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687 lines (640 loc) · 19.8 KB
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/*
** 2007 October 14
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement a memory
** allocation subsystem for use by SQLite.
**
** This version of the memory allocation subsystem omits all
** use of malloc(). The SQLite user supplies a block of memory
** before calling sqlite3_initialize() from which allocations
** are made and returned by the xMalloc() and xRealloc()
** implementations. Once sqlite3_initialize() has been called,
** the amount of memory available to SQLite is fixed and cannot
** be changed.
**
** This version of the memory allocation subsystem is included
** in the build only if SQLITE_ENABLE_MEMSYS3 is defined.
*/
#include "sqliteInt.h"
/*
** This version of the memory allocator is only built into the library
** SQLITE_ENABLE_MEMSYS3 is defined. Defining this symbol does not
** mean that the library will use a memory-pool by default, just that
** it is available. The mempool allocator is activated by calling
** sqlite3_config().
*/
#ifdef SQLITE_ENABLE_MEMSYS3
/*
** Maximum size (in Mem3Blocks) of a "small" chunk.
*/
#define MX_SMALL 10
/*
** Number of freelist hash slots
*/
#define N_HASH 61
/*
** 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 mem3.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 mem3.aiSmall[]
** for smaller chunks and mem3.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 mem3.aPool[] of next free chunk */
u32 prev; /* Index in mem3.aPool[] of previous free chunk */
} list;
} u;
};
/*
** All of the static variables used by this module are collected
** into a single structure named "mem3". This is to keep the
** static variables organized and to reduce namespace pollution
** when this module is combined with other in the amalgamation.
*/
static SQLITE_WSD struct Mem3Global {
/*
** Memory available for allocation. nPool is the size of the array
** (in Mem3Blocks) pointed to by aPool less 2.
*/
u32 nPool;
Mem3Block *aPool;
/*
** True if we are evaluating an out-of-memory callback.
*/
int alarmBusy;
/*
** 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 */
} mem3 = { 97535575 };
#define mem3 GLOBAL(struct Mem3Global, mem3)
/*
** Unlink the chunk at mem3.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 = mem3.aPool[i].u.list.next;
u32 prev = mem3.aPool[i].u.list.prev;
assert( sqlite3_mutex_held(mem3.mutex) );
if( prev==0 ){
*pRoot = next;
}else{
mem3.aPool[prev].u.list.next = next;
}
if( next ){
mem3.aPool[next].u.list.prev = prev;
}
mem3.aPool[i].u.list.next = 0;
mem3.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(mem3.mutex) );
assert( (mem3.aPool[i-1].u.hdr.size4x & 1)==0 );
assert( i>=1 );
size = mem3.aPool[i-1].u.hdr.size4x/4;
assert( size==mem3.aPool[i+size-1].u.hdr.prevSize );
assert( size>=2 );
if( size <= MX_SMALL ){
memsys3UnlinkFromList(i, &mem3.aiSmall[size-2]);
}else{
hash = size % N_HASH;
memsys3UnlinkFromList(i, &mem3.aiHash[hash]);
}
}
/*
** Link the chunk at mem3.aPool[i] so that is on the list rooted
** at *pRoot.
*/
static void memsys3LinkIntoList(u32 i, u32 *pRoot){
assert( sqlite3_mutex_held(mem3.mutex) );
mem3.aPool[i].u.list.next = *pRoot;
mem3.aPool[i].u.list.prev = 0;
if( *pRoot ){
mem3.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(mem3.mutex) );
assert( i>=1 );
assert( (mem3.aPool[i-1].u.hdr.size4x & 1)==0 );
size = mem3.aPool[i-1].u.hdr.size4x/4;
assert( size==mem3.aPool[i+size-1].u.hdr.prevSize );
assert( size>=2 );
if( size <= MX_SMALL ){
memsys3LinkIntoList(i, &mem3.aiSmall[size-2]);
}else{
hash = size % N_HASH;
memsys3LinkIntoList(i, &mem3.aiHash[hash]);
}
}
/*
** If the STATIC_MEM mutex is not already held, obtain it now. The mutex
** will already be held (obtained by code in malloc.c) if
** sqlite3GlobalConfig.bMemStat is true.
*/
static void memsys3Enter(void){
if( sqlite3GlobalConfig.bMemstat==0 && mem3.mutex==0 ){
mem3.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
}
sqlite3_mutex_enter(mem3.mutex);
}
static void memsys3Leave(void){
sqlite3_mutex_leave(mem3.mutex);
