
    p = sqlite3GlobalConfig.pcache2.xCreate(
        pCache->szExtra + sizeof(PgHdr), pCache->szPage, pCache->bPurgeable
    );
    if( !p ){
      return SQLITE_NOMEM;
    }
    sqlite3GlobalConfig.pcache2.xCachesize(p, pCache->nMax);
    pCache->pCache = p;
  }

  eCreate = createFlag * (1 + (!pCache->bPurgeable || !pCache->pDirty));
  if( pCache->pCache ){
    pPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
  }

  if( !pPage && eCreate==1 ){
    PgHdr *pPg;

    /* Find a dirty page to write-out and recycle. First try to find a 
    ** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
................................................................................
#endif
      rc = pCache->xStress(pCache->pStress, pPg);
      if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
        return rc;
      }
    }

    pPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
  }

  if( pPage ){
    pPgHdr = (PgHdr *)pPage->pExtra;

    if( !pPgHdr->pPage ){
      memset(pPgHdr, 0, sizeof(PgHdr));
      pPgHdr->pPage = pPage;
      pPgHdr->pData = pPage->pBuf;
      pPgHdr->pExtra = (void *)&pPgHdr[1];

      memset(pPgHdr->pExtra, 0, pCache->szExtra);
      pPgHdr->pCache = pCache;
      pPgHdr->pgno = pgno;
    }
    assert( pPgHdr->pCache==pCache );
    assert( pPgHdr->pgno==pgno );


    assert( pPgHdr->pData==pPage->pBuf );
    assert( pPgHdr->pExtra==(void *)&pPgHdr[1] );

    if( 0==pPgHdr->nRef ){
      pCache->nRef++;
    }
    pPgHdr->nRef++;
    if( pgno==1 ){
      pCache->pPage1 = pPgHdr;
    }
  }
  *ppPage = pPgHdr;
  return (pPgHdr==0 && eCreate) ? SQLITE_NOMEM : SQLITE_OK;
}

/*
** Decrement the reference count on a page. If the page is clean and the
** reference count drops to 0, then it is made elible for recycling.
*/
void sqlite3PcacheRelease(PgHdr *p){
................................................................................
    pcacheRemoveFromDirtyList(p);
  }
  pCache = p->pCache;
  pCache->nRef--;
  if( p->pgno==1 ){
    pCache->pPage1 = 0;
  }
  sqlite3GlobalConfig.pcache2.xUnpin(pCache->pCache, p->pPage, 1);
}

/*
** Make sure the page is marked as dirty. If it isn't dirty already,
** make it so.
*/
void sqlite3PcacheMakeDirty(PgHdr *p){
................................................................................
/*
** Change the page number of page p to newPgno. 
*/
void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
  PCache *pCache = p->pCache;
  assert( p->nRef>0 );
  assert( newPgno>0 );
  sqlite3GlobalConfig.pcache2.xRekey(pCache->pCache, p->pPage, p->pgno,newPgno);
  p->pgno = newPgno;
  if( (p->flags&PGHDR_DIRTY) && (p->flags&PGHDR_NEED_SYNC) ){
    pcacheRemoveFromDirtyList(p);
    pcacheAddToDirtyList(p);
  }
}

................................................................................
        sqlite3PcacheMakeClean(p);
      }
    }
    if( pgno==0 && pCache->pPage1 ){
      memset(pCache->pPage1->pData, 0, pCache->szPage);
      pgno = 1;
    }
    sqlite3GlobalConfig.pcache2.xTruncate(pCache->pCache, pgno+1);
  }
}

/*
** Close a cache.
*/
void sqlite3PcacheClose(PCache *pCache){
  if( pCache->pCache ){
    sqlite3GlobalConfig.pcache2.xDestroy(pCache->pCache);
  }
}

/* 
** Discard the contents of the cache.
*/
void sqlite3PcacheClear(PCache *pCache){
................................................................................

/* 
** Return the total number of pages in the cache.
*/
int sqlite3PcachePagecount(PCache *pCache){
  int nPage = 0;
  if( pCache->pCache ){
    nPage = sqlite3GlobalConfig.pcache2.xPagecount(pCache->pCache);
  }
  return nPage;
}

#ifdef SQLITE_TEST
/*
** Get the suggested cache-size value.
................................................................................

/*
** Set the suggested cache-size value.
*/
void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
  pCache->nMax = mxPage;
  if( pCache->pCache ){
    sqlite3GlobalConfig.pcache2.xCachesize(pCache->pCache, mxPage);
  }
}

#if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
/*
** For all dirty pages currently in the cache, invoke the specified
** callback. This is only used if the SQLITE_CHECK_PAGES macro is

typedef struct PCache PCache;

/*
** Every page in the cache is controlled by an instance of the following
** structure.
*/
struct PgHdr {

  void *pData;                   /* Content of this page */
  void *pExtra;                  /* Extra content */
  PgHdr *pDirty;                 /* Transient list of dirty pages */
  Pgno pgno;                     /* Page number for this page */
  Pager *pPager;                 /* The pager this page is part of */
#ifdef SQLITE_CHECK_PAGES
  u32 pageHash;                  /* Hash of page content */
#endif

typedef struct PCache PCache;

/*
** Every page in the cache is controlled by an instance of the following
** structure.
*/
struct PgHdr {
  sqlite3_pcache_page *pPage;    /* Pcache object page handle */
  void *pData;                   /* Page data */
  void *pExtra;                  /* Extra content */
  PgHdr *pDirty;                 /* Transient list of dirty pages */
  Pgno pgno;                     /* Page number for this page */
  Pager *pPager;                 /* The pager this page is part of */
#ifdef SQLITE_CHECK_PAGES
  u32 pageHash;                  /* Hash of page content */
#endif

  /* Cache configuration parameters. Page size (szPage) and the purgeable
  ** flag (bPurgeable) are set when the cache is created. nMax may be 
  ** modified at any time by a call to the pcache1CacheSize() method.
  ** The PGroup mutex must be held when accessing nMax.
  */
  PGroup *pGroup;                     /* PGroup this cache belongs to */
  int szPage;                         /* Size of allocated pages in bytes */

  int bPurgeable;                     /* True if cache is purgeable */
  unsigned int nMin;                  /* Minimum number of pages reserved */
  unsigned int nMax;                  /* Configured "cache_size" value */
  unsigned int n90pct;                /* nMax*9/10 */

  /* Hash table of all pages. The following variables may only be accessed
  ** when the accessor is holding the PGroup mutex.
................................................................................
  PgHdr1 **apHash;                    /* Hash table for fast lookup by key */

  unsigned int iMaxKey;               /* Largest key seen since xTruncate() */
};

/*
** Each cache entry is represented by an instance of the following 

** structure. A buffer of PgHdr1.pCache->szPage bytes is allocated 
** directly before this structure in memory (see the PGHDR1_TO_PAGE() 
** macro below).
*/
struct PgHdr1 {

  unsigned int iKey;             /* Key value (page number) */
  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 */
};

................................................................................
/*
** All code in this file should access the global structure above via the
** alias "pcache1". This ensures that the WSD emulation is used when
** compiling for systems that do not support real WSD.
*/
#define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g))

