src/mem5.c

   1 /*
   2 ** 2007 October 14
   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 ** This file contains the C functions that implement a memory
  13 ** allocation subsystem for use by SQLite.
  14 **
  15 ** This version of the memory allocation subsystem omits all
  16 ** use of malloc(). The application gives SQLite a block of memory
  17 ** before calling sqlite3_initialize() from which allocations
  18 ** are made and returned by the xMalloc() and xRealloc()
  19 ** implementations. Once sqlite3_initialize() has been called,
  20 ** the amount of memory available to SQLite is fixed and cannot
  21 ** be changed.
  22 **
  23 ** This version of the memory allocation subsystem is included
  24 ** in the build only if SQLITE_ENABLE_MEMSYS5 is defined.
  25 **
  26 ** This memory allocator uses the following algorithm:
  27 **
  28 **   1.  All memory allocation sizes are rounded up to a power of 2.
  29 **
  30 **   2.  If two adjacent free blocks are the halves of a larger block,
  31 **       then the two blocks are coalesced into the single larger block.
  32 **
  33 **   3.  New memory is allocated from the first available free block.
  34 **
  35 ** This algorithm is described in: J. M. Robson. "Bounds for Some Functions
  36 ** Concerning Dynamic Storage Allocation". Journal of the Association for
  37 ** Computing Machinery, Volume 21, Number 8, July 1974, pages 491-499.
  38 **
  39 ** Let n be the size of the largest allocation divided by the minimum
  40 ** allocation size (after rounding all sizes up to a power of 2.)  Let M
  41 ** be the maximum amount of memory ever outstanding at one time.  Let
  42 ** N be the total amount of memory available for allocation.  Robson
  43 ** proved that this memory allocator will never breakdown due to
  44 ** fragmentation as long as the following constraint holds:
  45 **
  46 **      N >=  M*(1 + log2(n)/2) - n + 1
  47 **
  48 ** The sqlite3_status() logic tracks the maximum values of n and M so
  49 ** that an application can, at any time, verify this constraint.
  50 */
  51 #include "sqliteInt.h"
  52
  53 /*
  54 ** This version of the memory allocator is used only when
  55 ** SQLITE_ENABLE_MEMSYS5 is defined.
  56 */
  57 #ifdef SQLITE_ENABLE_MEMSYS5
  58
  59 /*
  60 ** A minimum allocation is an instance of the following structure.
  61 ** Larger allocations are an array of these structures where the
  62 ** size of the array is a power of 2.
  63 **
  64 ** The size of this object must be a power of two.  That fact is
  65 ** verified in memsys5Init().
  66 */
  67 typedef struct Mem5Link Mem5Link;
  68 struct Mem5Link {
  69   int next;       /* Index of next free chunk */
  70   int prev;       /* Index of previous free chunk */
  71 };
  72
  73 /*
  74 ** Maximum size of any allocation is ((1<<LOGMAX)*mem5.szAtom). Since
  75 ** mem5.szAtom is always at least 8 and 32-bit integers are used,
  76 ** it is not actually possible to reach this limit.
  77 */
  78 #define LOGMAX 30
  79
  80 /*
  81 ** Masks used for mem5.aCtrl[] elements.
  82 */
  83 #define CTRL_LOGSIZE  0x1f    /* Log2 Size of this block */
  84 #define CTRL_FREE     0x20    /* True if not checked out */
  85
  86 /*
  87 ** All of the static variables used by this module are collected
  88 ** into a single structure named "mem5".  This is to keep the
  89 ** static variables organized and to reduce namespace pollution
  90 ** when this module is combined with other in the amalgamation.
  91 */
  92 static SQLITE_WSD struct Mem5Global {
  93   /*
  94   ** Memory available for allocation
  95   */
  96   int szAtom;      /* Smallest possible allocation in bytes */
  97   int nBlock;      /* Number of szAtom sized blocks in zPool */
  98   u8 *zPool;       /* Memory available to be allocated */
  99
 100   /*
 101   ** Mutex to control access to the memory allocation subsystem.
