src/malloc.c

   1 /*
   2 ** 2001 September 15
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 **
  13 ** Memory allocation functions used throughout sqlite.
  14 */
  15 #include "sqliteInt.h"
  16 #include <stdarg.h>
  17
  18 /*
  19 ** Attempt to release up to n bytes of non-essential memory currently
  20 ** held by SQLite. An example of non-essential memory is memory used to
  21 ** cache database pages that are not currently in use.
  22 */
  23 int sqlite3_release_memory(int n){
  24 #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
  25   return sqlite3PcacheReleaseMemory(n);
  26 #else
  27   /* IMPLEMENTATION-OF: R-34391-24921 The sqlite3_release_memory() routine
  28   ** is a no-op returning zero if SQLite is not compiled with
  29   ** SQLITE_ENABLE_MEMORY_MANAGEMENT. */
  30   UNUSED_PARAMETER(n);
  31   return 0;
  32 #endif
  33 }
  34
  35 /*
  36 ** An instance of the following object records the location of
  37 ** each unused scratch buffer.
  38 */
  39 typedef struct ScratchFreeslot {
  40   struct ScratchFreeslot *pNext;   /* Next unused scratch buffer */
  41 } ScratchFreeslot;
  42
  43 /*
  44 ** State information local to the memory allocation subsystem.
  45 */
  46 static SQLITE_WSD struct Mem0Global {
  47   sqlite3_mutex *mutex;         /* Mutex to serialize access */
  48
  49   /*
  50   ** The alarm callback and its arguments.  The mem0.mutex lock will
  51   ** be held while the callback is running.  Recursive calls into
  52   ** the memory subsystem are allowed, but no new callbacks will be
  53   ** issued.
  54   */
  55   sqlite3_int64 alarmThreshold;
  56   void (*alarmCallback)(void*, sqlite3_int64,int);
  57   void *alarmArg;
  58
  59   /*
  60   ** Pointers to the end of sqlite3GlobalConfig.pScratch memory
  61   ** (so that a range test can be used to determine if an allocation
  62   ** being freed came from pScratch) and a pointer to the list of
  63   ** unused scratch allocations.
  64   */
  65   void *pScratchEnd;
  66   ScratchFreeslot *pScratchFree;
  67   u32 nScratchFree;
  68
  69   /*
  70   ** True if heap is nearly "full" where "full" is defined by the
  71   ** sqlite3_soft_heap_limit() setting.
  72   */
  73   int nearlyFull;
  74 } mem0 = { 0, 0, 0, 0, 0, 0, 0, 0 };
  75
  76 #define mem0 GLOBAL(struct Mem0Global, mem0)
  77
  78 /*
  79 ** This routine runs when the memory allocator sees that the
  80 ** total memory allocation is about to exceed the soft heap
  81 ** limit.
  82 */
  83 static void softHeapLimitEnforcer(
  84   void *NotUsed,
  85   sqlite3_int64 NotUsed2,
  86   int allocSize
  87 ){
  88   UNUSED_PARAMETER2(NotUsed, NotUsed2);
  89   sqlite3_release_memory(allocSize);
  90 }
  91
  92 /*
  93 ** Change the alarm callback
  94 */
  95 static int sqlite3MemoryAlarm(
  96   void(*xCallback)(void *pArg, sqlite3_int64 used,int N),
  97   void *pArg,
  98   sqlite3_int64 iThreshold
  99 ){
 100   int nUsed;
 101   sqlite3_mutex_enter(mem0.mutex);
 102   mem0.alarmCallback = xCallback;
 103   mem0.alarmArg = pArg;
 104   mem0.alarmThreshold = iThreshold;
 105   nUsed = sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED);
 106   mem0.nearlyFull = (iThreshold>0 && iThreshold<=nUsed);
 107   sqlite3_mutex_leave(mem0.mutex);
 108   return SQLITE_OK;
 109 }
 110
 111 #ifndef SQLITE_OMIT_DEPRECATED
 112 /*
 113 ** Deprecated external interface.  Internal/core SQLite code
 114 ** should call sqlite3MemoryAlarm.