/*
** When a PgHdr1 structure is allocated, the associated PCache1.szPage
** bytes of data are located directly before it in memory (i.e. the total
** size of the allocation is sizeof(PgHdr1)+PCache1.szPage byte). The
** PGHDR1_TO_PAGE() macro takes a pointer to a PgHdr1 structure as
** an argument and returns a pointer to the associated block of szPage
** bytes. The PAGE_TO_PGHDR1() macro does the opposite: its argument is
** a pointer to a block of szPage bytes of data and the return value is
** a pointer to the associated PgHdr1 structure.
**
**   assert( PGHDR1_TO_PAGE(PAGE_TO_PGHDR1(pCache, X))==X );
*/
#define PGHDR1_TO_PAGE(p)    (void*)(((char*)p) - p->pCache->szPage)
#define PAGE_TO_PGHDR1(c, p) (PgHdr1*)(((char*)p) + c->szPage)

/*
** Macros to enter and leave the PCache LRU mutex.
*/
#define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex)
#define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex)

/******************************************************************************/
................................................................................
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */

/*
** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache){
  int nByte = sizeof(PgHdr1) + pCache->szPage;
  PgHdr1 *p = 0;
  void *pPg;

  /* The group mutex must be released before pcache1Alloc() is called. This
  ** is because it may call sqlite3_release_memory(), which assumes that 
  ** this mutex is not held. */
  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  pcache1LeaveMutex(pCache->pGroup);

  pPg = pcache1Alloc(nByte);










  pcache1EnterMutex(pCache->pGroup);

  if( pPg ){
    p = PAGE_TO_PGHDR1(pCache, pPg);

    if( pCache->bPurgeable ){
      pCache->pGroup->nCurrentPage++;
    }

  }
  return p;
}

/*
** Free a page object allocated by pcache1AllocPage().
**
** The pointer is allowed to be NULL, which is prudent.  But it turns out
** that the current implementation happens to never call this routine
** with a NULL pointer, so we mark the NULL test with ALWAYS().
*/
static void pcache1FreePage(PgHdr1 *p){
  if( ALWAYS(p) ){
    PCache1 *pCache = p->pCache;
    assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) );
    pcache1Free(PGHDR1_TO_PAGE(p));



    if( pCache->bPurgeable ){
      pCache->pGroup->nCurrentPage--;
    }
  }
}

/*
................................................................................
**
** Or, the heap is used for all page cache memory put the heap is
** under memory pressure, then again it is desirable to avoid
** allocating a new page cache entry in order to avoid stressing
** the heap even further.
*/
static int pcache1UnderMemoryPressure(PCache1 *pCache){
  if( pcache1.nSlot && pCache->szPage<=pcache1.szSlot ){
    return pcache1.bUnderPressure;
  }else{
    return sqlite3HeapNearlyFull();
  }
}

/******************************************************************************/
................................................................................
}

/*
** Implementation of the sqlite3_pcache.xCreate method.
**
** Allocate a new cache.
*/
static sqlite3_pcache *pcache1Create(int szPage, int bPurgeable){
  PCache1 *pCache;      /* The newly created page cache */
  PGroup *pGroup;       /* The group the new page cache will belong to */
  int sz;               /* Bytes of memory required to allocate the new cache */

  /*
  ** The seperateCache variable is true if each PCache has its own private
  ** PGroup.  In other words, separateCache is true for mode (1) where no
................................................................................
      pGroup = (PGroup*)&pCache[1];
      pGroup->mxPinned = 10;
    }else{
      pGroup = &pcache1.grp;
    }
    pCache->pGroup = pGroup;
    pCache->szPage = szPage;

    pCache->bPurgeable = (bPurgeable ? 1 : 0);
    if( bPurgeable ){
      pCache->nMin = 10;
      pcache1EnterMutex(pGroup);
      pGroup->nMinPage += pCache->nMin;
      pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
      pcache1LeaveMutex(pGroup);
................................................................................
**
**      then attempt to recycle a page from the LRU list. If it is the right
**      size, return the recycled buffer. Otherwise, free the buffer and
**      proceed to step 5. 
**
**   5. Otherwise, allocate and return a new page buffer.
*/

static void *pcache1Fetch(sqlite3_pcache *p, unsigned int iKey, int createFlag){



  int nPinned;
  PCache1 *pCache = (PCache1 *)p;
  PGroup *pGroup;
  PgHdr1 *pPage = 0;

  assert( pCache->bPurgeable || createFlag!=1 );
  assert( pCache->bPurgeable || pCache->nMin==0 );
................................................................................
  ** optimization:  The common case is to exit the module before reaching
  ** this point.
  */
#ifdef SQLITE_MUTEX_OMIT
  pGroup = pCache->pGroup;
#endif


  /* Step 3: Abort if createFlag is 1 but the cache is nearly full */
  nPinned = pCache->nPage - pCache->nRecyclable;
  assert( nPinned>=0 );
  assert( pGroup->mxPinned == pGroup->nMaxPage + 10 - pGroup->nMinPage );
  assert( pCache->n90pct == pCache->nMax*9/10 );
  if( createFlag==1 && (
        nPinned>=pGroup->mxPinned
................................................................................
      || pGroup->nCurrentPage>=pGroup->nMaxPage
      || pcache1UnderMemoryPressure(pCache)
  )){
    PCache1 *pOtherCache;
    pPage = pGroup->pLruTail;
    pcache1RemoveFromHash(pPage);
    pcache1PinPage(pPage);
    if( (pOtherCache = pPage->pCache)->szPage!=pCache->szPage ){


      pcache1FreePage(pPage);
      pPage = 0;
    }else{
      pGroup->nCurrentPage -= 
               (pOtherCache->bPurgeable - pCache->bPurgeable);
    }
  }

  /* Step 5. If a usable page buffer has still not been found, 
  ** attempt to allocate a new one. 
  */
  if( !pPage ){
................................................................................
    unsigned int h = iKey % pCache->nHash;
    pCache->nPage++;
    pPage->iKey = iKey;
    pPage->pNext = pCache->apHash[h];
    pPage->pCache = pCache;
    pPage->pLruPrev = 0;
    pPage->pLruNext = 0;
    *(void **)(PGHDR1_TO_PAGE(pPage)) = 0;
    pCache->apHash[h] = pPage;
  }

fetch_out:
  if( pPage && iKey>pCache->iMaxKey ){
    pCache->iMaxKey = iKey;
  }
  pcache1LeaveMutex(pGroup);
  return (pPage ? PGHDR1_TO_PAGE(pPage) : 0);
}


/*
** Implementation of the sqlite3_pcache.xUnpin method.
**
** Mark a page as unpinned (eligible for asynchronous recycling).
*/
static void pcache1Unpin(sqlite3_pcache *p, void *pPg, int reuseUnlikely){




  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = PAGE_TO_PGHDR1(pCache, pPg);
  PGroup *pGroup = pCache->pGroup;
 
  assert( pPage->pCache==pCache );
  pcache1EnterMutex(pGroup);

  /* It is an error to call this function if the page is already 
  ** part of the PGroup LRU list.
................................................................................
}

/*
** Implementation of the sqlite3_pcache.xRekey method. 
*/
static void pcache1Rekey(
  sqlite3_pcache *p,
  void *pPg,
  unsigned int iOld,
  unsigned int iNew
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = PAGE_TO_PGHDR1(pCache, pPg);
  PgHdr1 **pp;
  unsigned int h; 
  assert( pPage->iKey==iOld );
  assert( pPage->pCache==pCache );

  pcache1EnterMutex(pCache->pGroup);

................................................................................