 102   */
 103   sqlite3_mutex *mutex;
 104
 105 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 106   /*
 107   ** Performance statistics
 108   */
 109   u64 nAlloc;         /* Total number of calls to malloc */
 110   u64 totalAlloc;     /* Total of all malloc calls - includes internal frag */
 111   u64 totalExcess;    /* Total internal fragmentation */
 112   u32 currentOut;     /* Current checkout, including internal fragmentation */
 113   u32 currentCount;   /* Current number of distinct checkouts */
 114   u32 maxOut;         /* Maximum instantaneous currentOut */
 115   u32 maxCount;       /* Maximum instantaneous currentCount */
 116   u32 maxRequest;     /* Largest allocation (exclusive of internal frag) */
 117 #endif
 118
 119   /*
 120   ** Lists of free blocks.  aiFreelist[0] is a list of free blocks of
 121   ** size mem5.szAtom.  aiFreelist[1] holds blocks of size szAtom*2.
 122   ** aiFreelist[2] holds free blocks of size szAtom*4.  And so forth.
 123   */
 124   int aiFreelist[LOGMAX+1];
 125
 126   /*
 127   ** Space for tracking which blocks are checked out and the size
 128   ** of each block.  One byte per block.
 129   */
 130   u8 *aCtrl;
 131
 132 } mem5;
 133
 134 /*
 135 ** Access the static variable through a macro for SQLITE_OMIT_WSD.
 136 */
 137 #define mem5 GLOBAL(struct Mem5Global, mem5)
 138
 139 /*
 140 ** Assuming mem5.zPool is divided up into an array of Mem5Link
 141 ** structures, return a pointer to the idx-th such link.
 142 */
 143 #define MEM5LINK(idx) ((Mem5Link *)(&mem5.zPool[(idx)*mem5.szAtom]))
 144
 145 /*
 146 ** Unlink the chunk at mem5.aPool[i] from list it is currently
 147 ** on.  It should be found on mem5.aiFreelist[iLogsize].
 148 */
 149 static void memsys5Unlink(int i, int iLogsize){
 150   int next, prev;
 151   assert( i>=0 && i<mem5.nBlock );
 152   assert( iLogsize>=0 && iLogsize<=LOGMAX );
 153   assert( (mem5.aCtrl[i] & CTRL_LOGSIZE)==iLogsize );
 154
 155   next = MEM5LINK(i)->next;
 156   prev = MEM5LINK(i)->prev;
 157   if( prev<0 ){
 158     mem5.aiFreelist[iLogsize] = next;
 159   }else{
 160     MEM5LINK(prev)->next = next;
 161   }
 162   if( next>=0 ){
 163     MEM5LINK(next)->prev = prev;
 164   }
 165 }
 166
 167 /*
 168 ** Link the chunk at mem5.aPool[i] so that is on the iLogsize
 169 ** free list.
 170 */
 171 static void memsys5Link(int i, int iLogsize){
 172   int x;
 173   assert( sqlite3_mutex_held(mem5.mutex) );
 174   assert( i>=0 && i<mem5.nBlock );
 175   assert( iLogsize>=0 && iLogsize<=LOGMAX );
 176   assert( (mem5.aCtrl[i] & CTRL_LOGSIZE)==iLogsize );
 177
 178   x = MEM5LINK(i)->next = mem5.aiFreelist[iLogsize];
 179   MEM5LINK(i)->prev = -1;
 180   if( x>=0 ){
 181     assert( x<mem5.nBlock );
 182     MEM5LINK(x)->prev = i;
 183   }
 184   mem5.aiFreelist[iLogsize] = i;
 185 }
 186
 187 /*
 188 ** Obtain or release the mutex needed to access global data structures.
 189 */
 190 static void memsys5Enter(void){
 191   sqlite3_mutex_enter(mem5.mutex);
 192 }
 193 static void memsys5Leave(void){
 194   sqlite3_mutex_leave(mem5.mutex);
 195 }
 196
 197 /*
 198 ** Return the size of an outstanding allocation, in bytes.