 115 */
 116 int sqlite3_memory_alarm(
 117   void(*xCallback)(void *pArg, sqlite3_int64 used,int N),
 118   void *pArg,
 119   sqlite3_int64 iThreshold
 120 ){
 121   return sqlite3MemoryAlarm(xCallback, pArg, iThreshold);
 122 }
 123 #endif
 124
 125 /*
 126 ** Set the soft heap-size limit for the library. Passing a zero or
 127 ** negative value indicates no limit.
 128 */
 129 sqlite3_int64 sqlite3_soft_heap_limit64(sqlite3_int64 n){
 130   sqlite3_int64 priorLimit;
 131   sqlite3_int64 excess;
 132 #ifndef SQLITE_OMIT_AUTOINIT
 133   int rc = sqlite3_initialize();
 134   if( rc ) return -1;
 135 #endif
 136   sqlite3_mutex_enter(mem0.mutex);
 137   priorLimit = mem0.alarmThreshold;
 138   sqlite3_mutex_leave(mem0.mutex);
 139   if( n<0 ) return priorLimit;
 140   if( n>0 ){
 141     sqlite3MemoryAlarm(softHeapLimitEnforcer, 0, n);
 142   }else{
 143     sqlite3MemoryAlarm(0, 0, 0);
 144   }
 145   excess = sqlite3_memory_used() - n;
 146   if( excess>0 ) sqlite3_release_memory((int)(excess & 0x7fffffff));
 147   return priorLimit;
 148 }
 149 void sqlite3_soft_heap_limit(int n){
 150   if( n<0 ) n = 0;
 151   sqlite3_soft_heap_limit64(n);
 152 }
 153
 154 /*
 155 ** Initialize the memory allocation subsystem.
 156 */
 157 int sqlite3MallocInit(void){
 158   if( sqlite3GlobalConfig.m.xMalloc==0 ){
 159     sqlite3MemSetDefault();
 160   }
 161   memset(&mem0, 0, sizeof(mem0));
 162   if( sqlite3GlobalConfig.bCoreMutex ){
 163     mem0.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
 164   }
 165   if( sqlite3GlobalConfig.pScratch && sqlite3GlobalConfig.szScratch>=100
 166       && sqlite3GlobalConfig.nScratch>0 ){
 167     int i, n, sz;
 168     ScratchFreeslot *pSlot;
 169     sz = ROUNDDOWN8(sqlite3GlobalConfig.szScratch);
 170     sqlite3GlobalConfig.szScratch = sz;
 171     pSlot = (ScratchFreeslot*)sqlite3GlobalConfig.pScratch;
 172     n = sqlite3GlobalConfig.nScratch;
 173     mem0.pScratchFree = pSlot;
 174     mem0.nScratchFree = n;
 175     for(i=0; i<n-1; i++){
 176       pSlot->pNext = (ScratchFreeslot*)(sz+(char*)pSlot);
 177       pSlot = pSlot->pNext;
 178     }
 179     pSlot->pNext = 0;
 180     mem0.pScratchEnd = (void*)&pSlot[1];
 181   }else{
 182     mem0.pScratchEnd = 0;
 183     sqlite3GlobalConfig.pScratch = 0;
 184     sqlite3GlobalConfig.szScratch = 0;
 185     sqlite3GlobalConfig.nScratch = 0;
 186   }
 187   if( sqlite3GlobalConfig.pPage==0 || sqlite3GlobalConfig.szPage<512
 188       || sqlite3GlobalConfig.nPage<1 ){
 189     sqlite3GlobalConfig.pPage = 0;
 190     sqlite3GlobalConfig.szPage = 0;
 191     sqlite3GlobalConfig.nPage = 0;
 192   }
 193   return sqlite3GlobalConfig.m.xInit(sqlite3GlobalConfig.m.pAppData);
 194 }
 195
 196 /*
 197 ** Return true if the heap is currently under memory pressure - in other
 198 ** words if the amount of heap used is close to the limit set by
 199 ** sqlite3_soft_heap_limit().
