engine/sqlite/src/mem1.cpp
author Sebastian Brannstrom <sebastianb@symbian.org>
Fri, 09 Jul 2010 23:58:47 +0100
branch3rded
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permissions -rw-r--r--
Started port to 3rd edition
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/*
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** 2007 August 14
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**
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** The author disclaims copyright to this source code.  In place of
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** a legal notice, here is a blessing:
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**
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**    May you do good and not evil.
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**    May you find forgiveness for yourself and forgive others.
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**    May you share freely, never taking more than you give.
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**
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*************************************************************************
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** This file contains the C functions that implement a memory
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** allocation subsystem for use by SQLite.  
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**
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** $Id: mem1.cpp 1282 2008-11-13 09:31:33Z LarsPson $
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*/
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/*
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** This version of the memory allocator is the default.  It is
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** used when no other memory allocator is specified using compile-time
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** macros.
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*/
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#if !defined(SQLITE_MEMDEBUG) && !defined(SQLITE_MEMORY_SIZE) \
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     && !defined(SQLITE_MMAP_HEAP_SIZE)
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/*
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** We will eventually construct multiple memory allocation subsystems
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** suitable for use in various contexts:
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**
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**    *  Normal multi-threaded builds
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**    *  Normal single-threaded builds
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**    *  Debugging builds
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**
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** This initial version is suitable for use in normal multi-threaded
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** builds.  We envision that alternative versions will be stored in
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** separate source files.  #ifdefs will be used to select the code from
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** one of the various memN.c source files for use in any given build.
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*/
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#include "sqliteInt.h"
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/*
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** All of the static variables used by this module are collected
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** into a single structure named "mem".  This is to keep the
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** static variables organized and to reduce namespace pollution
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** when this module is combined with other in the amalgamation.
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*/
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static struct {
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  /*
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  ** The alarm callback and its arguments.  The mem.mutex lock will
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  ** be held while the callback is running.  Recursive calls into
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  ** the memory subsystem are allowed, but no new callbacks will be
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  ** issued.  The alarmBusy variable is set to prevent recursive
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  ** callbacks.
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  */
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  sqlite3_int64 alarmThreshold;
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  void (*alarmCallback)(void*, sqlite3_int64,int);
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  void *alarmArg;
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  int alarmBusy;
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  /*
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  ** Mutex to control access to the memory allocation subsystem.
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  */
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  sqlite3_mutex *mutex;
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  /*
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  ** Current allocation and high-water mark.
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  */
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  sqlite3_int64 nowUsed;
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  sqlite3_int64 mxUsed;
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} mem;
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/*
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** Enter the mutex mem.mutex. Allocate it if it is not already allocated.
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*/
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static void enterMem(void){
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  if( mem.mutex==0 ){
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    mem.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MEM);
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  }
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  sqlite3_mutex_enter(mem.mutex);
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}
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/*
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** Return the amount of memory currently checked out.
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*/
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EXPORT_C sqlite3_int64 sqlite3_memory_used(void){
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  sqlite3_int64 n;
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  enterMem();
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  n = mem.nowUsed;
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  sqlite3_mutex_leave(mem.mutex);  
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  return n;
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}
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/*
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** Return the maximum amount of memory that has ever been
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** checked out since either the beginning of this process
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** or since the most recent reset.