 199 ** This only works for chunks that are currently checked out.
 200 */
 201 static int memsys5Size(void *p){
 202   int iSize, i;
 203   assert( p!=0 );
 204   i = (int)(((u8 *)p-mem5.zPool)/mem5.szAtom);
 205   assert( i>=0 && i<mem5.nBlock );
 206   iSize = mem5.szAtom * (1 << (mem5.aCtrl[i]&CTRL_LOGSIZE));
 207   return iSize;
 208 }
 209
 210 /*
 211 ** Return a block of memory of at least nBytes in size.
 212 ** Return NULL if unable.  Return NULL if nBytes==0.
 213 **
 214 ** The caller guarantees that nByte is positive.
 215 **
 216 ** The caller has obtained a mutex prior to invoking this
 217 ** routine so there is never any chance that two or more
 218 ** threads can be in this routine at the same time.
 219 */
 220 static void *memsys5MallocUnsafe(int nByte){
 221   int i;           /* Index of a mem5.aPool[] slot */
 222   int iBin;        /* Index into mem5.aiFreelist[] */
 223   int iFullSz;     /* Size of allocation rounded up to power of 2 */
 224   int iLogsize;    /* Log2 of iFullSz/POW2_MIN */
 225
 226   /* nByte must be a positive */
 227   assert( nByte>0 );
 228
 229   /* No more than 1GiB per allocation */
 230   if( nByte > 0x40000000 ) return 0;
 231
 232 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 233   /* Keep track of the maximum allocation request.  Even unfulfilled
 234   ** requests are counted */
 235   if( (u32)nByte>mem5.maxRequest ){
 236     mem5.maxRequest = nByte;
 237   }
 238 #endif
 239
 240
 241   /* Round nByte up to the next valid power of two */
 242   for(iFullSz=mem5.szAtom,iLogsize=0; iFullSz<nByte; iFullSz*=2,iLogsize++){}
 243
 244   /* Make sure mem5.aiFreelist[iLogsize] contains at least one free
 245   ** block.  If not, then split a block of the next larger power of
 246   ** two in order to create a new free block of size iLogsize.
 247   */
 248   for(iBin=iLogsize; iBin<=LOGMAX && mem5.aiFreelist[iBin]<0; iBin++){}
 249   if( iBin>LOGMAX ){
 250     testcase( sqlite3GlobalConfig.xLog!=0 );
 251     sqlite3_log(SQLITE_NOMEM, "failed to allocate %u bytes", nByte);
 252     return 0;
 253   }
 254   i = mem5.aiFreelist[iBin];
 255   memsys5Unlink(i, iBin);
 256   while( iBin>iLogsize ){
 257     int newSize;
 258
 259     iBin--;
 260     newSize = 1 << iBin;
 261     mem5.aCtrl[i+newSize] = CTRL_FREE | iBin;
 262     memsys5Link(i+newSize, iBin);
 263   }
 264   mem5.aCtrl[i] = iLogsize;
 265
 266 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 267   /* Update allocator performance statistics. */
 268   mem5.nAlloc++;
 269   mem5.totalAlloc += iFullSz;
 270   mem5.totalExcess += iFullSz - nByte;
 271   mem5.currentCount++;
 272   mem5.currentOut += iFullSz;
 273   if( mem5.maxCount<mem5.currentCount ) mem5.maxCount = mem5.currentCount;
 274   if( mem5.maxOut<mem5.currentOut ) mem5.maxOut = mem5.currentOut;
 275 #endif
 276
 277 #ifdef SQLITE_DEBUG
 278   /* Make sure the allocated memory does not assume that it is set to zero
 279   ** or retains a value from a previous allocation */
 280   memset(&mem5.zPool[i*mem5.szAtom], 0xAA, iFullSz);
 281 #endif
 282
 283   /* Return a pointer to the allocated memory. */
 284   return (void*)&mem5.zPool[i*mem5.szAtom];
 285 }
 286
 287 /*
 288 ** Free an outstanding memory allocation.
