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(u64 n){
 298   void *p;
 299   if( n==0 || n>=0x7fffff00 ){
 300     /* A memory allocation of a number of bytes which is near the maximum
 301     ** signed integer value might cause an integer overflow inside of the
 302     ** xMalloc().  Hence we limit the maximum size to 0x7fffff00, giving
 303     ** 255 bytes of overhead.  SQLite itself will never use anything near
 304     ** this amount.  The only way to reach the limit is with sqlite3_malloc() */
 305     p = 0;
 306   }else if( sqlite3GlobalConfig.bMemstat ){
 307     sqlite3_mutex_enter(mem0.mutex);
 308     mallocWithAlarm((int)n, &p);
 309     sqlite3_mutex_leave(mem0.mutex);
 310   }else{
 311     p = sqlite3GlobalConfig.m.xMalloc((int)n);
 312   }
 313   assert( EIGHT_BYTE_ALIGNMENT(p) );  /* IMP: R-11148-40995 */
 314   return p;
 315 }
 316
 317 /*
 318 ** This version of the memory allocation is for use by the application.
 319 ** First make sure the memory subsystem is initialized, then do the
 320 ** allocation.
 321 */
 322 void *sqlite3_malloc(int n){
 323 #ifndef SQLITE_OMIT_AUTOINIT
 324   if( sqlite3_initialize() ) return 0;
 325 #endif
 326   return n<=0 ? 0 : sqlite3Malloc(n);
 327 }
 328 void *sqlite3_malloc64(sqlite3_uint64 n){
 329 #ifndef SQLITE_OMIT_AUTOINIT
 330   if( sqlite3_initialize() ) return 0;
 331 #endif
 332   return sqlite3Malloc(n);
 333 }
 334
 335 /*
 336 ** Each thread may only have a single outstanding allocation from
 337 ** xScratchMalloc().  We verify this constraint in the single-threaded
 338 ** case by setting scratchAllocOut to 1 when an allocation
 339 ** is outstanding clearing it when the allocation is freed.
 340 */
 341 #if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
 342 static int scratchAllocOut = 0;
 343 #endif
 344
 345
 346 /*
 347 ** Allocate memory that is to be used and released right away.
 348 ** This routine is similar to alloca() in that it is not intended
 349 ** for situations where the memory might be held long-term.  This
 350 ** routine is intended to get memory to old large transient data
 351 ** structures that would not normally fit on the stack of an
 352 ** embedded processor.
 353 */
 354 void *sqlite3ScratchMalloc(int n){
 355   void *p;
 356   assert( n>0 );
 357
 358   sqlite3_mutex_enter(mem0.mutex);
 359   sqlite3StatusSet(SQLITE_STATUS_SCRATCH_SIZE, n);
 360   if( mem0.nScratchFree && sqlite3GlobalConfig.szScratch>=n ){
 361     p = mem0.pScratchFree;
 362     mem0.pScratchFree = mem0.pScratchFree->pNext;
 363     mem0.nScratchFree--;
 364     sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_USED, 1);
 365     sqlite3_mutex_leave(mem0.mutex);
 366   }else{
 367     sqlite3_mutex_leave(mem0.mutex);
 368     p = sqlite3Malloc(n);
 369     if( sqlite3GlobalConfig.bMemstat && p ){
 370       sqlite3_mutex_enter(mem0.mutex);
 371       sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_OVERFLOW, sqlite3MallocSize(p));
 372       sqlite3_mutex_leave(mem0.mutex);
 373     }
 374     sqlite3MemdebugSetType(p, MEMTYPE_SCRATCH);
 375   }
 376   assert( sqlite3_mutex_notheld(mem0.mutex) );
 377
 378
 379 #if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
 380   /* EVIDENCE-OF: R-12970-05880 SQLite will not use more than one scratch
 381   ** buffers per thread.
 382   **
 383   ** This can only be checked in single-threaded mode.