/*
** This function is called during initialization (sqlite3_initialize()) to
** install the default pluggable cache module, assuming the user has not
** already provided an alternative.
*/
void sqlite3PCacheSetDefault(void){
  static const sqlite3_pcache_methods defaultMethods = {
    0,                       /* pArg */
    pcache1Init,             /* xInit */
    pcache1Shutdown,         /* xShutdown */
    pcache1Create,           /* xCreate */
    pcache1Cachesize,        /* xCachesize */
    pcache1Pagecount,        /* xPagecount */
    pcache1Fetch,            /* xFetch */
    pcache1Unpin,            /* xUnpin */
    pcache1Rekey,            /* xRekey */
    pcache1Truncate,         /* xTruncate */
    pcache1Destroy           /* xDestroy */
  };
  sqlite3_config(SQLITE_CONFIG_PCACHE, &defaultMethods);
}

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/*
** 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.
................................................................................
  int nFree = 0;
  assert( sqlite3_mutex_notheld(pcache1.grp.mutex) );
  assert( sqlite3_mutex_notheld(pcache1.mutex) );
  if( pcache1.pStart==0 ){
    PgHdr1 *p;
    pcache1EnterMutex(&pcache1.grp);
    while( (nReq<0 || nFree<nReq) && ((p=pcache1.grp.pLruTail)!=0) ){
      nFree += pcache1MemSize(PGHDR1_TO_PAGE(p));



      pcache1PinPage(p);
      pcache1RemoveFromHash(p);
      pcache1FreePage(p);
    }
    pcache1LeaveMutex(&pcache1.grp);
  }
  return nFree;

  /* Cache configuration parameters. Page size (szPage) and the purgeable
  ** flag (bPurgeable) are set when the cache is created. nMax may be 
  ** modified at any time by a call to the pcache1CacheSize() method.
  ** The PGroup mutex must be held when accessing nMax.
  */
  PGroup *pGroup;                     /* PGroup this cache belongs to */
  int szPage;                         /* Size of allocated pages in bytes */
  int szExtra;                        /* Size of extra space in bytes */
  int bPurgeable;                     /* True if cache is purgeable */
  unsigned int nMin;                  /* Minimum number of pages reserved */
  unsigned int nMax;                  /* Configured "cache_size" value */
  unsigned int n90pct;                /* nMax*9/10 */

  /* Hash table of all pages. The following variables may only be accessed
  ** when the accessor is holding the PGroup mutex.
................................................................................
  PgHdr1 **apHash;                    /* Hash table for fast lookup by key */

  unsigned int iMaxKey;               /* Largest key seen since xTruncate() */
};

/*
** 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.
*/
struct PgHdr1 {
  sqlite3_pcache_page page;
  unsigned int iKey;             /* Key value (page number) */
  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 */
};

................................................................................
/*
** All code in this file should access the global structure above via the
** alias "pcache1". This ensures that the WSD emulation is used when
** compiling for systems that do not support real WSD.
*/
#define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g))
















/*
** Macros to enter and leave the PCache LRU mutex.
*/
#define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex)
#define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex)

/******************************************************************************/
................................................................................
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */

/*
** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache){

  PgHdr1 *p = 0;
  void *pPg;

  /* The group mutex must be released before pcache1Alloc() is called. This
  ** is because it may call sqlite3_release_memory(), which assumes that 
  ** this mutex is not held. */
  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  pcache1LeaveMutex(pCache->pGroup);
#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(sizeof(PgHdr1) + pCache->szPage + pCache->szExtra);
  p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage];
#endif
  pcache1EnterMutex(pCache->pGroup);

  if( pPg ){
    p->page.pBuf = pPg;
    p->page.pExtra = &p[1];
    if( pCache->bPurgeable ){
      pCache->pGroup->nCurrentPage++;
    }
    return p;
  }
  return 0;
}

/*
** Free a page object allocated by pcache1AllocPage().
**
** The pointer is allowed to be NULL, which is prudent.  But it turns out
** that the current implementation happens to never call this routine
** with a NULL pointer, so we mark the NULL test with ALWAYS().
*/
static void pcache1FreePage(PgHdr1 *p){
  if( ALWAYS(p) ){
    PCache1 *pCache = p->pCache;
    assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) );
    pcache1Free(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
    sqlite3_free(p);
#endif
    if( pCache->bPurgeable ){
      pCache->pGroup->nCurrentPage--;
    }
  }
}

/*
................................................................................
**
** Or, the heap is used for all page cache memory put the heap is
** under memory pressure, then again it is desirable to avoid
** allocating a new page cache entry in order to avoid stressing
** the heap even further.
*/
static int pcache1UnderMemoryPressure(PCache1 *pCache){
  if( pcache1.nSlot && (pCache->szPage+pCache->szExtra)<=pcache1.szSlot ){
    return pcache1.bUnderPressure;
  }else{
    return sqlite3HeapNearlyFull();
  }
}

/******************************************************************************/
................................................................................
}

/*
** Implementation of the sqlite3_pcache.xCreate method.
**
** Allocate a new cache.
*/
static sqlite3_pcache *pcache1Create(int szExtra, int szPage, int bPurgeable){
  PCache1 *pCache;      /* The newly created page cache */
  PGroup *pGroup;       /* The group the new page cache will belong to */
  int sz;               /* Bytes of memory required to allocate the new cache */

  /*
  ** The seperateCache variable is true if each PCache has its own private
  ** PGroup.  In other words, separateCache is true for mode (1) where no
................................................................................
      pGroup = (PGroup*)&pCache[1];
      pGroup->mxPinned = 10;
    }else{
      pGroup = &pcache1.grp;
    }
    pCache->pGroup = pGroup;
    pCache->szPage = szPage;
    pCache->szExtra = szExtra;
    pCache->bPurgeable = (bPurgeable ? 1 : 0);
    if( bPurgeable ){
      pCache->nMin = 10;
      pcache1EnterMutex(pGroup);
      pGroup->nMinPage += pCache->nMin;
      pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
      pcache1LeaveMutex(pGroup);
................................................................................
**
**      then attempt to recycle a page from the LRU list. If it is the right
**      size, return the recycled buffer. Otherwise, free the buffer and
**      proceed to step 5. 
**
**   5. Otherwise, allocate and return a new page buffer.
*/
static sqlite3_pcache_page *pcache1Fetch(
  sqlite3_pcache *p, 
  unsigned int iKey, 
  int createFlag
){
  int nPinned;
  PCache1 *pCache = (PCache1 *)p;
  PGroup *pGroup;
  PgHdr1 *pPage = 0;

  assert( pCache->bPurgeable || createFlag!=1 );
  assert( pCache->bPurgeable || pCache->nMin==0 );
................................................................................
  ** optimization:  The common case is to exit the module before reaching
  ** this point.
  */
#ifdef SQLITE_MUTEX_OMIT
  pGroup = pCache->pGroup;
#endif


