mem2.c

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/*
** 2007 August 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    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 contains the C functions that implement a memory
** allocation subsystem for use by SQLite.  
**
** $Id: mem2.c,v 1.18 2007/11/29 18:36:49 drh Exp $
*/

/*
** This version of the memory allocator is used only if the
** SQLITE_MEMDEBUG macro is defined and SQLITE_OMIT_MEMORY_ALLOCATION
** is not defined.
*/
#if defined(SQLITE_MEMDEBUG)

/*
** We will eventually construct multiple memory allocation subsystems
** suitable for use in various contexts:
**
**    *  Normal multi-threaded builds
**    *  Normal single-threaded builds
**    *  Debugging builds
**
** This version is suitable for use in debugging builds.
**
** Features:
**
**    * Every allocate has guards at both ends.
**    * New allocations are initialized with randomness
**    * Allocations are overwritten with randomness when freed
**    * Optional logs of malloc activity generated
**    * Summary of outstanding allocations with backtraces to the
**      point of allocation.
**    * The ability to simulate memory allocation failure
*/
#include "sqliteInt.h"
#include <stdio.h>

/*
** The backtrace functionality is only available with GLIBC
*/
#ifdef __GLIBC__
  extern int backtrace(void**,int);
  extern void backtrace_symbols_fd(void*const*,int,int);
#else
# define backtrace(A,B) 0
# define backtrace_symbols_fd(A,B,C)
#endif

/*
** Each memory allocation looks like this:
**
**  ------------------------------------------------------------------------
**  | Title |  backtrace pointers |  MemBlockHdr |  allocation |  EndGuard |
**  ------------------------------------------------------------------------
**
** The application code sees only a pointer to the allocation.  We have
** to back up from the allocation pointer to find the MemBlockHdr.  The
** MemBlockHdr tells us the size of the allocation and the number of
** backtrace pointers.  There is also a guard word at the end of the
** MemBlockHdr.
*/
struct MemBlockHdr {
  struct MemBlockHdr *pNext, *pPrev;  /* Linked list of all unfreed memory */
  int iSize;                          /* Size of this allocation */
  char nBacktrace;                    /* Number of backtraces on this alloc */
  char nBacktraceSlots;               /* Available backtrace slots */
  short nTitle;                       /* Bytes of title; includes '\0' */
  int iForeGuard;                     /* Guard word for sanity */
};

/*
** Guard words
*/
#define FOREGUARD 0x80F5E153
#define REARGUARD 0xE4676B53

/*
** Number of malloc size increments to track.
*/
#define NCSIZE  1000

/*
** All of the static variables used by this module are collected
** into a single structure named "mem".  This is to keep the
** static variables organized and to reduce namespace pollution
** when this module is combined with other in the amalgamation.
*/
static struct {
  /*
  ** The alarm callback and its arguments.  The mem.mutex lock will
  ** be held while the callback is running.  Recursive calls into
  ** the memory subsystem are allowed, but no new callbacks will be
  ** issued.  The alarmBusy variable is set to prevent recursive
  ** callbacks.
  */
  sqlite3_int64 alarmThreshold;
  void (*alarmCallback)(void*, sqlite3_int64, int);
  void *alarmArg;
  int alarmBusy;
  
  /*
  ** Mutex to control access to the memory allocation subsystem.
  */
  sqlite3_mutex *mutex;
  
  /*
  ** Current allocation and high-water mark.
  */
  sqlite3_int64 nowUsed;
  sqlite3_int64 mxUsed;
  
  /*
  ** Head and tail of a linked list of all outstanding allocations
  */
  struct MemBlockHdr *pFirst;
  struct MemBlockHdr *pLast;
  
  /*
  ** The number of levels of backtrace to save in new allocations.
  */
  int nBacktrace;

  /*
  ** Title text to insert in front of each block
  */
  int nTitle;        /* Bytes of zTitle to save.  Includes '\0' and padding */
  char zTitle[100];  /* The title text */

  /*
  ** These values are used to simulate malloc failures.  When
  ** iFail is 1, simulate a malloc failures and reset the value
  ** to iReset.
  */
  int iFail;    /* Decrement and fail malloc when this is 1 */
  int iReset;   /* When malloc fails set iiFail to this value */
  int iFailCnt;         /* Number of failures */
  int iBenignFailCnt;   /* Number of benign failures */
  int iNextIsBenign;    /* True if the next call to malloc may fail benignly */
  int iIsBenign;        /* All malloc calls may fail benignly */

