Many hyperlinks are disabled.
Use anonymous login
to enable hyperlinks.
Overview
Comment: | Mem3.c enhanced so that an allocation of N bytes only requires (N+11)&~7 bytes instead of (N+15)&~7 bytes of heap storage. Minimum heap usage per allocation is still 16 bytes. 8-byte alignment is preserved. (CVS 4644) |
---|---|
Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA1: |
d027f91cea0a6fd1e04d2b3853f21348 |
User & Date: | drh 2007-12-29 13:18:22.000 |
Context
2007-12-29
| ||
13:39 | Add experimental pragma "quick_check", a reduced version of integrity_check that runs without most of the overhead of the full integrity_check. (CVS 4645) (check-in: 2ddc8d7272 user: danielk1977 tags: trunk) | |
13:18 | Mem3.c enhanced so that an allocation of N bytes only requires (N+11)&~7 bytes instead of (N+15)&~7 bytes of heap storage. Minimum heap usage per allocation is still 16 bytes. 8-byte alignment is preserved. (CVS 4644) (check-in: d027f91cea user: drh tags: trunk) | |
2007-12-27
| ||
15:12 | Fix a race condition that can occur when reloading the database schema in shared-cache mode. (CVS 4643) (check-in: b37babef91 user: danielk1977 tags: trunk) | |
Changes
Changes to src/mem3.c.
︙ | ︙ | |||
16 17 18 19 20 21 22 | ** use of malloc(). All dynamically allocatable memory is ** contained in a static array, mem.aPool[]. The size of this ** fixed memory pool is SQLITE_MEMORY_SIZE bytes. ** ** This version of the memory allocation subsystem is used if ** and only if SQLITE_MEMORY_SIZE is defined. ** | | | 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | ** use of malloc(). All dynamically allocatable memory is ** contained in a static array, mem.aPool[]. The size of this ** fixed memory pool is SQLITE_MEMORY_SIZE bytes. ** ** This version of the memory allocation subsystem is used if ** and only if SQLITE_MEMORY_SIZE is defined. ** ** $Id: mem3.c,v 1.8 2007/12/29 13:18:22 drh Exp $ */ /* ** This version of the memory allocator is used only when ** SQLITE_MEMORY_SIZE is defined. */ #if defined(SQLITE_MEMORY_SIZE) |
︙ | ︙ | |||
47 48 49 50 51 52 53 | /* ** A memory allocation (also called a "chunk") consists of two or ** more blocks where each block is 8 bytes. The first 8 bytes are ** a header that is not returned to the user. ** ** A chunk is two or more blocks that is either checked out or | | | > > | > | > > | > | | | | | 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 | /* ** A memory allocation (also called a "chunk") consists of two or ** more blocks where each block is 8 bytes. The first 8 bytes are ** a header that is not returned to the user. ** ** A chunk is two or more blocks that is either checked out or ** free. The first block has format u.hdr. u.hdr.size4x is 4 times the ** size of the allocation in blocks if the allocation is free. ** The u.hdr.size4x&1 bit is true if the chunk is checked out and ** false if the chunk is on the freelist. The u.hdr.size4x&2 bit ** is true if the previous chunk is checked out and false if the ** previous chunk is free. The u.hdr.prevSize field is the size of ** the previous chunk in blocks if the previous chunk is on the ** freelist. If the previous chunk is checked out, then ** u.hdr.prevSize can be part of the data for that chunk and should ** not be read or written. ** ** We often identify a chunk by its index in