  /* Step 3: Abort if createFlag is 1 but the cache is nearly full */
  nPinned = pCache->nPage - pCache->nRecyclable;
  assert( nPinned>=0 );
  assert( pGroup->mxPinned == pGroup->nMaxPage + 10 - pGroup->nMinPage );
  assert( pCache->n90pct == pCache->nMax*9/10 );
  if( createFlag==1 && (
        nPinned>=pGroup->mxPinned
................................................................................
      || pGroup->nCurrentPage>=pGroup->nMaxPage
      || pcache1UnderMemoryPressure(pCache)
  )){
    PCache1 *pOtherCache;
    pPage = pGroup->pLruTail;
    pcache1RemoveFromHash(pPage);
    pcache1PinPage(pPage);
    if( (pOtherCache = pPage->pCache)->szPage!=pCache->szPage 
     || pOtherCache->szExtra!=pCache->szExtra 
    ){
      pcache1FreePage(pPage);
      pPage = 0;
    }else{

      pGroup->nCurrentPage -= (pOtherCache->bPurgeable - pCache->bPurgeable);
    }
  }

  /* Step 5. If a usable page buffer has still not been found, 
  ** attempt to allocate a new one. 
  */
  if( !pPage ){
................................................................................
    unsigned int h = iKey % pCache->nHash;
    pCache->nPage++;
    pPage->iKey = iKey;
    pPage->pNext = pCache->apHash[h];
    pPage->pCache = pCache;
    pPage->pLruPrev = 0;
    pPage->pLruNext = 0;
    *(void **)pPage->page.pExtra = 0;
    pCache->apHash[h] = pPage;
  }

fetch_out:
  if( pPage && iKey>pCache->iMaxKey ){
    pCache->iMaxKey = iKey;
  }
  pcache1LeaveMutex(pGroup);
  return &pPage->page;
}


/*
** Implementation of the sqlite3_pcache.xUnpin method.
**
** Mark a page as unpinned (eligible for asynchronous recycling).
*/
static void pcache1Unpin(
  sqlite3_pcache *p, 
  sqlite3_pcache_page *pPg, 
  int reuseUnlikely
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = (PgHdr1 *)pPg;
  PGroup *pGroup = pCache->pGroup;
 
  assert( pPage->pCache==pCache );
  pcache1EnterMutex(pGroup);

  /* It is an error to call this function if the page is already 
  ** part of the PGroup LRU list.
................................................................................
}

/*
** Implementation of the sqlite3_pcache.xRekey method. 
*/
static void pcache1Rekey(
  sqlite3_pcache *p,
  sqlite3_pcache_page *pPg,
  unsigned int iOld,
  unsigned int iNew
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = (PgHdr1 *)pPg;
  PgHdr1 **pp;
  unsigned int h; 
  assert( pPage->iKey==iOld );
  assert( pPage->pCache==pCache );

  pcache1EnterMutex(pCache->pGroup);

................................................................................

/*
** This function is called during initialization (sqlite3_initialize()) to
** install the default pluggable cache module, assuming the user has not
** already provided an alternative.
*/
void sqlite3PCacheSetDefault(void){
  static const sqlite3_pcache_methods2 defaultMethods = {
    0,                       /* pArg */
    pcache1Init,             /* xInit */
    pcache1Shutdown,         /* xShutdown */
    pcache1Create,           /* xCreate */
    pcache1Cachesize,        /* xCachesize */
    pcache1Pagecount,        /* xPagecount */
    pcache1Fetch,            /* xFetch */
    pcache1Unpin,            /* xUnpin */
    pcache1Rekey,            /* xRekey */
    pcache1Truncate,         /* xTruncate */
    pcache1Destroy           /* xDestroy */
  };
  sqlite3_config(SQLITE_CONFIG_PCACHE2, &defaultMethods);
}

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/*
** 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.
................................................................................
  int nFree = 0;
  assert( sqlite3_mutex_notheld(pcache1.grp.mutex) );
  assert( sqlite3_mutex_notheld(pcache1.mutex) );
  if( pcache1.pStart==0 ){
    PgHdr1 *p;
    pcache1EnterMutex(&pcache1.grp);
    while( (nReq<0 || nFree<nReq) && ((p=pcache1.grp.pLruTail)!=0) ){
      nFree += pcache1MemSize(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
      nFree += sqlite3MemSize(p);
#endif
      pcache1PinPage(p);
      pcache1RemoveFromHash(p);
      pcache1FreePage(p);
    }
    pcache1LeaveMutex(&pcache1.grp);
  }
  return nFree;

#define SQLITE_CONFIG_GETMUTEX     11  /* sqlite3_mutex_methods* */
/* previously SQLITE_CONFIG_CHUNKALLOC 12 which is now unused. */ 
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */
#define SQLITE_CONFIG_PCACHE       14  /* sqlite3_pcache_methods* */
#define SQLITE_CONFIG_GETPCACHE    15  /* sqlite3_pcache_methods* */
#define SQLITE_CONFIG_LOG          16  /* xFunc, void* */
#define SQLITE_CONFIG_URI          17  /* int */



/*
** CAPI3REF: Database Connection Configuration Options
**
** These constants are the available integer configuration options that
** can be passed as the second argument to the [sqlite3_db_config()] interface.
**
................................................................................
  int (*xPagecount)(sqlite3_pcache*);
  void *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
  void (*xUnpin)(sqlite3_pcache*, void*, int discard);
  void (*xRekey)(sqlite3_pcache*, void*, unsigned oldKey, unsigned newKey);
  void (*xTruncate)(sqlite3_pcache*, unsigned iLimit);
  void (*xDestroy)(sqlite3_pcache*);
};






















/*
** CAPI3REF: Online Backup Object
**
** The sqlite3_backup object records state information about an ongoing
** online backup operation.  ^The sqlite3_backup object is created by
** a call to [sqlite3_backup_init()] and is destroyed by a call to

#define SQLITE_CONFIG_GETMUTEX     11  /* sqlite3_mutex_methods* */
/* previously SQLITE_CONFIG_CHUNKALLOC 12 which is now unused. */ 
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */
#define SQLITE_CONFIG_PCACHE       14  /* sqlite3_pcache_methods* */
#define SQLITE_CONFIG_GETPCACHE    15  /* sqlite3_pcache_methods* */
#define SQLITE_CONFIG_LOG          16  /* xFunc, void* */
#define SQLITE_CONFIG_URI          17  /* int */
#define SQLITE_CONFIG_PCACHE2      18  /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_GETPCACHE2   19  /* sqlite3_pcache_methods2* */