 200 */
 201 int sqlite3HeapNearlyFull(void){
 202   return mem0.nearlyFull;
 203 }
 204
 205 /*
 206 ** Deinitialize the memory allocation subsystem.
 207 */
 208 void sqlite3MallocEnd(void){
 209   if( sqlite3GlobalConfig.m.xShutdown ){
 210     sqlite3GlobalConfig.m.xShutdown(sqlite3GlobalConfig.m.pAppData);
 211   }
 212   memset(&mem0, 0, sizeof(mem0));
 213 }
 214
 215 /*
 216 ** Return the amount of memory currently checked out.
 217 */
 218 sqlite3_int64 sqlite3_memory_used(void){
 219   int n, mx;
 220   sqlite3_int64 res;
 221   sqlite3_status(SQLITE_STATUS_MEMORY_USED, &n, &mx, 0);
 222   res = (sqlite3_int64)n;  /* Work around bug in Borland C. Ticket #3216 */
 223   return res;
 224 }
 225
 226 /*
 227 ** Return the maximum amount of memory that has ever been
 228 ** checked out since either the beginning of this process
 229 ** or since the most recent reset.
 230 */
 231 sqlite3_int64 sqlite3_memory_highwater(int resetFlag){
 232   int n, mx;
 233   sqlite3_int64 res;
 234   sqlite3_status(SQLITE_STATUS_MEMORY_USED, &n, &mx, resetFlag);
 235   res = (sqlite3_int64)mx;  /* Work around bug in Borland C. Ticket #3216 */
 236   return res;
 237 }
 238
 239 /*
 240 ** Trigger the alarm
 241 */
 242 static void sqlite3MallocAlarm(int nByte){
 243   void (*xCallback)(void*,sqlite3_int64,int);
 244   sqlite3_int64 nowUsed;
 245   void *pArg;
 246   if( mem0.alarmCallback==0 ) return;
 247   xCallback = mem0.alarmCallback;
 248   nowUsed = sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED);
 249   pArg = mem0.alarmArg;
 250   mem0.alarmCallback = 0;
 251   sqlite3_mutex_leave(mem0.mutex);
 252   xCallback(pArg, nowUsed, nByte);
 253   sqlite3_mutex_enter(mem0.mutex);
 254   mem0.alarmCallback = xCallback;
 255   mem0.alarmArg = pArg;
 256 }
 257
 258 /*
 259 ** Do a memory allocation with statistics and alarms.  Assume the
 260 ** lock is already held.
 261 */
 262 static int mallocWithAlarm(int n, void **pp){
 263   int nFull;
 264   void *p;
 265   assert( sqlite3_mutex_held(mem0.mutex) );
 266   nFull = sqlite3GlobalConfig.m.xRoundup(n);
 267   sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, n);
 268   if( mem0.alarmCallback!=0 ){
 269     int nUsed = sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED);
 270     if( nUsed >= mem0.alarmThreshold - nFull ){
 271       mem0.nearlyFull = 1;
 272       sqlite3MallocAlarm(nFull);
 273     }else{
 274       mem0.nearlyFull = 0;
 275     }
 276   }
 277   p = sqlite3GlobalConfig.m.xMalloc(nFull);
 278 #ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
 279   if( p==0 && mem0.alarmCallback ){
 280     sqlite3MallocAlarm(nFull);
 281     p = sqlite3GlobalConfig.m.xMalloc(nFull);
 282   }
 283 #endif
 284   if( p ){
 285     nFull = sqlite3MallocSize(p);
 286     sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, nFull);
 287     sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, 1);
 288   }
 289   *pp = p;
 290   return nFull;
 291 }
 292
 293 /*
 294 ** Allocate memory.  This routine is like sqlite3_malloc() except that it
 295 ** assumes the memory subsystem has already been initialized.