mem.aPool[]. When ** this is done, the chunk index refers to the second block of ** the chunk. In this way, the first chunk has an index of 1. ** A chunk index of 0 means "no such chunk" and is the equivalent ** of a NULL pointer. ** ** The second block of free chunks is of the form u.list. The ** two fields form a double-linked list of chunks of related sizes. ** Pointers to the head of the list are stored in mem.aiSmall[] ** for smaller chunks and mem.aiHash[] for larger chunks. ** ** The second block of a chunk is user data if the chunk is checked ** out. If a chunk is checked out, the user data may extend into ** the u.hdr.prevSize value of the following chunk. */ typedef struct Mem3Block Mem3Block; struct Mem3Block { union { struct { u32 prevSize; /* Size of previous chunk in Mem3Block elements */ u32 size4x; /* 4x the size of current chunk in Mem3Block elements */ } hdr; struct { u32 next; /* Index in mem.aPool[] of next free chunk */ u32 prev; /* Index in mem.aPool[] of previous free chunk */ } list; } u; }; /* ** All of the static variables used by this module are collected ** into a single structure named "mem". This is to keep the |
︙ | ︙ | |||
101 102 103 104 105 106 107 | ** Mutex to control access to the memory allocation subsystem. */ sqlite3_mutex *mutex; /* ** The minimum amount of free space that we have seen. */ | | | | | | | | | | | > > | | | | > > | | > | 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 | ** Mutex to control access to the memory allocation subsystem. */ sqlite3_mutex *mutex; /* ** The minimum amount of free space that we have seen. */ u32 mnMaster; /* ** iMaster is the index of the master chunk. Most new allocations ** occur off of this chunk. szMaster is the size (in Mem3Blocks) ** of the current master. iMaster is 0 if there is not master chunk. ** The master chunk is not in either the aiHash[] or aiSmall[]. */ u32 iMaster; u32 szMaster; /* ** Array of lists of free blocks according to the block size ** for smaller chunks, or a hash on the block size for larger ** chunks. */ u32 aiSmall[MX_SMALL-1]; /* For sizes 2 through MX_SMALL, inclusive */ u32 aiHash[N_HASH]; /* For sizes MX_SMALL+1 and larger */ /* ** Memory available for allocation */ Mem3Block aPool[SQLITE_MEMORY_SIZE/sizeof(Mem3Block)+2]; } mem; /* ** Unlink the chunk at mem.aPool[i] from list it is currently ** on. *pRoot is the list that i is a member of. */ static void memsys3UnlinkFromList(u32 i, u32 *pRoot){ u32 next = mem.aPool[i].u.list.next; u32 prev = mem.aPool[i].u.list.prev; assert( sqlite3_mutex_held(mem.mutex) ); if( prev==0 ){ *pRoot = next; }else{ mem.aPool[prev].u.list.next = next; } if( next ){ mem.aPool[next].u.list.prev = prev; } mem.aPool[i].u.list.next = 0; mem.aPool[i].u.list.prev = 0; } /* ** Unlink the chunk at index i from ** whatever list is currently a member of. */ static void memsys3Unlink(u32 i){ u32 size, hash; assert( sqlite3_mutex_held(mem.mutex) ); assert( (mem.aPool[i-1].u.hdr.size4x & 1)==0 ); assert( i>=1 ); size = mem.aPool[i-1].u.hdr.size4x/4; assert( size==mem.aPool[i+size-1].u.hdr.prevSize ); assert( size>=2 ); if( size <= MX_SMALL ){ memsys3UnlinkFromList(i, &mem.aiSmall[size-2]); }else{ hash = size % N_HASH; memsys3UnlinkFromList(i, &mem.aiHash[hash]); } } /* ** Link the chunk at mem.aPool[i] so that is on the list rooted ** at *pRoot. */ static void memsys3LinkIntoList(u32 i, u32 *pRoot){ assert( sqlite3_mutex_held(mem.mutex) ); mem.aPool[i].u.list.next = *pRoot; mem.aPool[i].u.list.prev = 0; if( *pRoot ){ mem.aPool[*pRoot].u.list.prev = i; } *pRoot = i; } /* ** Link the chunk at index i into either the appropriate ** small chunk list, or into the large chunk hash table. */ static void memsys3Link(u32 i){ u32 size, hash; assert( sqlite3_mutex_held(mem.mutex) ); assert( i>=1 ); assert( (mem.aPool[i-1].u.hdr.size4x & 1)==0 ); size = mem.aPool[i-1].u.hdr.size4x/4; assert( size==mem.aPool[i+size-1].u.hdr.prevSize ); assert( size>=2 ); if( size <= MX_SMALL ){ memsys3LinkIntoList(i, &mem.aiSmall[size-2]); }else{ hash = size % N_HASH; memsys3LinkIntoList(i, &mem.aiHash[hash]); } } /* ** Enter the mutex mem.mutex. Allocate it if it is not already allocated. ** ** Also: Initialize the memory allocation subsystem the first time ** this routine is called. */ static void memsys3Enter(void){ if( mem.mutex==0 ){ mem.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MEM); mem.aPool[0].u.hdr.size4x = SQLITE_MEMORY_SIZE/2 + 2; mem.aPool[SQLITE_MEMORY_SIZE/8].u.hdr.prevSize = SQLITE_MEMORY_SIZE/8; mem.aPool[SQLITE_MEMORY_SIZE/8].u.hdr.size4x = 1; mem.iMaster = 1; mem.szMaster = SQLITE_MEMORY_SIZE/8; mem.mnMaster = mem.szMaster; } sqlite3_mutex_enter(mem.mutex); } |
︙ | ︙ | |||
278 279 280 281 282 283 284 | /* ** Return the size of an outstanding allocation, in bytes. The ** size returned omits the 8-byte header overhead. This only ** works for chunks that are currently checked out. */ static int memsys3Size(void *p){ Mem3Block *pBlock = (Mem3Block*)p; | | | | > > | > | | > | | > | > | | 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 | /* ** Return the size of an outstanding allocation, in bytes. The ** size returned omits the 8-byte header overhead. This only ** works for chunks that are currently checked out. */ static int memsys3Size(void *p){ Mem3Block *pBlock = (Mem3Block*)p; assert( (pBlock[-1].u.hdr.size4x&1)!=0 ); return (pBlock[-1].u.hdr.size4x&~3)*2 - 4; } /* ** Chunk i is a free chunk that has been unlinked. Adjust its ** size parameters for check-out and return a pointer to the ** user portion of the chunk. */ static void *memsys3Checkout(u32 i, int nBlock){ u32 x; assert( sqlite3_mutex_held(mem.mutex) ); assert( i>=1 ); assert( mem.aPool[i-1].u.hdr.size4x/4==nBlock ); assert( mem.aPool[i+nBlock-1].u.hdr.prevSize==nBlock ); x = mem.aPool[i-1].u.hdr.size4x; mem.aPool[i-1].u.hdr.size4x = nBlock*4 | 1 | (x&2); mem.aPool[i+nBlock-1].u.hdr.prevSize = nBlock; mem.aPool[i+nBlock-1].u.hdr.size4x |= 2; return &mem.aPool[i]; } /* ** Carve a piece off of the end of the mem.iMaster free chunk. ** Return a pointer to the new allocation. Or, if the master chunk ** is not large enough, return 0. */ static void *memsys3FromMaster(int nBlock){ assert( sqlite3_mutex_held(mem.mutex) ); assert( mem.szMaster>=nBlock ); if( nBlock>=mem.szMaster-1 ){ /* Use the entire master */ void *p = memsys3Checkout(mem.iMaster, mem.szMaster); mem.iMaster = 0; mem.szMaster = 0; mem.mnMaster = 0; return p; }else{ /* Split the master block. Return the tail. */ u32 newi, x; newi = mem.iMaster + mem.szMaster - nBlock; assert( newi > mem.iMaster+1 ); mem.aPool[mem.iMaster+mem.szMaster-1].u.hdr.prevSize = nBlock; mem.aPool[mem.iMaster+mem.szMaster-1].u.hdr.size4x |= 2; mem.aPool[newi-1].u.hdr.size4x = nBlock*4 + 1; mem.szMaster -= nBlock; mem.aPool[newi-1].u.hdr.prevSize = mem.szMaster; x = mem.aPool[mem.iMaster-1].u.hdr.size4x & 2; mem.aPool[mem.iMaster-1].u.hdr.size4x = mem.szMaster*4 | x; if( mem.szMaster < mem.mnMaster ){ mem.mnMaster = mem.szMaster; } return (void*)&mem.aPool[newi]; } } |