 289 */
 290 static void memsys5FreeUnsafe(void *pOld){
 291   u32 size, iLogsize;
 292   int iBlock;
 293
 294   /* Set iBlock to the index of the block pointed to by pOld in
 295   ** the array of mem5.szAtom byte blocks pointed to by mem5.zPool.
 296   */
 297   iBlock = (int)(((u8 *)pOld-mem5.zPool)/mem5.szAtom);
 298
 299   /* Check that the pointer pOld points to a valid, non-free block. */
 300   assert( iBlock>=0 && iBlock<mem5.nBlock );
 301   assert( ((u8 *)pOld-mem5.zPool)%mem5.szAtom==0 );
 302   assert( (mem5.aCtrl[iBlock] & CTRL_FREE)==0 );
 303
 304   iLogsize = mem5.aCtrl[iBlock] & CTRL_LOGSIZE;
 305   size = 1<<iLogsize;
 306   assert( iBlock+size-1<(u32)mem5.nBlock );
 307
 308   mem5.aCtrl[iBlock] |= CTRL_FREE;
 309   mem5.aCtrl[iBlock+size-1] |= CTRL_FREE;
 310
 311 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 312   assert( mem5.currentCount>0 );
 313   assert( mem5.currentOut>=(size*mem5.szAtom) );
 314   mem5.currentCount--;
 315   mem5.currentOut -= size*mem5.szAtom;
 316   assert( mem5.currentOut>0 || mem5.currentCount==0 );
 317   assert( mem5.currentCount>0 || mem5.currentOut==0 );
 318 #endif
 319
 320   mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;
 321   while( ALWAYS(iLogsize<LOGMAX) ){
 322     int iBuddy;
 323     if( (iBlock>>iLogsize) & 1 ){
 324       iBuddy = iBlock - size;
 325       assert( iBuddy>=0 );
 326     }else{
 327       iBuddy = iBlock + size;
 328       if( iBuddy>=mem5.nBlock ) break;
 329     }
 330     if( mem5.aCtrl[iBuddy]!=(CTRL_FREE | iLogsize) ) break;
 331     memsys5Unlink(iBuddy, iLogsize);
 332     iLogsize++;
 333     if( iBuddy<iBlock ){
 334       mem5.aCtrl[iBuddy] = CTRL_FREE | iLogsize;
 335       mem5.aCtrl[iBlock] = 0;
 336       iBlock = iBuddy;
 337     }else{
 338       mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;
 339       mem5.aCtrl[iBuddy] = 0;
 340     }
 341     size *= 2;
 342   }
 343
 344 #ifdef SQLITE_DEBUG
 345   /* Overwrite freed memory with the 0x55 bit pattern to verify that it is
 346   ** not used after being freed */
 347   memset(&mem5.zPool[iBlock*mem5.szAtom], 0x55, size);
 348 #endif
 349
 350   memsys5Link(iBlock, iLogsize);
 351 }
 352
 353 /*
 354 ** Allocate nBytes of memory.
 355 */
 356 static void *memsys5Malloc(int nBytes){
 357   sqlite3_int64 *p = 0;
 358   if( nBytes>0 ){
 359     memsys5Enter();
 360     p = memsys5MallocUnsafe(nBytes);
 361     memsys5Leave();
 362   }
 363   return (void*)p;
 364 }
 365
 366 /*
 367 ** Free memory.
 368 **
 369 ** The outer layer memory allocator prevents this routine from
 370 ** being called with pPrior==0.
 371 */
 372 static void memsys5Free(void *pPrior){
 373   assert( pPrior!=0 );
 374   memsys5Enter();
 375   memsys5FreeUnsafe(pPrior);
 376   memsys5Leave();
 377 }
 378
 379 /*
 380 ** Change the size of an existing memory allocation.
 381 **
 382 ** The outer layer memory allocator prevents this routine from
 383 ** being called with pPrior==0.