/*
** CAPI3REF: Database Connection Configuration Options
**
** These constants are the available integer configuration options that
** can be passed as the second argument to the [sqlite3_db_config()] interface.
**
................................................................................
  int (*xPagecount)(sqlite3_pcache*);
  void *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
  void (*xUnpin)(sqlite3_pcache*, void*, int discard);
  void (*xRekey)(sqlite3_pcache*, void*, unsigned oldKey, unsigned newKey);
  void (*xTruncate)(sqlite3_pcache*, unsigned iLimit);
  void (*xDestroy)(sqlite3_pcache*);
};

typedef struct sqlite3_pcache_methods2 sqlite3_pcache_methods2;
typedef struct sqlite3_pcache_page sqlite3_pcache_page;
struct sqlite3_pcache_page {
  void *pBuf;
  void *pExtra;
};
struct sqlite3_pcache_methods2 {
  void *pArg;
  int (*xInit)(void*);
  void (*xShutdown)(void*);
  sqlite3_pcache *(*xCreate)(int szExtra, int szPage, int bPurgeable);
  void (*xCachesize)(sqlite3_pcache*, int nCachesize);
  int (*xPagecount)(sqlite3_pcache*);
  sqlite3_pcache_page *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
  void (*xUnpin)(sqlite3_pcache*, sqlite3_pcache_page*, int discard);
  void (*xRekey)(sqlite3_pcache*, sqlite3_pcache_page*, 
      unsigned oldKey, unsigned newKey);
  void (*xTruncate)(sqlite3_pcache*, unsigned iLimit);
  void (*xDestroy)(sqlite3_pcache*);
};

/*
** CAPI3REF: Online Backup Object
**
** The sqlite3_backup object records state information about an ongoing
** online backup operation.  ^The sqlite3_backup object is created by
** a call to [sqlite3_backup_init()] and is destroyed by a call to

  int bFullMutex;                   /* True to enable full mutexing */
  int bOpenUri;                     /* True to interpret filenames as URIs */
  int mxStrlen;                     /* Maximum string length */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
  sqlite3_pcache_methods pcache;    /* Low-level page-cache interface */
  void *pHeap;                      /* Heap storage space */
  int nHeap;                        /* Size of pHeap[] */
  int mnReq, mxReq;                 /* Min and max heap requests sizes */
  void *pScratch;                   /* Scratch memory */
  int szScratch;                    /* Size of each scratch buffer */
  int nScratch;                     /* Number of scratch buffers */
  void *pPage;                      /* Page cache memory */

  int bFullMutex;                   /* True to enable full mutexing */
  int bOpenUri;                     /* True to interpret filenames as URIs */
  int mxStrlen;                     /* Maximum string length */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
  sqlite3_pcache_methods2 pcache2;  /* Low-level page-cache interface */
  void *pHeap;                      /* Heap storage space */
  int nHeap;                        /* Size of pHeap[] */
  int mnReq, mxReq;                 /* Min and max heap requests sizes */
  void *pScratch;                   /* Scratch memory */
  int szScratch;                    /* Size of each scratch buffer */
  int nScratch;                     /* Number of scratch buffers */
  void *pPage;                      /* Page cache memory */

*/

#include "sqliteInt.h"
#include <string.h>
#include <tcl.h>

static struct Wrapped {
  sqlite3_pcache_methods pcache;
  sqlite3_mem_methods    mem;
  sqlite3_mutex_methods  mutex;

  int mem_init;                /* True if mem subsystem is initalized */
  int mem_fail;                /* True to fail mem subsystem inialization */
  int mutex_init;              /* True if mutex subsystem is initalized */
  int mutex_fail;              /* True to fail mutex subsystem inialization */
  int pcache_init;             /* True if pcache subsystem is initalized */
  int pcache_fail;             /* True to fail pcache subsystem inialization */
................................................................................
  return rc;
}
static void wrPCacheShutdown(void *pArg){
  wrapped.pcache.xShutdown(wrapped.pcache.pArg);
  wrapped.pcache_init = 0;
}

static sqlite3_pcache *wrPCacheCreate(int a, int b){
  return wrapped.pcache.xCreate(a, b);
}  
static void wrPCacheCachesize(sqlite3_pcache *p, int n){
  wrapped.pcache.xCachesize(p, n);
}  
static int wrPCachePagecount(sqlite3_pcache *p){
  return wrapped.pcache.xPagecount(p);
}  
static void *wrPCacheFetch(sqlite3_pcache *p, unsigned a, int b){
  return wrapped.pcache.xFetch(p, a, b);
}  
static void wrPCacheUnpin(sqlite3_pcache *p, void *a, int b){
  wrapped.pcache.xUnpin(p, a, b);
}  
static void wrPCacheRekey(sqlite3_pcache *p, void *a, unsigned b, unsigned c){





  wrapped.pcache.xRekey(p, a, b, c);
}  
static void wrPCacheTruncate(sqlite3_pcache *p, unsigned a){
  wrapped.pcache.xTruncate(p, a);
}  
static void wrPCacheDestroy(sqlite3_pcache *p){
  wrapped.pcache.xDestroy(p);
................................................................................

static void installInitWrappers(void){
  sqlite3_mutex_methods mutexmethods = {
    wrMutexInit,  wrMutexEnd,   wrMutexAlloc,
    wrMutexFree,  wrMutexEnter, wrMutexTry,
    wrMutexLeave, wrMutexHeld,  wrMutexNotheld
  };
  sqlite3_pcache_methods pcachemethods = {
    0,
    wrPCacheInit,      wrPCacheShutdown,  wrPCacheCreate, 
    wrPCacheCachesize, wrPCachePagecount, wrPCacheFetch,
    wrPCacheUnpin,     wrPCacheRekey,     wrPCacheTruncate,  
    wrPCacheDestroy
  };
  sqlite3_mem_methods memmethods = {
................................................................................
  };

  memset(&wrapped, 0, sizeof(wrapped));

  sqlite3_shutdown();
  sqlite3_config(SQLITE_CONFIG_GETMUTEX, &wrapped.mutex);
  sqlite3_config(SQLITE_CONFIG_GETMALLOC, &wrapped.mem);
  sqlite3_config(SQLITE_CONFIG_GETPCACHE, &wrapped.pcache);
  sqlite3_config(SQLITE_CONFIG_MUTEX, &mutexmethods);
  sqlite3_config(SQLITE_CONFIG_MALLOC, &memmethods);
  sqlite3_config(SQLITE_CONFIG_PCACHE, &pcachemethods);
}

static int init_wrapper_install(
  ClientData clientData, /* Unused */
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int objc,              /* Number of arguments */
  Tcl_Obj *CONST objv[]  /* Command arguments */
................................................................................
    return TCL_ERROR;
  }

  memset(&wrapped, 0, sizeof(&wrapped));
  sqlite3_shutdown();
  sqlite3_config(SQLITE_CONFIG_MUTEX, &wrapped.mutex);
  sqlite3_config(SQLITE_CONFIG_MALLOC, &wrapped.mem);
  sqlite3_config(SQLITE_CONFIG_PCACHE, &wrapped.pcache);
  return TCL_OK;
}

static int init_wrapper_clear(
  ClientData clientData, /* Unused */
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int objc,              /* Number of arguments */