 296 */
 297 void *sqlite3Malloc(int n){
 298   void *p;
 299   if( n<=0               /* IMP: R-65312-04917 */
 300    || n>=0x7fffff00
 301   ){
 302     /* A memory allocation of a number of bytes which is near the maximum
 303     ** signed integer value might cause an integer overflow inside of the
 304     ** xMalloc().  Hence we limit the maximum size to 0x7fffff00, giving
 305     ** 255 bytes of overhead.  SQLite itself will never use anything near
 306     ** this amount.  The only way to reach the limit is with sqlite3_malloc() */
 307     p = 0;
 308   }else if( sqlite3GlobalConfig.bMemstat ){
 309     sqlite3_mutex_enter(mem0.mutex);
 310     mallocWithAlarm(n, &p);
 311     sqlite3_mutex_leave(mem0.mutex);
 312   }else{
 313     p = sqlite3GlobalConfig.m.xMalloc(n);
 314   }
 315   assert( EIGHT_BYTE_ALIGNMENT(p) );  /* IMP: R-04675-44850 */
 316   return p;
 317 }
 318
 319 /*
 320 ** This version of the memory allocation is for use by the application.
 321 ** First make sure the memory subsystem is initialized, then do the
 322 ** allocation.
 323 */
 324 void *sqlite3_malloc(int n){
 325 #ifndef SQLITE_OMIT_AUTOINIT
 326   if( sqlite3_initialize() ) return 0;
 327 #endif
 328   return sqlite3Malloc(n);
 329 }
 330
 331 /*
 332 ** Each thread may only have a single outstanding allocation from
 333 ** xScratchMalloc().  We verify this constraint in the single-threaded
 334 ** case by setting scratchAllocOut to 1 when an allocation
 335 ** is outstanding clearing it when the allocation is freed.
 336 */
 337 #if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
 338 static int scratchAllocOut = 0;
 339 #endif
 340
 341
 342 /*
 343 ** Allocate memory that is to be used and released right away.
 344 ** This routine is similar to alloca() in that it is not intended
 345 ** for situations where the memory might be held long-term.  This
 346 ** routine is intended to get memory to old large transient data
 347 ** structures that would not normally fit on the stack of an
 348 ** embedded processor.
 349 */
 350 void *sqlite3ScratchMalloc(int n){
 351   void *p;
 352   assert( n>0 );
 353
 354   sqlite3_mutex_enter(mem0.mutex);
 355   if( mem0.nScratchFree && sqlite3GlobalConfig.szScratch>=n ){
 356     p = mem0.pScratchFree;
 357     mem0.pScratchFree = mem0.pScratchFree->pNext;
 358     mem0.nScratchFree--;
 359     sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_USED, 1);
 360     sqlite3StatusSet(SQLITE_STATUS_SCRATCH_SIZE, n);
 361     sqlite3_mutex_leave(mem0.mutex);
 362   }else{
 363     if( sqlite3GlobalConfig.bMemstat ){
 364       sqlite3StatusSet(SQLITE_STATUS_SCRATCH_SIZE, n);
 365       n = mallocWithAlarm(n, &p);
 366       if( p ) sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_OVERFLOW, n);
 367       sqlite3_mutex_leave(mem0.mutex);
 368     }else{
 369       sqlite3_mutex_leave(mem0.mutex);
 370       p = sqlite3GlobalConfig.m.xMalloc(n);
 371     }
 372     sqlite3MemdebugSetType(p, MEMTYPE_SCRATCH);
 373   }
 374   assert( sqlite3_mutex_notheld(mem0.mutex) );
 375
 376
 377 #if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
 378   /* Verify that no more than two scratch allocations per thread
 379   ** are outstanding at one time.  (This is only checked in the
 380   ** single-threaded case since checking in the multi-threaded case
 381   ** would be much more complicated.) */
 382   assert( scratchAllocOut<=1 );
 383   if( p ) scratchAllocOut++;
 384 #endif
 385
 386   return p;
 387 }
 388 void sqlite3ScratchFree(void *p){
 389   if( p ){
 390
 391 #if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