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*/
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EXPORT_C sqlite3_int64 sqlite3_memory_highwater(int resetFlag){
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  sqlite3_int64 n;
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  enterMem();
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  n = mem.mxUsed;
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  if( resetFlag ){
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    mem.mxUsed = mem.nowUsed;
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  }
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  sqlite3_mutex_leave(mem.mutex);  
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  return n;
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}
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/*
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** Change the alarm callback
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*/
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EXPORT_C int sqlite3_memory_alarm(
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  void(*xCallback)(void *pArg, sqlite3_int64 used,int N),
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  void *pArg,
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  sqlite3_int64 iThreshold
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){
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  enterMem();
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  mem.alarmCallback = xCallback;
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  mem.alarmArg = pArg;
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  mem.alarmThreshold = iThreshold;
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  sqlite3_mutex_leave(mem.mutex);
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  return SQLITE_OK;
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}
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/*
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** Trigger the alarm 
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*/
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static void sqlite3MemsysAlarm(int nByte){
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  void (*xCallback)(void*,sqlite3_int64,int);
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  sqlite3_int64 nowUsed;
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  void *pArg;
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  if( mem.alarmCallback==0 || mem.alarmBusy  ) return;
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  mem.alarmBusy = 1;
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  xCallback = mem.alarmCallback;
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  nowUsed = mem.nowUsed;
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  pArg = mem.alarmArg;
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  sqlite3_mutex_leave(mem.mutex);
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  xCallback(pArg, nowUsed, nByte);
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  sqlite3_mutex_enter(mem.mutex);
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  mem.alarmBusy = 0;
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}
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/*
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** Allocate nBytes of memory
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*/
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EXPORT_C void *sqlite3_malloc(int nBytes){
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  sqlite3_int64 *p = 0;
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  if( nBytes>0 ){
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    enterMem();
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    if( mem.alarmCallback!=0 && mem.nowUsed+nBytes>=mem.alarmThreshold ){
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      sqlite3MemsysAlarm(nBytes);
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    }
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	p = (sqlite3_int64*)malloc(nBytes+8);
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    if( p==0 ){
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      sqlite3MemsysAlarm(nBytes);
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	  p = (sqlite3_int64*)malloc(nBytes+8);
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    }
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    if( p ){
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      p[0] = nBytes;
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      p++;
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      mem.nowUsed += nBytes;
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      if( mem.nowUsed>mem.mxUsed ){
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        mem.mxUsed = mem.nowUsed;
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      }
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    }
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    sqlite3_mutex_leave(mem.mutex);
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  }
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  return (void*)p; 
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}
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/*
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** Free memory.
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*/
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EXPORT_C void sqlite3_free(void *pPrior){
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  sqlite3_int64 *p;
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  int nByte;
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  if( pPrior==0 ){
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    return;
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  }
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  assert( mem.mutex!=0 );
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  p = (sqlite3_int64*)pPrior;
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  p--;
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  nByte = (int)*p;
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  sqlite3_mutex_enter(mem.mutex);
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  mem.nowUsed -= nByte;
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  free(p);
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  sqlite3_mutex_leave(mem.mutex);  
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}
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/*
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** Change the size of an existing memory allocation
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*/
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EXPORT_C void *sqlite3_realloc(void *pPrior, int nBytes){
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  int nOld;
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  sqlite3_int64 *p;
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  if( pPrior==0 ){
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    return sqlite3_malloc(nBytes);
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  }
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  if( nBytes<=0 ){
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    sqlite3_free(pPrior);
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    return 0;
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  }
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  p = (sqlite3_int64*)pPrior;
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  p--;
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  nOld = (int)p[0];
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  assert( mem.mutex!=0 );
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  sqlite3_mutex_enter(mem.mutex);
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  if( mem.nowUsed+nBytes-nOld>=mem.alarmThreshold ){
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    sqlite3MemsysAlarm(nBytes-nOld);
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  }
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  p = (sqlite3_int64*)realloc(p, nBytes+8);
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  if( p==0 ){
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    sqlite3MemsysAlarm(nBytes);
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	p = (sqlite3_int64*)pPrior;
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    p--;
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	p = (sqlite3_int64*)realloc(p, nBytes+8);
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  }
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  if( p ){
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    p[0] = nBytes;
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    p++;
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    mem.nowUsed += nBytes-nOld;
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    if( mem.nowUsed>mem.mxUsed ){
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      mem.mxUsed = mem.nowUsed;
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    }
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  }
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  sqlite3_mutex_leave(mem.mutex);
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  return (void*)p;
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}
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#endif /* !SQLITE_MEMDEBUG && !SQLITE_OMIT_MEMORY_ALLOCATION */