*/

#include "sqliteInt.h"
#include <string.h>
#include <tcl.h>

static struct Wrapped {
  sqlite3_pcache_methods2 pcache;
  sqlite3_mem_methods     mem;
  sqlite3_mutex_methods   mutex;

  int mem_init;                /* True if mem subsystem is initalized */
  int mem_fail;                /* True to fail mem subsystem inialization */
  int mutex_init;              /* True if mutex subsystem is initalized */
  int mutex_fail;              /* True to fail mutex subsystem inialization */
  int pcache_init;             /* True if pcache subsystem is initalized */
  int pcache_fail;             /* True to fail pcache subsystem inialization */
................................................................................
  return rc;
}
static void wrPCacheShutdown(void *pArg){
  wrapped.pcache.xShutdown(wrapped.pcache.pArg);
  wrapped.pcache_init = 0;
}

static sqlite3_pcache *wrPCacheCreate(int a, int b, int c){
  return wrapped.pcache.xCreate(a, b, c);
}  
static void wrPCacheCachesize(sqlite3_pcache *p, int n){
  wrapped.pcache.xCachesize(p, n);
}  
static int wrPCachePagecount(sqlite3_pcache *p){
  return wrapped.pcache.xPagecount(p);
}  
static sqlite3_pcache_page *wrPCacheFetch(sqlite3_pcache *p, unsigned a, int b){
  return wrapped.pcache.xFetch(p, a, b);
}  
static void wrPCacheUnpin(sqlite3_pcache *p, sqlite3_pcache_page *a, int b){
  wrapped.pcache.xUnpin(p, a, b);
}  
static void wrPCacheRekey(
  sqlite3_pcache *p, 
  sqlite3_pcache_page *a, 
  unsigned b, 
  unsigned c
){
  wrapped.pcache.xRekey(p, a, b, c);
}  
static void wrPCacheTruncate(sqlite3_pcache *p, unsigned a){
  wrapped.pcache.xTruncate(p, a);
}  
static void wrPCacheDestroy(sqlite3_pcache *p){
  wrapped.pcache.xDestroy(p);
................................................................................

static void installInitWrappers(void){
  sqlite3_mutex_methods mutexmethods = {
    wrMutexInit,  wrMutexEnd,   wrMutexAlloc,
    wrMutexFree,  wrMutexEnter, wrMutexTry,
    wrMutexLeave, wrMutexHeld,  wrMutexNotheld
  };
  sqlite3_pcache_methods2 pcachemethods = {
    0,
    wrPCacheInit,      wrPCacheShutdown,  wrPCacheCreate, 
    wrPCacheCachesize, wrPCachePagecount, wrPCacheFetch,
    wrPCacheUnpin,     wrPCacheRekey,     wrPCacheTruncate,  
    wrPCacheDestroy
  };
  sqlite3_mem_methods memmethods = {
................................................................................
  };

  memset(&wrapped, 0, sizeof(wrapped));

  sqlite3_shutdown();
  sqlite3_config(SQLITE_CONFIG_GETMUTEX, &wrapped.mutex);
  sqlite3_config(SQLITE_CONFIG_GETMALLOC, &wrapped.mem);
  sqlite3_config(SQLITE_CONFIG_GETPCACHE2, &wrapped.pcache);
  sqlite3_config(SQLITE_CONFIG_MUTEX, &mutexmethods);
  sqlite3_config(SQLITE_CONFIG_MALLOC, &memmethods);
  sqlite3_config(SQLITE_CONFIG_PCACHE2, &pcachemethods);
}

static int init_wrapper_install(
  ClientData clientData, /* Unused */
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int objc,              /* Number of arguments */
  Tcl_Obj *CONST objv[]  /* Command arguments */
................................................................................
    return TCL_ERROR;
  }

  memset(&wrapped, 0, sizeof(&wrapped));
  sqlite3_shutdown();
  sqlite3_config(SQLITE_CONFIG_MUTEX, &wrapped.mutex);
  sqlite3_config(SQLITE_CONFIG_MALLOC, &wrapped.mem);
  sqlite3_config(SQLITE_CONFIG_PCACHE2, &wrapped.pcache);
  return TCL_OK;
}

static int init_wrapper_clear(
  ClientData clientData, /* Unused */
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int objc,              /* Number of arguments */

/*
** Private implementation of a page cache.
*/
typedef struct testpcache testpcache;
struct testpcache {
  int szPage;               /* Size of each page.  Multiple of 8. */

  int bPurgeable;           /* True if the page cache is purgeable */
  int nFree;                /* Number of unused slots in a[] */
  int nPinned;              /* Number of pinned slots in a[] */
  unsigned iRand;           /* State of the PRNG */
  unsigned iMagic;          /* Magic number for sanity checking */
  struct testpcachePage {

    unsigned key;              /* The key for this page. 0 means unallocated */
    int isPinned;              /* True if the page is pinned */
    void *pData;               /* Data for this page */
  } a[TESTPCACHE_NPAGE];    /* All pages in the cache */
};

/*
** Get a random number using the PRNG in the given page cache.
*/
static unsigned testpcacheRandom(testpcache *p){
................................................................................
  return x;
}


/*
** Allocate a new page cache instance.
*/
static sqlite3_pcache *testpcacheCreate(int szPage, int bPurgeable){




  int nMem;
  char *x;
  testpcache *p;
  int i;
  assert( testpcacheGlobal.pDummy!=0 );
  szPage = (szPage+7)&~7;
  nMem = sizeof(testpcache) + TESTPCACHE_NPAGE*szPage;
  p = sqlite3_malloc( nMem );
  if( p==0 ) return 0;
  x = (char*)&p[1];
  p->szPage = szPage;

  p->nFree = TESTPCACHE_NPAGE;
  p->nPinned = 0;
  p->iRand = testpcacheGlobal.prngSeed;
  p->bPurgeable = bPurgeable;
  p->iMagic = TESTPCACHE_VALID;
  for(i=0; i<TESTPCACHE_NPAGE; i++, x += szPage){
    p->a[i].key = 0;
    p->a[i].isPinned = 0;
    p->a[i].pData = (void*)x;

  }
  testpcacheGlobal.nInstance++;
  return (sqlite3_pcache*)p;
}

/*
** Set the cache size
................................................................................
  assert( testpcacheGlobal.nInstance>0 );
  return TESTPCACHE_NPAGE - p->nFree;
}

/*
** Fetch a page.
*/
static void *testpcacheFetch(
  sqlite3_pcache *pCache,
  unsigned key,
  int createFlag
){
  testpcache *p = (testpcache*)pCache;
  int i, j;
  assert( p->iMagic==TESTPCACHE_VALID );
................................................................................
  for(i=0; i<TESTPCACHE_NPAGE; i++){
    if( p->a[i].key==key ){
      if( !p->a[i].isPinned ){
        p->nPinned++;
        assert( p->nPinned <= TESTPCACHE_NPAGE - p->nFree );
        p->a[i].isPinned = 1;
      }
      return p->a[i].pData;
    }
  }