 384   */
 385   assert( scratchAllocOut==0 );
 386   if( p ) scratchAllocOut++;
 387 #endif
 388
 389   return p;
 390 }
 391 void sqlite3ScratchFree(void *p){
 392   if( p ){
 393
 394 #if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
 395     /* Verify that no more than two scratch allocation per thread
 396     ** is outstanding at one time.  (This is only checked in the
 397     ** single-threaded case since checking in the multi-threaded case
 398     ** would be much more complicated.) */
 399     assert( scratchAllocOut>=1 && scratchAllocOut<=2 );
 400     scratchAllocOut--;
 401 #endif
 402
 403     if( p>=sqlite3GlobalConfig.pScratch && p<mem0.pScratchEnd ){
 404       /* Release memory from the SQLITE_CONFIG_SCRATCH allocation */
 405       ScratchFreeslot *pSlot;
 406       pSlot = (ScratchFreeslot*)p;
 407       sqlite3_mutex_enter(mem0.mutex);
 408       pSlot->pNext = mem0.pScratchFree;
 409       mem0.pScratchFree = pSlot;
 410       mem0.nScratchFree++;
 411       assert( mem0.nScratchFree <= (u32)sqlite3GlobalConfig.nScratch );
 412       sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_USED, -1);
 413       sqlite3_mutex_leave(mem0.mutex);
 414     }else{
 415       /* Release memory back to the heap */
 416       assert( sqlite3MemdebugHasType(p, MEMTYPE_SCRATCH) );
 417       assert( sqlite3MemdebugNoType(p, ~MEMTYPE_SCRATCH) );
 418       sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
 419       if( sqlite3GlobalConfig.bMemstat ){
 420         int iSize = sqlite3MallocSize(p);
 421         sqlite3_mutex_enter(mem0.mutex);
 422         sqlite3StatusAdd(SQLITE_STATUS_SCRATCH_OVERFLOW, -iSize);
 423         sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -iSize);
 424         sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, -1);
 425         sqlite3GlobalConfig.m.xFree(p);
 426         sqlite3_mutex_leave(mem0.mutex);
 427       }else{
 428         sqlite3GlobalConfig.m.xFree(p);
 429       }
 430     }
 431   }
 432 }
 433
 434 /*
 435 ** TRUE if p is a lookaside memory allocation from db
 436 */
 437 #ifndef SQLITE_OMIT_LOOKASIDE
 438 static int isLookaside(sqlite3 *db, void *p){
 439   return p>=db->lookaside.pStart && p<db->lookaside.pEnd;
 440 }
 441 #else
 442 #define isLookaside(A,B) 0
 443 #endif
 444
 445 /*
 446 ** Return the size of a memory allocation previously obtained from
 447 ** sqlite3Malloc() or sqlite3_malloc().
 448 */
 449 int sqlite3MallocSize(void *p){
 450   assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
 451   return sqlite3GlobalConfig.m.xSize(p);
 452 }
 453 int sqlite3DbMallocSize(sqlite3 *db, void *p){
 454   if( db==0 ){
 455     assert( sqlite3MemdebugNoType(p, ~MEMTYPE_HEAP) );
 456     assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
 457     return sqlite3MallocSize(p);
 458   }else{
 459     assert( sqlite3_mutex_held(db->mutex) );
 460     if( isLookaside(db, p) ){
 461       return db->lookaside.sz;
 462     }else{
 463       assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
 464       assert( sqlite3MemdebugNoType(p, ~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
 465       return sqlite3GlobalConfig.m.xSize(p);
 466     }
 467   }
 468 }
 469 sqlite3_uint64 sqlite3_msize(void *p){
 470   assert( sqlite3MemdebugNoType(p, ~MEMTYPE_HEAP) );
 471   assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
 472   return (sqlite3_uint64)sqlite3GlobalConfig.m.xSize(p);
 473 }
 474
 475 /*
 476 ** Free memory previously obtained from sqlite3Malloc().
 477 */
 478 void sqlite3_free(void *p){
 479   if( p==0 ) return;  /* IMP: R-49053-54554 */
 480   assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
 481   assert( sqlite3MemdebugNoType(p, ~MEMTYPE_HEAP) );
 482   if( sqlite3GlobalConfig.bMemstat ){
 483     sqlite3_mutex_enter(mem0.mutex);
 484     sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, -sqlite3MallocSize(p));
 485     sqlite3StatusAdd(SQLITE_STATUS_MALLOC_COUNT, -1);
 486     sqlite3GlobalConfig.m.xFree(p);
 487     sqlite3_mutex_leave(mem0.mutex);
 488   }else{
 489     sqlite3GlobalConfig.m.xFree(p);
 490   }
 491 }
 492
 493 /*
 494 ** Add the size of memory allocation "p" to the count in
 495 ** *db->pnBytesFreed.