︙ | ︙ | |||
344 345 346 347 348 349 350 | ** the current mem.iMaster with the new larger chunk. In order for ** this mem.iMaster replacement to work, the master chunk must be ** linked into the hash tables. That is not the normal state of ** affairs, of course. The calling routine must link the master ** chunk before invoking this routine, then must unlink the (possibly ** changed) master chunk once this routine has finished. */ | | | | | | > < | > | > > | | | | | 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 | ** the current mem.iMaster with the new larger chunk. In order for ** this mem.iMaster replacement to work, the master chunk must be ** linked into the hash tables. That is not the normal state of ** affairs, of course. The calling routine must link the master ** chunk before invoking this routine, then must unlink the (possibly ** changed) master chunk once this routine has finished. */ static void memsys3Merge(u32 *pRoot){ u32 iNext, prev, size, i, x; assert( sqlite3_mutex_held(mem.mutex) ); for(i=*pRoot; i>0; i=iNext){ iNext = mem.aPool[i].u.list.next; size = mem.aPool[i-1].u.hdr.size4x; assert( (size&1)==0 ); if( (size&2)==0 ){ memsys3UnlinkFromList(i, pRoot); assert( i > mem.aPool[i-1].u.hdr.prevSize ); prev = i - mem.aPool[i-1].u.hdr.prevSize; if( prev==iNext ){ iNext = mem.aPool[prev].u.list.next; } memsys3Unlink(prev); size = i + size/4 - prev; x = mem.aPool[prev-1].u.hdr.size4x & 2; mem.aPool[prev-1].u.hdr.size4x = size*4 | x; mem.aPool[prev+size-1].u.hdr.prevSize = size; memsys3Link(prev); i = prev; }else{ size /= 4; } if( size>mem.szMaster ){ mem.iMaster = i; mem.szMaster = size; } } } /* ** Return a block of memory of at least nBytes in size. ** Return NULL if unable. */ static void *memsys3Malloc(int nByte){ u32 i; int nBlock; int toFree; assert( sqlite3_mutex_held(mem.mutex) ); assert( sizeof(Mem3Block)==8 ); if( nByte<=12 ){ nBlock = 2; }else{ nBlock = (nByte + 11)/8; } assert( nBlock >= 2 ); /* STEP 1: ** Look for an entry of the correct size in either the small ** chunk table or in the large chunk hash table. This is ** successful most of the time (about 9 times out of 10). */ if( nBlock <= MX_SMALL ){ i = mem.aiSmall[nBlock-2]; if( i>0 ){ memsys3UnlinkFromList(i, &mem.aiSmall[nBlock-2]); return memsys3Checkout(i, nBlock); } }else{ int hash = nBlock % N_HASH; for(i=mem.aiHash[hash]; i>0; i=mem.aPool[i].u.list.next){ if( mem.aPool[i-1].u.hdr.size4x/4==nBlock ){ memsys3UnlinkFromList(i, &mem.aiHash[hash]); return memsys3Checkout(i, nBlock); } } } /* STEP 2: |
︙ | ︙ | |||