  /* If createFlag is 0, never allocate a new page */
  if( createFlag==0 ){
    return 0;
  }
................................................................................
  */
  if( p->nFree>TESTPCACHE_RESERVE || (createFlag==2 && p->nFree>0) ){
    j = testpcacheRandom(p) % TESTPCACHE_NPAGE;
    for(i=0; i<TESTPCACHE_NPAGE; i++, j = (j+1)%TESTPCACHE_NPAGE){
      if( p->a[j].key==0 ){
        p->a[j].key = key;
        p->a[j].isPinned = 1;
        memset(p->a[j].pData, 0, p->szPage);

        p->nPinned++;
        p->nFree--;
        assert( p->nPinned <= TESTPCACHE_NPAGE - p->nFree );
        return p->a[j].pData;
      }
    }

    /* The prior loop always finds a freepage to allocate */
    assert( 0 );
  }

................................................................................
  ** recycle is selected at random from all unpinned pages.
  */
  j = testpcacheRandom(p) % TESTPCACHE_NPAGE;
  for(i=0; i<TESTPCACHE_NPAGE; i++, j = (j+1)%TESTPCACHE_NPAGE){
    if( p->a[j].key>0 && p->a[j].isPinned==0 ){
      p->a[j].key = key;
      p->a[j].isPinned = 1;
      memset(p->a[j].pData, 0, p->szPage);

      p->nPinned++;
      assert( p->nPinned <= TESTPCACHE_NPAGE - p->nFree );
      return p->a[j].pData;
    }
  }

  /* The previous loop always finds a page to recycle. */
  assert(0);
  return 0;
}

/*
** Unpin a page.
*/
static void testpcacheUnpin(
  sqlite3_pcache *pCache,
  void *pOldPage,
  int discard
){
  testpcache *p = (testpcache*)pCache;
  int i;
  assert( p->iMagic==TESTPCACHE_VALID );
  assert( testpcacheGlobal.pDummy!=0 );
  assert( testpcacheGlobal.nInstance>0 );
................................................................................
  if( p->bPurgeable
  && (100-testpcacheGlobal.discardChance) <= (testpcacheRandom(p)%100)
  ){
    discard = 1;
  }

  for(i=0; i<TESTPCACHE_NPAGE; i++){
    if( p->a[i].pData==pOldPage ){
      /* The pOldPage pointer always points to a pinned page */
      assert( p->a[i].isPinned );
      p->a[i].isPinned = 0;
      p->nPinned--;
      assert( p->nPinned>=0 );
      if( discard ){
        p->a[i].key = 0;
................................................................................


/*
** Rekey a single page.
*/
static void testpcacheRekey(
  sqlite3_pcache *pCache,
  void *pOldPage,
  unsigned oldKey,
  unsigned newKey
){
  testpcache *p = (testpcache*)pCache;
  int i;
  assert( p->iMagic==TESTPCACHE_VALID );
  assert( testpcacheGlobal.pDummy!=0 );
................................................................................
  }

  /* Find the page to be rekeyed and rekey it.
  */
  for(i=0; i<TESTPCACHE_NPAGE; i++){
    if( p->a[i].key==oldKey ){
      /* The oldKey and pOldPage parameters match */
      assert( p->a[i].pData==pOldPage );
      /* Page to be rekeyed must be pinned */
      assert( p->a[i].isPinned );
      p->a[i].key = newKey;
      return;
    }
  }

................................................................................
*/
void installTestPCache(
  int installFlag,            /* True to install.  False to uninstall. */
  unsigned discardChance,     /* 0-100.  Chance to discard on unpin */
  unsigned prngSeed,          /* Seed for the PRNG */
  unsigned highStress         /* Call xStress agressively */
){
  static const sqlite3_pcache_methods testPcache = {
    (void*)&testpcacheGlobal,
    testpcacheInit,
    testpcacheShutdown,
    testpcacheCreate,
    testpcacheCachesize,
    testpcachePagecount,
    testpcacheFetch,
    testpcacheUnpin,
    testpcacheRekey,
    testpcacheTruncate,
    testpcacheDestroy,
  };
  static sqlite3_pcache_methods defaultPcache;
  static int isInstalled = 0;

  assert( testpcacheGlobal.nInstance==0 );
  assert( testpcacheGlobal.pDummy==0 );
  assert( discardChance<=100 );
  testpcacheGlobal.discardChance = discardChance;
  testpcacheGlobal.prngSeed = prngSeed ^ (prngSeed<<16);
  testpcacheGlobal.highStress = highStress;
  if( installFlag!=isInstalled ){
    if( installFlag ){
      sqlite3_config(SQLITE_CONFIG_GETPCACHE, &defaultPcache);
      assert( defaultPcache.xCreate!=testpcacheCreate );
      sqlite3_config(SQLITE_CONFIG_PCACHE, &testPcache);
    }else{
      assert( defaultPcache.xCreate!=0 );
      sqlite3_config(SQLITE_CONFIG_PCACHE, &defaultPcache);
    }
    isInstalled = installFlag;
  }
}

/*
** Private implementation of a page cache.
*/
typedef struct testpcache testpcache;
struct testpcache {
  int szPage;               /* Size of each page.  Multiple of 8. */
  int szExtra;              /* Size of extra data that accompanies each page */
  int bPurgeable;           /* True if the page cache is purgeable */
  int nFree;                /* Number of unused slots in a[] */
  int nPinned;              /* Number of pinned slots in a[] */
  unsigned iRand;           /* State of the PRNG */
  unsigned iMagic;          /* Magic number for sanity checking */
  struct testpcachePage {
    sqlite3_pcache_page page;  /* Base class */
    unsigned key;              /* The key for this page. 0 means unallocated */
    int isPinned;              /* True if the page is pinned */

  } a[TESTPCACHE_NPAGE];    /* All pages in the cache */
};

/*
** Get a random number using the PRNG in the given page cache.
*/
static unsigned testpcacheRandom(testpcache *p){
................................................................................
  return x;
}


/*
** Allocate a new page cache instance.
*/
static sqlite3_pcache *testpcacheCreate(
  int szExtra, 
  int szPage, 
  int bPurgeable
){
  int nMem;
  char *x;
  testpcache *p;
  int i;
  assert( testpcacheGlobal.pDummy!=0 );
  szPage = (szPage+7)&~7;
  nMem = sizeof(testpcache) + TESTPCACHE_NPAGE*(szPage+szExtra);
  p = sqlite3_malloc( nMem );
  if( p==0 ) return 0;
  x = (char*)&p[1];
  p->szPage = szPage;
  p->szExtra = szExtra;
  p->nFree = TESTPCACHE_NPAGE;
  p->nPinned = 0;
  p->iRand = testpcacheGlobal.prngSeed;
  p->bPurgeable = bPurgeable;
  p->iMagic = TESTPCACHE_VALID;
  for(i=0; i<TESTPCACHE_NPAGE; i++, x += (szPage+szExtra)){
    p->a[i].key = 0;
    p->a[i].isPinned = 0;
    p->a[i].page.pBuf = (void*)x;
    p->a[i].page.pExtra = (void*)&x[szPage];
  }
  testpcacheGlobal.nInstance++;
  return (sqlite3_pcache*)p;
}

/*
** Set the cache size
................................................................................
  assert( testpcacheGlobal.nInstance>0 );
  return TESTPCACHE_NPAGE - p->nFree;
}