 496 */
 497 static SQLITE_NOINLINE void measureAllocationSize(sqlite3 *db, void *p){
 498   *db->pnBytesFreed += sqlite3DbMallocSize(db,p);
 499 }
 500
 501 /*
 502 ** Free memory that might be associated with a particular database
 503 ** connection.
 504 */
 505 void sqlite3DbFree(sqlite3 *db, void *p){
 506   assert( db==0 || sqlite3_mutex_held(db->mutex) );
 507   if( p==0 ) return;
 508   if( db ){
 509     if( db->pnBytesFreed ){
 510       measureAllocationSize(db, p);
 511       return;
 512     }
 513     if( isLookaside(db, p) ){
 514       LookasideSlot *pBuf = (LookasideSlot*)p;
 515 #if SQLITE_DEBUG
 516       /* Trash all content in the buffer being freed */
 517       memset(p, 0xaa, db->lookaside.sz);
 518 #endif
 519       pBuf->pNext = db->lookaside.pFree;
 520       db->lookaside.pFree = pBuf;
 521       db->lookaside.nOut--;
 522       return;
 523     }
 524   }
 525   assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
 526   assert( sqlite3MemdebugNoType(p, ~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
 527   assert( db!=0 || sqlite3MemdebugNoType(p, MEMTYPE_LOOKASIDE) );
 528   sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
 529   sqlite3_free(p);
 530 }
 531
 532 /*
 533 ** Change the size of an existing memory allocation
 534 */
 535 void *sqlite3Realloc(void *pOld, u64 nBytes){
 536   int nOld, nNew, nDiff;
 537   void *pNew;
 538   assert( sqlite3MemdebugHasType(pOld, MEMTYPE_HEAP) );
 539   assert( sqlite3MemdebugNoType(pOld, ~MEMTYPE_HEAP) );
 540   if( pOld==0 ){
 541     return sqlite3Malloc(nBytes); /* IMP: R-04300-56712 */
 542   }
 543   if( nBytes==0 ){
 544     sqlite3_free(pOld); /* IMP: R-26507-47431 */
 545     return 0;
 546   }
 547   if( nBytes>=0x7fffff00 ){
 548     /* The 0x7ffff00 limit term is explained in comments on sqlite3Malloc() */
 549     return 0;
 550   }
 551   nOld = sqlite3MallocSize(pOld);
 552   /* IMPLEMENTATION-OF: R-46199-30249 SQLite guarantees that the second
 553   ** argument to xRealloc is always a value returned by a prior call to
 554   ** xRoundup. */
 555   nNew = sqlite3GlobalConfig.m.xRoundup((int)nBytes);
 556   if( nOld==nNew ){
 557     pNew = pOld;
 558   }else if( sqlite3GlobalConfig.bMemstat ){
 559     sqlite3_mutex_enter(mem0.mutex);
 560     sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, (int)nBytes);
 561     nDiff = nNew - nOld;
 562     if( sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED) >=
 563           mem0.alarmThreshold-nDiff ){
 564       sqlite3MallocAlarm(nDiff);
 565     }
 566     pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
 567     if( pNew==0 && mem0.alarmCallback ){
 568       sqlite3MallocAlarm((int)nBytes);
 569       pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
 570     }
 571     if( pNew ){
 572       nNew = sqlite3MallocSize(pNew);
 573       sqlite3StatusAdd(SQLITE_STATUS_MEMORY_USED, nNew-nOld);
 574     }
 575     sqlite3_mutex_leave(mem0.mutex);
 576   }else{
 577     pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
 578   }
 579   assert( EIGHT_BYTE_ALIGNMENT(pNew) ); /* IMP: R-11148-40995 */
 580   return pNew;
 581 }
 582
 583 /*
 584 ** The public interface to sqlite3Realloc.  Make sure that the memory
 585 ** subsystem is initialized prior to invoking sqliteRealloc.
 586 */
 587 void *sqlite3_realloc(void *pOld, int n){
 588 #ifndef SQLITE_OMIT_AUTOINIT
 589   if( sqlite3_initialize() ) return 0;
 590 #endif
 591   if( n<0 ) n = 0;  /* IMP: R-26507-47431 */
 592   return sqlite3Realloc(pOld, n);
 593 }
 594 void *sqlite3_realloc64(void *pOld, sqlite3_uint64 n){
 595 #ifndef SQLITE_OMIT_AUTOINIT
 596   if( sqlite3_initialize() ) return 0;
 597 #endif
 598   return sqlite3Realloc(pOld, n);
 599 }
 600
 601
 602 /*
 603 ** Allocate and zero memory.