 392     /* Verify that no more than two scratch allocation per thread
 393     ** is outstanding at one time.  (This is only checked in the
 394     ** single-threaded case since checking in the multi-threaded case
 395     ** would be much more complicated.) */
 396     assert( scratchAllocOut>=1 && scratchAllocOut<=2 );
 397     scratchAllocOut--;
 398 #endif
 399
 400     if( p>=sqlite3GlobalConfig.pScratch && p<mem0.pScratchEnd ){
 401       /* Release memory from the SQLITE_CONFIG_SCRATCH allocation */
 402       ScratchFreeslot *pSlot;
 403       pSlot = (ScratchFreeslot*)p;
 404       sqlite3_mutex_enter(mem0.mutex);
 405       pSlot->pNext = mem0.pScratchFree;
 406       mem0.pScratchFree = pSlot;
 407       mem0.nScratchFree++;
 408       assert( mem0.nScratchFree <= (u32)sqlite3GlobalConfig.nScratch );
 409       sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_USED, -1);
 410       sqlite3_mutex_leave(mem0.mutex);
 411     }else{
 412       /* Release memory back to the heap */
 413       assert( sqlite3MemdebugHasType(p, MEMTYPE_SCRATCH) );
 414       assert( sqlite3MemdebugNoType(p, ~MEMTYPE_SCRATCH) );
 415       sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
 416       if( sqlite3GlobalConfig.bMemstat ){
 417         int iSize = sqlite3MallocSize(p);
 418         sqlite3_mutex_enter(mem0.mutex);
 419         sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_OVERFLOW, -iSize);
 420         sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -iSize);
 421         sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, -1);
 422         sqlite3GlobalConfig.m.xFree(p);
 423         sqlite3_mutex_leave(mem0.mutex);
 424       }else{
 425         sqlite3GlobalConfig.m.xFree(p);
 426       }
 427     }
 428   }
 429 }
 430
 431 /*
 432 ** TRUE if p is a lookaside memory allocation from db
 433 */
 434 #ifndef SQLITE_OMIT_LOOKASIDE
 435 static int isLookaside(sqlite3 *db, void *p){
 436   return p>=db->lookaside.pStart && p<db->lookaside.pEnd;
 437 }
 438 #else
 439 #define isLookaside(A,B) 0
 440 #endif
 441
 442 /*
 443 ** Return the size of a memory allocation previously obtained from
 444 ** sqlite3Malloc() or sqlite3_malloc().
 445 */
 446 int sqlite3MallocSize(void *p){
 447   assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
 448   assert( sqlite3MemdebugNoType(p, MEMTYPE_DB) );
 449   return sqlite3GlobalConfig.m.xSize(p);
 450 }
 451 int sqlite3DbMallocSize(sqlite3 *db, void *p){
 452   assert( db!=0 );
 453   assert( sqlite3_mutex_held(db->mutex) );
 454   if( isLookaside(db, p) ){
 455     return db->lookaside.sz;
 456   }else{
 457     assert( sqlite3MemdebugHasType(p, MEMTYPE_DB) );
 458     assert( sqlite3MemdebugHasType(p, MEMTYPE_LOOKASIDE|MEMTYPE_HEAP) );
 459     assert( db!=0 || sqlite3MemdebugNoType(p, MEMTYPE_LOOKASIDE) );
 460     return sqlite3GlobalConfig.m.xSize(p);
 461   }
 462 }
 463
 464 /*
 465 ** Free memory previously obtained from sqlite3Malloc().
 466 */
 467 void sqlite3_free(void *p){
 468   if( p==0 ) return;  /* IMP: R-49053-54554 */
 469   assert( sqlite3MemdebugNoType(p, MEMTYPE_DB) );
 470   assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
 471   if( sqlite3GlobalConfig.bMemstat ){
 472     sqlite3_mutex_enter(mem0.mutex);
 473     sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -sqlite3MallocSize(p));
 474     sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, -1);
 475     sqlite3GlobalConfig.m.xFree(p);
 476     sqlite3_mutex_leave(mem0.mutex);
 477   }else{
 478     sqlite3GlobalConfig.m.xFree(p);
 479   }
 480 }
 481
 482 /*
 483 ** Free memory that might be associated with a particular database
 484 ** connection.