459 460 461 462 463 464 465 | /* ** Free an outstanding memory allocation. */ void memsys3Free(void *pOld){ Mem3Block *p = (Mem3Block*)pOld; int i; | | > | | < | > | > | > | | | | 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 | /* ** Free an outstanding memory allocation. */ void memsys3Free(void *pOld){ Mem3Block *p = (Mem3Block*)pOld; int i; u32 size, x; assert( sqlite3_mutex_held(mem.mutex) ); assert( p>mem.aPool && p<&mem.aPool[SQLITE_MEMORY_SIZE/8] ); i = p - mem.aPool; assert( (mem.aPool[i-1].u.hdr.size4x&1)==1 ); size = mem.aPool[i-1].u.hdr.size4x/4; assert( i+size<=SQLITE_MEMORY_SIZE/8+1 ); mem.aPool[i-1].u.hdr.size4x &= ~1; mem.aPool[i+size-1].u.hdr.prevSize = size; mem.aPool[i+size-1].u.hdr.size4x &= ~2; memsys3Link(i); /* Try to expand the master using the newly freed chunk */ if( mem.iMaster ){ while( (mem.aPool[mem.iMaster-1].u.hdr.size4x&2)==0 ){ size = mem.aPool[mem.iMaster-1].u.hdr.prevSize; mem.iMaster -= size; mem.szMaster += size; memsys3Unlink(mem.iMaster); x = mem.aPool[mem.iMaster-1].u.hdr.size4x & 2; mem.aPool[mem.iMaster-1].u.hdr.size4x = mem.szMaster*4 | x; mem.aPool[mem.iMaster+mem.szMaster-1].u.hdr.prevSize = mem.szMaster; } x = mem.aPool[mem.iMaster-1].u.hdr.size4x & 2; while( (mem.aPool[mem.iMaster+mem.szMaster-1].u.hdr.size4x&1)==0 ){ memsys3Unlink(mem.iMaster+mem.szMaster); mem.szMaster += mem.aPool[mem.iMaster+mem.szMaster-1].u.hdr.size4x/4; mem.aPool[mem.iMaster-1].u.hdr.size4x = mem.szMaster*4 | x; mem.aPool[mem.iMaster+mem.szMaster-1].u.hdr.prevSize = mem.szMaster; } } } /* ** Allocate nBytes of memory |
︙ | ︙ | |||
554 555 556 557 558 559 560 | /* ** Open the file indicated and write a log of all unfreed memory ** allocations into that log. */ void sqlite3_memdebug_dump(const char *zFilename){ #ifdef SQLITE_DEBUG FILE *out; | | > | | | | > > > > > | < | | | > | > | 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 | /* ** Open the file indicated and write a log of all unfreed memory ** allocations into that log. */ void sqlite3_memdebug_dump(const char *zFilename){ #ifdef SQLITE_DEBUG FILE *out; int i, j; u32 size; if( zFilename==0 || zFilename[0]==0 ){ out = stdout; }else{ out = fopen(zFilename, "w"); if( out==0 ){ fprintf(stderr, "** Unable to output memory debug output log: %s **\n", zFilename); return; } } memsys3Enter(); fprintf(out, "CHUNKS:\n"); for(i=1; i<=SQLITE_MEMORY_SIZE/8; i+=size/4){ size = mem.aPool[i-1].u.hdr.size4x; if( size/4<=1 ){ fprintf(out, "%p size error\n", &mem.aPool[i]); assert( 0 ); break; } if( (size&1)==0 && mem.aPool[i+size/4-1].u.hdr.prevSize!=size/4 ){ fprintf(out, "%p tail size does not match\n", &mem.aPool[i]); assert( 0 ); break; } if( ((mem.aPool[i+size/4-1].u.hdr.size4x&2)>>1)!=(size&1) ){ fprintf(out, "%p tail checkout bit is incorrect\n", &mem.aPool[i]); assert( 0 ); break; } if( size&1 ){ fprintf(out, "%p %6d bytes checked out\n", &mem.aPool[i], (size/4)*8-8); }else{ fprintf(out, "%p %6d bytes free%s\n", &mem.aPool[i], (size/4)*8-8, i==mem.iMaster ? " **master**" : ""); } } for(i=0; i<MX_SMALL-1; i++){ if( mem.aiSmall[i]==0 ) continue; fprintf(out, "small(%2d):", i); for(j = mem.aiSmall[i]; j>0; j=mem.aPool[j].u.list.next){ fprintf(out, " %p(%d)", &mem.aPool[j], (mem.aPool[j-1].u.hdr.size4x/4)*8-8); } fprintf(out, "\n"); } for(i=0; i<N_HASH; i++){ if( mem.aiHash[i]==0 ) continue; fprintf(out, "hash(%2d):", i); for(j = mem.aiHash[i]; j>0; j=mem.aPool[j].u.list.next){ fprintf(out, " %p(%d)", &mem.aPool[j], (mem.aPool[j-1].u.hdr.size4x/4)*8-8); } fprintf(out, "\n"); } fprintf(out, "master=%d\n", mem.iMaster); fprintf(out, "nowUsed=%d\n", SQLITE_MEMORY_SIZE - mem.szMaster*8); fprintf(out, "mxUsed=%d\n", SQLITE_MEMORY_SIZE - mem.mnMaster*8); sqlite3_mutex_leave(mem.mutex); |
︙ | ︙ |