sqlcipher/src/mem3.c at Xcode5 · securitykernel/sqlcipher · GitHub

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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,

};

return &mempoolMethods;

}

#endif /* SQLITE_ENABLE_MEMSYS3 */

sqlcipher/src/mem3.c at Xcode5 · securitykernel/sqlcipher · GitHub

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