  /* 
  ** sqlite3MallocDisallow() increments the following counter.
  ** sqlite3MallocAllow() decrements it.
  */
  int disallow; /* Do not allow memory allocation */

  /*
  ** Gather statistics on the sizes of memory allocations.
  ** sizeCnt[i] is the number of allocation attempts of i*8
  ** bytes.  i==NCSIZE is the number of allocation attempts for
  ** sizes more than NCSIZE*8 bytes.
  */
  int sizeCnt[NCSIZE];

} mem;


/*
** Enter the mutex mem.mutex. Allocate it if it is not already allocated.
*/
static void enterMem(void){
  if( mem.mutex==0 ){
    mem.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MEM);
  }
  sqlite3_mutex_enter(mem.mutex);
}

/*
** Return the amount of memory currently checked out.
*/
sqlite3_int64 sqlite3_memory_used(void){
  sqlite3_int64 n;
  enterMem();
  n = mem.nowUsed;
  sqlite3_mutex_leave(mem.mutex);  
  return n;
}

/*
** Return the maximum amount of memory that has ever been
** checked out since either the beginning of this process
** or since the most recent reset.
*/
sqlite3_int64 sqlite3_memory_highwater(int resetFlag){
  sqlite3_int64 n;
  enterMem();
  n = mem.mxUsed;
  if( resetFlag ){
    mem.mxUsed = mem.nowUsed;
  }
  sqlite3_mutex_leave(mem.mutex);  
  return n;
}

/*
** Change the alarm callback
*/
int sqlite3_memory_alarm(
  void(*xCallback)(void *pArg, sqlite3_int64 used, int N),
  void *pArg,
  sqlite3_int64 iThreshold
){
  enterMem();
  mem.alarmCallback = xCallback;
  mem.alarmArg = pArg;
  mem.alarmThreshold = iThreshold;
  sqlite3_mutex_leave(mem.mutex);
  return SQLITE_OK;
}

/*
** Trigger the alarm 
*/
static void sqlite3MemsysAlarm(int nByte){
  void (*xCallback)(void*,sqlite3_int64,int);
  sqlite3_int64 nowUsed;
  void *pArg;
  if( mem.alarmCallback==0 || mem.alarmBusy  ) return;
  mem.alarmBusy = 1;
  xCallback = mem.alarmCallback;
  nowUsed = mem.nowUsed;
  pArg = mem.alarmArg;
  sqlite3_mutex_leave(mem.mutex);
  xCallback(pArg, nowUsed, nByte);
  sqlite3_mutex_enter(mem.mutex);
  mem.alarmBusy = 0;
}

/*
** Given an allocation, find the MemBlockHdr for that allocation.
**
** This routine checks the guards at either end of the allocation and
** if they are incorrect it asserts.
*/
static struct MemBlockHdr *sqlite3MemsysGetHeader(void *pAllocation){
  struct MemBlockHdr *p;
  int *pInt;

  p = (struct MemBlockHdr*)pAllocation;
  p--;
  assert( p->iForeGuard==FOREGUARD );
  assert( (p->iSize & 3)==0 );
  pInt = (int*)pAllocation;
  assert( pInt[p->iSize/sizeof(int)]==REARGUARD );
  return p;
}

/*
** This routine is called once the first time a simulated memory
** failure occurs.  The sole purpose of this routine is to provide
** a convenient place to set a debugger breakpoint when debugging
** errors related to malloc() failures.
*/
static void sqlite3MemsysFailed(void){
  mem.iFailCnt = 0;
  mem.iBenignFailCnt = 0;
}

/*
** Allocate nByte bytes of memory.
*/
void *sqlite3_malloc(int nByte){
  struct MemBlockHdr *pHdr;
  void **pBt;
  char *z;
  int *pInt;
  void *p = 0;
  int totalSize;

  if( nByte>0 ){
    enterMem();
    assert( mem.disallow==0 );
    if( mem.alarmCallback!=0 && mem.nowUsed+nByte>=mem.alarmThreshold ){
      sqlite3MemsysAlarm(nByte);
    }
    nByte = (nByte+3)&~3;
    if( nByte/8>NCSIZE-1 ){