/*
** Fetch a page.
*/
static sqlite3_pcache_page *testpcacheFetch(
  sqlite3_pcache *pCache,
  unsigned key,
  int createFlag
){
  testpcache *p = (testpcache*)pCache;
  int i, j;
  assert( p->iMagic==TESTPCACHE_VALID );
................................................................................
  for(i=0; i<TESTPCACHE_NPAGE; i++){
    if( p->a[i].key==key ){
      if( !p->a[i].isPinned ){
        p->nPinned++;
        assert( p->nPinned <= TESTPCACHE_NPAGE - p->nFree );
        p->a[i].isPinned = 1;
      }
      return &p->a[i].page;
    }
  }

  /* If createFlag is 0, never allocate a new page */
  if( createFlag==0 ){
    return 0;
  }
................................................................................
  */
  if( p->nFree>TESTPCACHE_RESERVE || (createFlag==2 && p->nFree>0) ){
    j = testpcacheRandom(p) % TESTPCACHE_NPAGE;
    for(i=0; i<TESTPCACHE_NPAGE; i++, j = (j+1)%TESTPCACHE_NPAGE){
      if( p->a[j].key==0 ){
        p->a[j].key = key;
        p->a[j].isPinned = 1;
        memset(p->a[j].page.pBuf, 0, p->szPage);
        memset(p->a[j].page.pExtra, 0, p->szExtra);
        p->nPinned++;
        p->nFree--;
        assert( p->nPinned <= TESTPCACHE_NPAGE - p->nFree );
        return &p->a[j].page;
      }
    }

    /* The prior loop always finds a freepage to allocate */
    assert( 0 );
  }

................................................................................
  ** recycle is selected at random from all unpinned pages.
  */
  j = testpcacheRandom(p) % TESTPCACHE_NPAGE;
  for(i=0; i<TESTPCACHE_NPAGE; i++, j = (j+1)%TESTPCACHE_NPAGE){
    if( p->a[j].key>0 && p->a[j].isPinned==0 ){
      p->a[j].key = key;
      p->a[j].isPinned = 1;
      memset(p->a[j].page.pBuf, 0, p->szPage);
      memset(p->a[j].page.pExtra, 0, p->szExtra);
      p->nPinned++;
      assert( p->nPinned <= TESTPCACHE_NPAGE - p->nFree );
      return &p->a[j].page;
    }
  }

  /* The previous loop always finds a page to recycle. */
  assert(0);
  return 0;
}

/*
** Unpin a page.
*/
static void testpcacheUnpin(
  sqlite3_pcache *pCache,
  sqlite3_pcache_page *pOldPage,
  int discard
){
  testpcache *p = (testpcache*)pCache;
  int i;
  assert( p->iMagic==TESTPCACHE_VALID );
  assert( testpcacheGlobal.pDummy!=0 );
  assert( testpcacheGlobal.nInstance>0 );
................................................................................
  if( p->bPurgeable
  && (100-testpcacheGlobal.discardChance) <= (testpcacheRandom(p)%100)
  ){
    discard = 1;
  }

  for(i=0; i<TESTPCACHE_NPAGE; i++){
    if( &p->a[i].page==pOldPage ){
      /* The pOldPage pointer always points to a pinned page */
      assert( p->a[i].isPinned );
      p->a[i].isPinned = 0;
      p->nPinned--;
      assert( p->nPinned>=0 );
      if( discard ){
        p->a[i].key = 0;
................................................................................


/*
** Rekey a single page.
*/
static void testpcacheRekey(
  sqlite3_pcache *pCache,
  sqlite3_pcache_page *pOldPage,
  unsigned oldKey,
  unsigned newKey
){
  testpcache *p = (testpcache*)pCache;
  int i;
  assert( p->iMagic==TESTPCACHE_VALID );
  assert( testpcacheGlobal.pDummy!=0 );
................................................................................
  }

  /* Find the page to be rekeyed and rekey it.
  */
  for(i=0; i<TESTPCACHE_NPAGE; i++){
    if( p->a[i].key==oldKey ){
      /* The oldKey and pOldPage parameters match */
      assert( &p->a[i].page==pOldPage );
      /* Page to be rekeyed must be pinned */
      assert( p->a[i].isPinned );
      p->a[i].key = newKey;
      return;
    }
  }

................................................................................
*/
void installTestPCache(
  int installFlag,            /* True to install.  False to uninstall. */
  unsigned discardChance,     /* 0-100.  Chance to discard on unpin */
  unsigned prngSeed,          /* Seed for the PRNG */
  unsigned highStress         /* Call xStress agressively */
){
  static const sqlite3_pcache_methods2 testPcache = {
    (void*)&testpcacheGlobal,
    testpcacheInit,
    testpcacheShutdown,
    testpcacheCreate,
    testpcacheCachesize,
    testpcachePagecount,
    testpcacheFetch,
    testpcacheUnpin,
    testpcacheRekey,
    testpcacheTruncate,
    testpcacheDestroy,
  };
  static sqlite3_pcache_methods2 defaultPcache;
  static int isInstalled = 0;

  assert( testpcacheGlobal.nInstance==0 );
  assert( testpcacheGlobal.pDummy==0 );
  assert( discardChance<=100 );
  testpcacheGlobal.discardChance = discardChance;
  testpcacheGlobal.prngSeed = prngSeed ^ (prngSeed<<16);
  testpcacheGlobal.highStress = highStress;
  if( installFlag!=isInstalled ){
    if( installFlag ){
      sqlite3_config(SQLITE_CONFIG_GETPCACHE2, &defaultPcache);
      assert( defaultPcache.xCreate!=testpcacheCreate );
      sqlite3_config(SQLITE_CONFIG_PCACHE2, &testPcache);
    }else{
      assert( defaultPcache.xCreate!=0 );
      sqlite3_config(SQLITE_CONFIG_PCACHE2, &defaultPcache);
    }
    isInstalled = installFlag;
  }
}

  sqlite3_status SQLITE_STATUS_PAGECACHE_SIZE 1
  sqlite3_status SQLITE_STATUS_SCRATCH_USED 1
  sqlite3_status SQLITE_STATUS_SCRATCH_OVERFLOW 1
  sqlite3_status SQLITE_STATUS_SCRATCH_SIZE 1
  sqlite3_status SQLITE_STATUS_PARSER_STACK 1
}

set xtra_size 256

# Test 1:  Both PAGECACHE and SCRATCH are shut down.
#
db close
sqlite3_shutdown
sqlite3_config_lookaside 0 0
sqlite3_initialize

  sqlite3_status SQLITE_STATUS_PAGECACHE_SIZE 1
  sqlite3_status SQLITE_STATUS_SCRATCH_USED 1
  sqlite3_status SQLITE_STATUS_SCRATCH_OVERFLOW 1
  sqlite3_status SQLITE_STATUS_SCRATCH_SIZE 1
  sqlite3_status SQLITE_STATUS_PARSER_STACK 1
}

set xtra_size 272

# Test 1:  Both PAGECACHE and SCRATCH are shut down.
#
db close
sqlite3_shutdown
sqlite3_config_lookaside 0 0
sqlite3_initialize