 604 */
 605 void *sqlite3MallocZero(u64 n){
 606   void *p = sqlite3Malloc(n);
 607   if( p ){
 608     memset(p, 0, (size_t)n);
 609   }
 610   return p;
 611 }
 612
 613 /*
 614 ** Allocate and zero memory.  If the allocation fails, make
 615 ** the mallocFailed flag in the connection pointer.
 616 */
 617 void *sqlite3DbMallocZero(sqlite3 *db, u64 n){
 618   void *p = sqlite3DbMallocRaw(db, n);
 619   if( p ){
 620     memset(p, 0, (size_t)n);
 621   }
 622   return p;
 623 }
 624
 625 /*
 626 ** Allocate and zero memory.  If the allocation fails, make
 627 ** the mallocFailed flag in the connection pointer.
 628 **
 629 ** If db!=0 and db->mallocFailed is true (indicating a prior malloc
 630 ** failure on the same database connection) then always return 0.
 631 ** Hence for a particular database connection, once malloc starts
 632 ** failing, it fails consistently until mallocFailed is reset.
 633 ** This is an important assumption.  There are many places in the
 634 ** code that do things like this:
 635 **
 636 **         int *a = (int*)sqlite3DbMallocRaw(db, 100);
 637 **         int *b = (int*)sqlite3DbMallocRaw(db, 200);
 638 **         if( b ) a[10] = 9;
 639 **
 640 ** In other words, if a subsequent malloc (ex: "b") worked, it is assumed
 641 ** that all prior mallocs (ex: "a") worked too.
 642 */
 643 void *sqlite3DbMallocRaw(sqlite3 *db, u64 n){
 644   void *p;
 645   assert( db==0 || sqlite3_mutex_held(db->mutex) );
 646   assert( db==0 || db->pnBytesFreed==0 );
 647 #ifndef SQLITE_OMIT_LOOKASIDE
 648   if( db ){
 649     LookasideSlot *pBuf;
 650     if( db->mallocFailed ){
 651       return 0;
 652     }
 653     if( db->lookaside.bEnabled ){
 654       if( n>db->lookaside.sz ){
 655         db->lookaside.anStat[1]++;
 656       }else if( (pBuf = db->lookaside.pFree)==0 ){
 657         db->lookaside.anStat[2]++;
 658       }else{
 659         db->lookaside.pFree = pBuf->pNext;
 660         db->lookaside.nOut++;
 661         db->lookaside.anStat[0]++;
 662         if( db->lookaside.nOut>db->lookaside.mxOut ){
 663           db->lookaside.mxOut = db->lookaside.nOut;
 664         }
 665         return (void*)pBuf;
 666       }
 667     }
 668   }
 669 #else
 670   if( db && db->mallocFailed ){
 671     return 0;
 672   }
 673 #endif
 674   p = sqlite3Malloc(n);
 675   if( !p && db ){
 676     db->mallocFailed = 1;
 677   }
 678   sqlite3MemdebugSetType(p,
 679          (db && db->lookaside.bEnabled) ? MEMTYPE_LOOKASIDE : MEMTYPE_HEAP);
 680   return p;
 681 }
 682
 683 /*
 684 ** Resize the block of memory pointed to by p to n bytes. If the
 685 ** resize fails, set the mallocFailed flag in the connection object.
 686 */
 687 void *sqlite3DbRealloc(sqlite3 *db, void *p, u64 n){
 688   void *pNew = 0;
 689   assert( db!=0 );
 690   assert( sqlite3_mutex_held(db->mutex) );
 691   if( db->mallocFailed==0 ){
 692     if( p==0 ){
 693       return sqlite3DbMallocRaw(db, n);
 694     }
 695     if( isLookaside(db, p) ){
 696       if( n<=db->lookaside.sz ){
 697         return p;
 698       }
 699       pNew = sqlite3DbMallocRaw(db, n);
 700       if( pNew ){
 701         memcpy(pNew, p, db->lookaside.sz);
 702         sqlite3DbFree(db, p);
 703       }
 704     }else{
 705       assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
 706       assert( sqlite3MemdebugNoType(p, ~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
 707       sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
 708       pNew = sqlite3_realloc64(p, n);
 709       if( !pNew ){
 710         db->mallocFailed = 1;
 711       }
 712       sqlite3MemdebugSetType(pNew,
 713             (db->lookaside.bEnabled ? MEMTYPE_LOOKASIDE : MEMTYPE_HEAP));
 714     }
 715   }
 716   return pNew;
 717 }
 718
 719 /*
 720 ** Attempt to reallocate p.  If the reallocation fails, then free p
 721 ** and set the mallocFailed flag in the database connection.