 485 */
 486 void sqlite3DbFree(sqlite3 *db, void *p){
 487   assert( db==0 || sqlite3_mutex_held(db->mutex) );
 488   if( p==0 ) return;
 489   if( db ){
 490     if( db->pnBytesFreed ){
 491       *db->pnBytesFreed += sqlite3DbMallocSize(db, p);
 492       return;
 493     }
 494     if( isLookaside(db, p) ){
 495       LookasideSlot *pBuf = (LookasideSlot*)p;
 496 #if SQLITE_DEBUG
 497       /* Trash all content in the buffer being freed */
 498       memset(p, 0xaa, db->lookaside.sz);
 499 #endif
 500       pBuf->pNext = db->lookaside.pFree;
 501       db->lookaside.pFree = pBuf;
 502       db->lookaside.nOut--;
 503       return;
 504     }
 505   }
 506   assert( sqlite3MemdebugHasType(p, MEMTYPE_DB) );
 507   assert( sqlite3MemdebugHasType(p, MEMTYPE_LOOKASIDE|MEMTYPE_HEAP) );
 508   assert( db!=0 || sqlite3MemdebugNoType(p, MEMTYPE_LOOKASIDE) );
 509   sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
 510   sqlite3_free(p);
 511 }
 512
 513 /*
 514 ** Change the size of an existing memory allocation
 515 */
 516 void *sqlite3Realloc(void *pOld, int nBytes){
 517   int nOld, nNew, nDiff;
 518   void *pNew;
 519   if( pOld==0 ){
 520     return sqlite3Malloc(nBytes); /* IMP: R-28354-25769 */
 521   }
 522   if( nBytes<=0 ){
 523     sqlite3_free(pOld); /* IMP: R-31593-10574 */
 524     return 0;
 525   }
 526   if( nBytes>=0x7fffff00 ){
 527     /* The 0x7ffff00 limit term is explained in comments on sqlite3Malloc() */
 528     return 0;
 529   }
 530   nOld = sqlite3MallocSize(pOld);
 531   /* IMPLEMENTATION-OF: R-46199-30249 SQLite guarantees that the second
 532   ** argument to xRealloc is always a value returned by a prior call to
 533   ** xRoundup. */
 534   nNew = sqlite3GlobalConfig.m.xRoundup(nBytes);
 535   if( nOld==nNew ){
 536     pNew = pOld;
 537   }else if( sqlite3GlobalConfig.bMemstat ){
 538     sqlite3_mutex_enter(mem0.mutex);
 539     sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, nBytes);
 540     nDiff = nNew - nOld;
 541     if( sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED) >=
 542           mem0.alarmThreshold-nDiff ){
 543       sqlite3MallocAlarm(nDiff);
 544     }
 545     assert( sqlite3MemdebugHasType(pOld, MEMTYPE_HEAP) );
 546     assert( sqlite3MemdebugNoType(pOld, ~MEMTYPE_HEAP) );
 547     pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
 548     if( pNew==0 && mem0.alarmCallback ){
 549       sqlite3MallocAlarm(nBytes);
 550       pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
 551     }
 552     if( pNew ){
 553       nNew = sqlite3MallocSize(pNew);
 554       sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, nNew-nOld);
 555     }
 556     sqlite3_mutex_leave(mem0.mutex);
 557   }else{
 558     pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
 559   }
 560   assert( EIGHT_BYTE_ALIGNMENT(pNew) ); /* IMP: R-04675-44850 */
 561   return pNew;
 562 }
 563
 564 /*
 565 ** The public interface to sqlite3Realloc.  Make sure that the memory
 566 ** subsystem is initialized prior to invoking sqliteRealloc.
 567 */
 568 void *sqlite3_realloc(void *pOld, int n){
 569 #ifndef SQLITE_OMIT_AUTOINIT
 570   if( sqlite3_initialize() ) return 0;
 571 #endif
 572   return sqlite3Realloc(pOld, n);
 573 }
 574
 575
 576 /*
 577 ** Allocate and zero memory.
 578 */
 579 void *sqlite3MallocZero(int n){
 580   void *p = sqlite3Malloc(n);
 581   if( p ){
 582     memset(p, 0, n);
 583   }
 584   return p;
 585 }
 586
 587 /*
 588 ** Allocate and zero memory.  If the allocation fails, make
 589 ** the mallocFailed flag in the connection pointer.
