SQLite

**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** Memory allocation functions used throughout sqlite.
**
** $Id: malloc.c,v 1.56 2009/02/17 18:37:29 drh Exp $
*/
#include "sqliteInt.h"
#include <stdarg.h>

/*
** This routine runs when the memory allocator sees that the
** total memory allocation is about to exceed the soft heap

      mem0.aScratchFree[mem0.nScratchFree++] = i;
      sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_USED, -1);
      sqlite3_mutex_leave(mem0.mutex);
    }
  }
}

/*
** Allocate memory to be used by the page cache.  Make use of the
** memory buffer provided by SQLITE_CONFIG_PAGECACHE if there is one
** and that memory is of the right size and is not completely
** consumed.  Otherwise, failover to sqlite3Malloc().
*/
#if 0
void *sqlite3PageMalloc(int n){
  void *p;
  assert( n>0 );
  assert( (n & (n-1))==0 );
  assert( n>=512 && n<=32768 );

  if( sqlite3GlobalConfig.szPage<n ){
    goto page_overflow;
  }else{  
    sqlite3_mutex_enter(mem0.mutex);
    if( mem0.nPageFree==0 ){
      sqlite3_mutex_leave(mem0.mutex);
      goto page_overflow;
    }else{
      int i;
      i = mem0.aPageFree[--mem0.nPageFree];
      sqlite3_mutex_leave(mem0.mutex);
      i *= sqlite3GlobalConfig.szPage;
      sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, n);
      sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, 1);
      p = (void*)&((char*)sqlite3GlobalConfig.pPage)[i];
    }
  }
  return p;

page_overflow:
  if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, n);
    n = mallocWithAlarm(n, &p);
    if( p ) sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, n);
    sqlite3_mutex_leave(mem0.mutex);
  }else{
    p = sqlite3GlobalConfig.m.xMalloc(n);
  }
  return p;    
}
void sqlite3PageFree(void *p){
  if( p ){
    if( sqlite3GlobalConfig.pPage==0
           || p<sqlite3GlobalConfig.pPage
           || p>=(void*)mem0.aPageFree ){
      /* In this case, the page allocation was obtained from a regular 
      ** call to sqlite3_mem_methods.xMalloc() (a page-cache-memory 
      ** "overflow"). Free the block with sqlite3_mem_methods.xFree().
      */
      if( sqlite3GlobalConfig.bMemstat ){
        int iSize = sqlite3MallocSize(p);
        sqlite3_mutex_enter(mem0.mutex);
        sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_OVERFLOW, -iSize);
        sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -iSize);
        sqlite3GlobalConfig.m.xFree(p);
        sqlite3_mutex_leave(mem0.mutex);
      }else{
        sqlite3GlobalConfig.m.xFree(p);
      }
    }else{
      /* The page allocation was allocated from the sqlite3GlobalConfig.pPage
      ** buffer. In this case all that is add the index of the page in
      ** the sqlite3GlobalConfig.pPage array to the set of free indexes stored
      ** in the mem0.aPageFree[] array.
      */
      int i;
      i = (u8 *)p - (u8 *)sqlite3GlobalConfig.pPage;
      i /= sqlite3GlobalConfig.szPage;
      assert( i>=0 && i<sqlite3GlobalConfig.nPage );
      sqlite3_mutex_enter(mem0.mutex);
      assert( mem0.nPageFree<sqlite3GlobalConfig.nPage );
      mem0.aPageFree[mem0.nPageFree++] = i;
      sqlite3StatusAdd(SQLITE_STATUS_PAGECACHE_USED, -1);
      sqlite3_mutex_leave(mem0.mutex);
#if !defined(NDEBUG) && 0
      /* Assert that a duplicate was not just inserted into aPageFree[]. */
      for(i=0; i<mem0.nPageFree-1; i++){
        assert( mem0.aPageFree[i]!=mem0.aPageFree[mem0.nPageFree-1] );
      }
#endif
    }
  }
}
#endif

/*
** TRUE if p is a lookaside memory allocation from db
*/
#ifndef SQLITE_OMIT_LOOKASIDE
static int isLookaside(sqlite3 *db, void *p){
  return db && p && p>=db->lookaside.pStart && p<db->lookaside.pEnd;
}