}
/*
** Called when we are unable to satisfy an allocation of nBytes.
*/
static void memsys3OutOfMemory(int nByte){
if( !mem3.alarmBusy ){
mem3.alarmBusy = 1;
assert( sqlite3_mutex_held(mem3.mutex) );
sqlite3_mutex_leave(mem3.mutex);
sqlite3_release_memory(nByte);
sqlite3_mutex_enter(mem3.mutex);
mem3.alarmBusy = 0;
}
}
/*
** 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, u32 nBlock){
u32 x;
assert( sqlite3_mutex_held(mem3.mutex) );
assert( i>=1 );
assert( mem3.aPool[i-1].u.hdr.size4x/4==nBlock );
assert( mem3.aPool[i+nBlock-1].u.hdr.prevSize==nBlock );
x = mem3.aPool[i-1].u.hdr.size4x;
mem3.aPool[i-1].u.hdr.size4x = nBlock*4 | 1 | (x&2);
mem3.aPool[i+nBlock-1].u.hdr.prevSize = nBlock;
mem3.aPool[i+nBlock-1].u.hdr.size4x |= 2;
return &mem3.aPool[i];
}
/*
** Carve a piece off of the end of the mem3.iMaster free chunk.
** Return a pointer to the new allocation. Or, if the master chunk
** is not large enough, return 0.
*/
static void *memsys3FromMaster(u32 nBlock){
assert( sqlite3_mutex_held(mem3.mutex) );
assert( mem3.szMaster>=nBlock );
if( nBlock>=mem3.szMaster-1 ){
/* Use the entire master */
void *p = memsys3Checkout(mem3.iMaster, mem3.szMaster);
mem3.iMaster = 0;
mem3.szMaster = 0;
mem3.mnMaster = 0;
return p;
}else{
/* Split the master block. Return the tail. */
u32 newi, x;
newi = mem3.iMaster + mem3.szMaster - nBlock;
assert( newi > mem3.iMaster+1 );
mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.prevSize = nBlock;
mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.size4x |= 2;
mem3.aPool[newi-1].u.hdr.size4x = nBlock*4 + 1;
mem3.szMaster -= nBlock;
mem3.aPool[newi-1].u.hdr.prevSize = mem3.szMaster;
x = mem3.aPool[mem3.iMaster-1].u.hdr.size4x & 2;
mem3.aPool[mem3.iMaster-1].u.hdr.size4x = mem3.szMaster*4 | x;
if( mem3.szMaster < mem3.mnMaster ){
mem3.mnMaster = mem3.szMaster;
}
return (void*)&mem3.aPool[newi];
}
}
/*
** *pRoot is the head of a list of free chunks of the same size
** or same size hash. In other words, *pRoot is an entry in either
** mem3.aiSmall[] or mem3.aiHash[].
**
** This routine examines all entries on the given list and tries
** to coalesce each entries with adjacent free chunks.
**
** If it sees a chunk that is larger than mem3.iMaster, it replaces
** the current mem3.iMaster with the new larger chunk. In order for
** this mem3.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(mem3.mutex) );
for(i=*pRoot; i>0; i=iNext){
iNext = mem3.aPool[i].u.list.next;
size = mem3.aPool[i-1].u.hdr.size4x;
assert( (size&1)==0 );
if( (size&2)==0 ){
memsys3UnlinkFromList(i, pRoot);
assert( i > mem3.aPool[i-1].u.hdr.prevSize );
prev = i - mem3.aPool[i-1].u.hdr.prevSize;
if( prev==iNext ){
iNext = mem3.aPool[prev].u.list.next;
}
memsys3Unlink(prev);
size = i + size/4 - prev;
x = mem3.aPool[prev-1].u.hdr.size4x & 2;
mem3.aPool[prev-1].u.hdr.size4x = size*4 | x;
mem3.aPool[prev+size-1].u.hdr.prevSize = size;
memsys3Link(prev);
i = prev;
}else{
size /= 4;
}
if( size>mem3.szMaster ){
mem3.iMaster = i;
mem3.szMaster = size;
}
}
}
/*
** Return a block of memory of at least nBytes in size.
** Return NULL if unable.
**
** This function assumes that the necessary mutexes, if any, are
** already held by the caller. Hence "Unsafe".
*/
static void *memsys3MallocUnsafe(int nByte){
u32 i;
u32 nBlock;
u32 toFree;
assert( sqlite3_mutex_held(mem3.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 = mem3.aiSmall[nBlock-2];
if( i>0 ){
memsys3UnlinkFromList(i, &mem3.aiSmall[nBlock-2]);
return memsys3Checkout(i, nBlock);
}
}else{
int hash = nBlock % N_HASH;
for(i=mem3.aiHash[hash]; i>0; i=mem3.aPool[i].u.list.next){
if( mem3.aPool[i-1].u.hdr.size4x/4==nBlock ){
memsys3UnlinkFromList(i, &mem3.aiHash[hash]);
return memsys3Checkout(i, nBlock);
}
}
}
/* STEP 2:
** Try to satisfy the allocation by carving a piece off of the end
** of the master chunk. This step usually works if step 1 fails.
*/
if( mem3.szMaster>=nBlock ){
return memsys3FromMaster(nBlock);
}
/* STEP 3:
** Loop through the entire memory pool. Coalesce adjacent free
** chunks. Recompute the master chunk as the largest free chunk.
** Then try again to satisfy the allocation by carving a piece off
** of the end of the master chunk. This step happens very
** rarely (we hope!)
*/
for(toFree=nBlock*16; toFree<(mem3.nPool*16); toFree *= 2){
memsys3OutOfMemory(toFree);
if( mem3.iMaster ){
memsys3Link(mem3.iMaster);
mem3.iMaster = 0;
mem3.szMaster = 0;
}
for(i=0; i<N_HASH; i++){
memsys3Merge(&mem3.aiHash[i]);
}
for(i=0; i<MX_SMALL-1; i++){
memsys3Merge(&mem3.aiSmall[i]);
}
if( mem3.szMaster ){
memsys3Unlink(mem3.iMaster);
if( mem3.szMaster>=nBlock ){
return memsys3FromMaster(nBlock);
}
}
}
/* If none of the above worked, then we fail. */
return 0;
}
/*
** Free an outstanding memory allocation.
**
** This function assumes that the necessary mutexes, if any, are
** already held by the caller. Hence "Unsafe".
*/
static void memsys3FreeUnsafe(void *pOld){
Mem3Block *p = (Mem3Block*)pOld;
int i;
u32 size, x;
assert( sqlite3_mutex_held(mem3.mutex) );
assert( p>mem3.aPool && p<&mem3.aPool[mem3.nPool] );
i = p - mem3.aPool;
assert( (mem3.aPool[i-1].u.hdr.size4x&1)==1 );
size = mem3.aPool[i-1].u.hdr.size4x/4;
assert( i+size<=mem3.nPool+1 );
mem3.aPool[i-1].u.hdr.size4x &= ~1;
mem3.aPool[i+size-1].u.hdr.prevSize = size;
mem3.aPool[i+size-1].u.hdr.size4x &= ~2;
memsys3Link(i);
/* Try to expand the master using the newly freed chunk */
if( mem3.iMaster ){
while( (mem3.aPool[mem3.iMaster-1].u.hdr.size4x&2)==0 ){
size = mem3.aPool[mem3.iMaster-1].u.hdr.prevSize;
mem3.iMaster -= size;
mem3.szMaster += size;
memsys3Unlink(mem3.iMaster);
x = mem3.aPool[mem3.iMaster-1].u.hdr.size4x & 2;
mem3.aPool[mem3.iMaster-1].u.hdr.size4x = mem3.szMaster*4 | x;
mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.prevSize = mem3.szMaster;
}
x = mem3.aPool[mem3.iMaster-1].u.hdr.size4x & 2;
while( (mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.size4x&1)==0 ){
memsys3Unlink(mem3.iMaster+mem3.szMaster);
mem3.szMaster += mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.size4x/4;
mem3.aPool[mem3.iMaster-1].u.hdr.size4x = mem3.szMaster*4 | x;
mem3.aPool[mem3.iMaster+mem3.szMaster-1].u.hdr.prevSize = mem3.szMaster;
}
}
}
/*
** 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;
if( p==0 ) return 0;
pBlock = (Mem3Block*)p;
assert( (pBlock[-1].u.hdr.size4x&1)!=0 );
return (pBlock[-1].u.hdr.size4x&~3)*2 - 4;
}
/*
** Round up a request size to the next valid allocation size.
*/
static int memsys3Roundup(int n){
if( n<=12 ){
return 12;
}else{
return ((n+11)&~7) - 4;
}
}
/*
** Allocate nBytes of memory.
*/
static void *memsys3Malloc(int nBytes){
sqlite3_int64 *p;
assert( nBytes>0 ); /* malloc.c filters out 0 byte requests */
memsys3Enter();
p = memsys3MallocUnsafe(nBytes);
memsys3Leave();
return (void*)p;
}
/*
** Free memory.
*/
static void memsys3Free(void *pPrior){
assert( pPrior );
memsys3Enter();
memsys3FreeUnsafe(pPrior);
memsys3Leave();
}
/*
** Change the size of an existing memory allocation
*/
static void *memsys3Realloc(void *pPrior, int nBytes){
int nOld;
void *p;
if( pPrior==0 ){
return sqlite3_malloc(nBytes);
}
if( nBytes<=0 ){
sqlite3_free(pPrior);
return 0;
}
nOld = memsys3Size(pPrior);
if( nBytes<=nOld && nBytes>=nOld-128 ){
return pPrior;
}
memsys3Enter();
p = memsys3MallocUnsafe(nBytes);
if( p ){
if( nOld<nBytes ){
memcpy(p, pPrior, nOld);
}else{
memcpy(p, pPrior, nBytes);
}
memsys3FreeUnsafe(pPrior);
}
memsys3Leave();
return p;