 384 **
 385 ** nBytes is always a value obtained from a prior call to
 386 ** memsys5Round().  Hence nBytes is always a non-negative power
 387 ** of two.  If nBytes==0 that means that an oversize allocation
 388 ** (an allocation larger than 0x40000000) was requested and this
 389 ** routine should return 0 without freeing pPrior.
 390 */
 391 static void *memsys5Realloc(void *pPrior, int nBytes){
 392   int nOld;
 393   void *p;
 394   assert( pPrior!=0 );
 395   assert( (nBytes&(nBytes-1))==0 );  /* EV: R-46199-30249 */
 396   assert( nBytes>=0 );
 397   if( nBytes==0 ){
 398     return 0;
 399   }
 400   nOld = memsys5Size(pPrior);
 401   if( nBytes<=nOld ){
 402     return pPrior;
 403   }
 404   p = memsys5Malloc(nBytes);
 405   if( p ){
 406     memcpy(p, pPrior, nOld);
 407     memsys5Free(pPrior);
 408   }
 409   return p;
 410 }
 411
 412 /*
 413 ** Round up a request size to the next valid allocation size.  If
 414 ** the allocation is too large to be handled by this allocation system,
 415 ** return 0.
 416 **
 417 ** All allocations must be a power of two and must be expressed by a
 418 ** 32-bit signed integer.  Hence the largest allocation is 0x40000000
 419 ** or 1073741824 bytes.
 420 */
 421 static int memsys5Roundup(int n){
 422   int iFullSz;
 423   if( n > 0x40000000 ) return 0;
 424   for(iFullSz=mem5.szAtom; iFullSz<n; iFullSz *= 2);
 425   return iFullSz;
 426 }
 427
 428 /*
 429 ** Return the ceiling of the logarithm base 2 of iValue.
 430 **
 431 ** Examples:   memsys5Log(1) -> 0
 432 **             memsys5Log(2) -> 1
 433 **             memsys5Log(4) -> 2
 434 **             memsys5Log(5) -> 3
 435 **             memsys5Log(8) -> 3
 436 **             memsys5Log(9) -> 4
 437 */
 438 static int memsys5Log(int iValue){
 439   int iLog;
 440   for(iLog=0; (iLog<(int)((sizeof(int)*8)-1)) && (1<<iLog)<iValue; iLog++);
 441   return iLog;
 442 }
 443
 444 /*
 445 ** Initialize the memory allocator.
 446 **
 447 ** This routine is not threadsafe.  The caller must be holding a mutex
 448 ** to prevent multiple threads from entering at the same time.
 449 */
 450 static int memsys5Init(void *NotUsed){
 451   int ii;            /* Loop counter */
 452   int nByte;         /* Number of bytes of memory available to this allocator */
 453   u8 *zByte;         /* Memory usable by this allocator */
 454   int nMinLog;       /* Log base 2 of minimum allocation size in bytes */
 455   int iOffset;       /* An offset into mem5.aCtrl[] */
 456
 457   UNUSED_PARAMETER(NotUsed);
 458
 459   /* For the purposes of this routine, disable the mutex */
 460   mem5.mutex = 0;
 461
 462   /* The size of a Mem5Link object must be a power of two.  Verify that
 463   ** this is case.