 722 */
 723 void *sqlite3DbReallocOrFree(sqlite3 *db, void *p, u64 n){
 724   void *pNew;
 725   pNew = sqlite3DbRealloc(db, p, n);
 726   if( !pNew ){
 727     sqlite3DbFree(db, p);
 728   }
 729   return pNew;
 730 }
 731
 732 /*
 733 ** Make a copy of a string in memory obtained from sqliteMalloc(). These
 734 ** functions call sqlite3MallocRaw() directly instead of sqliteMalloc(). This
 735 ** is because when memory debugging is turned on, these two functions are
 736 ** called via macros that record the current file and line number in the
 737 ** ThreadData structure.
 738 */
 739 char *sqlite3DbStrDup(sqlite3 *db, const char *z){
 740   char *zNew;
 741   size_t n;
 742   if( z==0 ){
 743     return 0;
 744   }
 745   n = sqlite3Strlen30(z) + 1;
 746   assert( (n&0x7fffffff)==n );
 747   zNew = sqlite3DbMallocRaw(db, (int)n);
 748   if( zNew ){
 749     memcpy(zNew, z, n);
 750   }
 751   return zNew;
 752 }
 753 char *sqlite3DbStrNDup(sqlite3 *db, const char *z, u64 n){
 754   char *zNew;
 755   if( z==0 ){
 756     return 0;
 757   }
 758   assert( (n&0x7fffffff)==n );
 759   zNew = sqlite3DbMallocRaw(db, n+1);
 760   if( zNew ){
 761     memcpy(zNew, z, (size_t)n);
 762     zNew[n] = 0;
 763   }
 764   return zNew;
 765 }
 766
 767 /*
 768 ** Create a string from the zFromat argument and the va_list that follows.
 769 ** Store the string in memory obtained from sqliteMalloc() and make *pz
 770 ** point to that string.
 771 */
 772 void sqlite3SetString(char **pz, sqlite3 *db, const char *zFormat, ...){
 773   va_list ap;
 774   char *z;
 775
 776   va_start(ap, zFormat);
 777   z = sqlite3VMPrintf(db, zFormat, ap);
 778   va_end(ap);
 779   sqlite3DbFree(db, *pz);
 780   *pz = z;
 781 }
 782
 783 /*
 784 ** Take actions at the end of an API call to indicate an OOM error
 785 */
 786 static SQLITE_NOINLINE int apiOomError(sqlite3 *db){
 787   db->mallocFailed = 0;
 788   sqlite3Error(db, SQLITE_NOMEM);
 789   return SQLITE_NOMEM;
 790 }
 791
 792 /*
 793 ** This function must be called before exiting any API function (i.e.
 794 ** returning control to the user) that has called sqlite3_malloc or
 795 ** sqlite3_realloc.
 796 **
 797 ** The returned value is normally a copy of the second argument to this
 798 ** function. However, if a malloc() failure has occurred since the previous
 799 ** invocation SQLITE_NOMEM is returned instead.
 800 **
 801 ** If the first argument, db, is not NULL and a malloc() error has occurred,
 802 ** then the connection error-code (the value returned by sqlite3_errcode())
 803 ** is set to SQLITE_NOMEM.
 804 */
 805 int sqlite3ApiExit(sqlite3* db, int rc){
 806   /* If the db handle is not NULL, then we must hold the connection handle
 807   ** mutex here. Otherwise the read (and possible write) of db->mallocFailed
 808   ** is unsafe, as is the call to sqlite3Error().
 809   */
 810   assert( !db || sqlite3_mutex_held(db->mutex) );
 811   if( db==0 ) return rc & 0xff;
 812   if( db->mallocFailed || rc==SQLITE_IOERR_NOMEM ){
 813     return apiOomError(db);
 814   }
 815   return rc & db->errMask;
 816 }