 590 */
 591 void *sqlite3DbMallocZero(sqlite3 *db, int n){
 592   void *p = sqlite3DbMallocRaw(db, n);
 593   if( p ){
 594     memset(p, 0, n);
 595   }
 596   return p;
 597 }
 598
 599 /*
 600 ** Allocate and zero memory.  If the allocation fails, make
 601 ** the mallocFailed flag in the connection pointer.
 602 **
 603 ** If db!=0 and db->mallocFailed is true (indicating a prior malloc
 604 ** failure on the same database connection) then always return 0.
 605 ** Hence for a particular database connection, once malloc starts
 606 ** failing, it fails consistently until mallocFailed is reset.
 607 ** This is an important assumption.  There are many places in the
 608 ** code that do things like this:
 609 **
 610 **         int *a = (int*)sqlite3DbMallocRaw(db, 100);
 611 **         int *b = (int*)sqlite3DbMallocRaw(db, 200);
 612 **         if( b ) a[10] = 9;
 613 **
 614 ** In other words, if a subsequent malloc (ex: "b") worked, it is assumed
 615 ** that all prior mallocs (ex: "a") worked too.
 616 */
 617 void *sqlite3DbMallocRaw(sqlite3 *db, int n){
 618   void *p;
 619   assert( db==0 || sqlite3_mutex_held(db->mutex) );
 620   assert( db==0 || db->pnBytesFreed==0 );
 621 #ifndef SQLITE_OMIT_LOOKASIDE
 622   if( db ){
 623     LookasideSlot *pBuf;
 624     if( db->mallocFailed ){
 625       return 0;
 626     }
 627     if( db->lookaside.bEnabled ){
 628       if( n>db->lookaside.sz ){
 629         db->lookaside.anStat[1]++;
 630       }else if( (pBuf = db->lookaside.pFree)==0 ){
 631         db->lookaside.anStat[2]++;
 632       }else{
 633         db->lookaside.pFree = pBuf->pNext;
 634         db->lookaside.nOut++;
 635         db->lookaside.anStat[0]++;
 636         if( db->lookaside.nOut>db->lookaside.mxOut ){
 637           db->lookaside.mxOut = db->lookaside.nOut;
 638         }
 639         return (void*)pBuf;
 640       }
 641     }
 642   }
 643 #else
 644   if( db && db->mallocFailed ){
 645     return 0;
 646   }
 647 #endif
 648   p = sqlite3Malloc(n);
 649   if( !p && db ){
 650     db->mallocFailed = 1;
 651   }
 652   sqlite3MemdebugSetType(p, MEMTYPE_DB |
 653          ((db && db->lookaside.bEnabled) ? MEMTYPE_LOOKASIDE : MEMTYPE_HEAP));
 654   return p;
 655 }
 656
 657 /*
 658 ** Resize the block of memory pointed to by p to n bytes. If the
 659 ** resize fails, set the mallocFailed flag in the connection object.
 660 */
 661 void *sqlite3DbRealloc(sqlite3 *db, void *p, int n){
 662   void *pNew = 0;
 663   assert( db!=0 );
 664   assert( sqlite3_mutex_held(db->mutex) );
 665   if( db->mallocFailed==0 ){
 666     if( p==0 ){
 667       return sqlite3DbMallocRaw(db, n);
 668     }
 669     if( isLookaside(db, p) ){
 670       if( n<=db->lookaside.sz ){
 671         return p;
 672       }
 673       pNew = sqlite3DbMallocRaw(db, n);
 674       if( pNew ){
 675         memcpy(pNew, p, db->lookaside.sz);
 676         sqlite3DbFree(db, p);
 677       }
 678     }else{
 679       assert( sqlite3MemdebugHasType(p, MEMTYPE_DB) );
 680       assert( sqlite3MemdebugHasType(p, MEMTYPE_LOOKASIDE|MEMTYPE_HEAP) );
 681       sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
 682       pNew = sqlite3_realloc(p, n);
 683       if( !pNew ){
 684         sqlite3MemdebugSetType(p, MEMTYPE_DB|MEMTYPE_HEAP);
 685         db->mallocFailed = 1;
 686       }
 687       sqlite3MemdebugSetType(pNew, MEMTYPE_DB |
 688             (db->lookaside.bEnabled ? MEMTYPE_LOOKASIDE : MEMTYPE_HEAP));
 689     }
 690   }
 691   return pNew;
 692 }
 693
 694 /*
 695 ** Attempt to reallocate p.  If the reallocation fails, then free p
 696 ** and set the mallocFailed flag in the database connection.