 464   */
 465   assert( (sizeof(Mem5Link)&(sizeof(Mem5Link)-1))==0 );
 466
 467   nByte = sqlite3GlobalConfig.nHeap;
 468   zByte = (u8*)sqlite3GlobalConfig.pHeap;
 469   assert( zByte!=0 );  /* sqlite3_config() does not allow otherwise */
 470
 471   /* boundaries on sqlite3GlobalConfig.mnReq are enforced in sqlite3_config() */
 472   nMinLog = memsys5Log(sqlite3GlobalConfig.mnReq);
 473   mem5.szAtom = (1<<nMinLog);
 474   while( (int)sizeof(Mem5Link)>mem5.szAtom ){
 475     mem5.szAtom = mem5.szAtom << 1;
 476   }
 477
 478   mem5.nBlock = (nByte / (mem5.szAtom+sizeof(u8)));
 479   mem5.zPool = zByte;
 480   mem5.aCtrl = (u8 *)&mem5.zPool[mem5.nBlock*mem5.szAtom];
 481
 482   for(ii=0; ii<=LOGMAX; ii++){
 483     mem5.aiFreelist[ii] = -1;
 484   }
 485
 486   iOffset = 0;
 487   for(ii=LOGMAX; ii>=0; ii--){
 488     int nAlloc = (1<<ii);
 489     if( (iOffset+nAlloc)<=mem5.nBlock ){
 490       mem5.aCtrl[iOffset] = ii | CTRL_FREE;
 491       memsys5Link(iOffset, ii);
 492       iOffset += nAlloc;
 493     }
 494     assert((iOffset+nAlloc)>mem5.nBlock);
 495   }
 496
 497   /* If a mutex is required for normal operation, allocate one */
 498   if( sqlite3GlobalConfig.bMemstat==0 ){
 499     mem5.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
 500   }
 501
 502   return SQLITE_OK;
 503 }
 504
 505 /*
 506 ** Deinitialize this module.
 507 */
 508 static void memsys5Shutdown(void *NotUsed){
 509   UNUSED_PARAMETER(NotUsed);
 510   mem5.mutex = 0;
 511   return;
 512 }
 513
 514 #ifdef SQLITE_TEST
 515 /*
 516 ** Open the file indicated and write a log of all unfreed memory
 517 ** allocations into that log.
 518 */
 519 void sqlite3Memsys5Dump(const char *zFilename){
 520   FILE *out;
 521   int i, j, n;
 522   int nMinLog;
 523
 524   if( zFilename==0 || zFilename[0]==0 ){
 525     out = stdout;
 526   }else{
 527     out = fopen(zFilename, "w");
 528     if( out==0 ){
 529       fprintf(stderr, "** Unable to output memory debug output log: %s **\n",
 530                       zFilename);
 531       return;
 532     }
 533   }
 534   memsys5Enter();
 535   nMinLog = memsys5Log(mem5.szAtom);
 536   for(i=0; i<=LOGMAX && i+nMinLog<32; i++){
 537     for(n=0, j=mem5.aiFreelist[i]; j>=0; j = MEM5LINK(j)->next, n++){}
 538     fprintf(out, "freelist items of size %d: %d\n", mem5.szAtom << i, n);
 539   }
 540   fprintf(out, "mem5.nAlloc       = %llu\n", mem5.nAlloc);
 541   fprintf(out, "mem5.totalAlloc   = %llu\n", mem5.totalAlloc);
 542   fprintf(out, "mem5.totalExcess  = %llu\n", mem5.totalExcess);
 543   fprintf(out, "mem5.currentOut   = %u\n", mem5.currentOut);
 544   fprintf(out, "mem5.currentCount = %u\n", mem5.currentCount);
 545   fprintf(out, "mem5.maxOut       = %u\n", mem5.maxOut);
 546   fprintf(out, "mem5.maxCount     = %u\n", mem5.maxCount);
 547   fprintf(out, "mem5.maxRequest   = %u\n", mem5.maxRequest);
 548   memsys5Leave();
 549   if( out==stdout ){
 550     fflush(stdout);
 551   }else{
 552     fclose(out);
 553   }
 554 }
 555 #endif
 556
 557 /*
 558 ** This routine is the only routine in this file with external
 559 ** linkage. It returns a pointer to a static sqlite3_mem_methods
 560 ** struct populated with the memsys5 methods.
 561 */
 562 const sqlite3_mem_methods *sqlite3MemGetMemsys5(void){
 563   static const sqlite3_mem_methods memsys5Methods = {
 564      memsys5Malloc,
 565      memsys5Free,
 566      memsys5Realloc,
 567      memsys5Size,
 568      memsys5Roundup,
 569      memsys5Init,
 570      memsys5Shutdown,
 571      0
 572   };
 573   return &memsys5Methods;
 574 }
 575
 576 #endif /* SQLITE_ENABLE_MEMSYS5 */