}
/*
** Initialize this module.
*/
static int memsys3Init(void *NotUsed){
UNUSED_PARAMETER(NotUsed);
if( !sqlite3GlobalConfig.pHeap ){
return SQLITE_ERROR;
}
/* Store a pointer to the memory block in global structure mem3. */
assert( sizeof(Mem3Block)==8 );
mem3.aPool = (Mem3Block *)sqlite3GlobalConfig.pHeap;
mem3.nPool = (sqlite3GlobalConfig.nHeap / sizeof(Mem3Block)) - 2;
/* Initialize the master block. */
mem3.szMaster = mem3.nPool;
mem3.mnMaster = mem3.szMaster;
mem3.iMaster = 1;
mem3.aPool[0].u.hdr.size4x = (mem3.szMaster<<2) + 2;
mem3.aPool[mem3.nPool].u.hdr.prevSize = mem3.nPool;
mem3.aPool[mem3.nPool].u.hdr.size4x = 1;
return SQLITE_OK;
}
/*
** Deinitialize this module.
*/
static void memsys3Shutdown(void *NotUsed){
UNUSED_PARAMETER(NotUsed);
mem3.mutex = 0;
return;
}
/*
** Open the file indicated and write a log of all unfreed memory
** allocations into that log.
*/
void sqlite3Memsys3Dump(const char *zFilename){
#ifdef SQLITE_DEBUG
FILE *out;
u32 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<=mem3.nPool; i+=size/4){
size = mem3.aPool[i-1].u.hdr.size4x;
if( size/4<=1 ){
fprintf(out, "%p size error\n", &mem3.aPool[i]);
assert( 0 );
break;
}
if( (size&1)==0 && mem3.aPool[i+size/4-1].u.hdr.prevSize!=size/4 ){
fprintf(out, "%p tail size does not match\n", &mem3.aPool[i]);
assert( 0 );
break;
}
if( ((mem3.aPool[i+size/4-1].u.hdr.size4x&2)>>1)!=(size&1) ){
fprintf(out, "%p tail checkout bit is incorrect\n", &mem3.aPool[i]);
assert( 0 );
break;
}
if( size&1 ){
fprintf(out, "%p %6d bytes checked out\n", &mem3.aPool[i], (size/4)*8-8);
}else{
fprintf(out, "%p %6d bytes free%s\n", &mem3.aPool[i], (size/4)*8-8,
i==mem3.iMaster ? " **master**" : "");
}
}
for(i=0; i<MX_SMALL-1; i++){
if( mem3.aiSmall[i]==0 ) continue;
fprintf(out, "small(%2d):", i);
for(j = mem3.aiSmall[i]; j>0; j=mem3.aPool[j].u.list.next){
fprintf(out, " %p(%d)", &mem3.aPool[j],
(mem3.aPool[j-1].u.hdr.size4x/4)*8-8);
}
fprintf(out, "\n");
}
for(i=0; i<N_HASH; i++){
if( mem3.aiHash[i]==0 ) continue;
fprintf(out, "hash(%2d):", i);
for(j = mem3.aiHash[i]; j>0; j=mem3.aPool[j].u.list.next){
fprintf(out, " %p(%d)", &mem3.aPool[j],
(mem3.aPool[j-1].u.hdr.size4x/4)*8-8);
}
fprintf(out, "\n");
}
fprintf(out, "master=%d\n", mem3.iMaster);
fprintf(out, "nowUsed=%d\n", mem3.nPool*8 - mem3.szMaster*8);
fprintf(out, "mxUsed=%d\n", mem3.nPool*8 - mem3.mnMaster*8);
sqlite3_mutex_leave(mem3.mutex);
if( out==stdout ){
fflush(stdout);
}else{
fclose(out);
}
#else
UNUSED_PARAMETER(zFilename);
#endif
}
/*
** This routine is the only routine in this file with external
** linkage.
**
** Populate the low-level memory allocation function pointers in
** sqlite3GlobalConfig.m with pointers to the routines in this file. The
** arguments specify the block of memory to manage.
**
** This routine is only called by sqlite3_config(), and therefore
** is not required to be threadsafe (it is not).
*/
const sqlite3_mem_methods *sqlite3MemGetMemsys3(void){
static const sqlite3_mem_methods mempoolMethods = {
memsys3Malloc,
memsys3Free,
memsys3Realloc,
memsys3Size,
memsys3Roundup,
memsys3Init,
memsys3Shutdown,
0
};
return &mempoolMethods;
}
#endif /* SQLITE_ENABLE_MEMSYS3 */