 697 */
 698 void *sqlite3DbReallocOrFree(sqlite3 *db, void *p, int n){
 699   void *pNew;
 700   pNew = sqlite3DbRealloc(db, p, n);
 701   if( !pNew ){
 702     sqlite3DbFree(db, p);
 703   }
 704   return pNew;
 705 }
 706
 707 /*
 708 ** Make a copy of a string in memory obtained from sqliteMalloc(). These
 709 ** functions call sqlite3MallocRaw() directly instead of sqliteMalloc(). This
 710 ** is because when memory debugging is turned on, these two functions are
 711 ** called via macros that record the current file and line number in the
 712 ** ThreadData structure.
 713 */
 714 char *sqlite3DbStrDup(sqlite3 *db, const char *z){
 715   char *zNew;
 716   size_t n;
 717   if( z==0 ){
 718     return 0;
 719   }
 720   n = sqlite3Strlen30(z) + 1;
 721   assert( (n&0x7fffffff)==n );
 722   zNew = sqlite3DbMallocRaw(db, (int)n);
 723   if( zNew ){
 724     memcpy(zNew, z, n);
 725   }
 726   return zNew;
 727 }
 728 char *sqlite3DbStrNDup(sqlite3 *db, const char *z, int n){
 729   char *zNew;
 730   if( z==0 ){
 731     return 0;
 732   }
 733   assert( (n&0x7fffffff)==n );
 734   zNew = sqlite3DbMallocRaw(db, n+1);
 735   if( zNew ){
 736     memcpy(zNew, z, n);
 737     zNew[n] = 0;
 738   }
 739   return zNew;
 740 }
 741
 742 /*
 743 ** Create a string from the zFromat argument and the va_list that follows.
 744 ** Store the string in memory obtained from sqliteMalloc() and make *pz
 745 ** point to that string.
 746 */
 747 void sqlite3SetString(char **pz, sqlite3 *db, const char *zFormat, ...){
 748   va_list ap;
 749   char *z;
 750
 751   va_start(ap, zFormat);
 752   z = sqlite3VMPrintf(db, zFormat, ap);
 753   va_end(ap);
 754   sqlite3DbFree(db, *pz);
 755   *pz = z;
 756 }
 757
 758
 759 /*
 760 ** This function must be called before exiting any API function (i.e.
 761 ** returning control to the user) that has called sqlite3_malloc or
 762 ** sqlite3_realloc.
 763 **
 764 ** The returned value is normally a copy of the second argument to this
 765 ** function. However, if a malloc() failure has occurred since the previous
 766 ** invocation SQLITE_NOMEM is returned instead.
 767 **
 768 ** If the first argument, db, is not NULL and a malloc() error has occurred,
 769 ** then the connection error-code (the value returned by sqlite3_errcode())
 770 ** is set to SQLITE_NOMEM.
 771 */
 772 int sqlite3ApiExit(sqlite3* db, int rc){
 773   /* If the db handle is not NULL, then we must hold the connection handle
 774   ** mutex here. Otherwise the read (and possible write) of db->mallocFailed
 775   ** is unsafe, as is the call to sqlite3Error().
 776   */
 777   assert( !db || sqlite3_mutex_held(db->mutex) );
 778   if( db && (db->mallocFailed || rc==SQLITE_IOERR_NOMEM) ){
 779     sqlite3Error(db, SQLITE_NOMEM, 0);
 780     db->mallocFailed = 0;
 781     rc = SQLITE_NOMEM;
 782   }
 783   return rc & (db ? db->errMask : 0xff);
 784 }