/*
** 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 application gives SQLite 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_MEMSYS5 is defined.
**
** This memory allocator uses the following algorithm:
**
** 1. All memory allocations sizes are rounded up to a power of 2.
**
** 2. If two adjacent free blocks are the halves of a larger block,
** then the two blocks are coalesed into the single larger block.
**
** 3. New memory is allocated from the first available free block.
**
** This algorithm is described in: J. M. Robson. "Bounds for Some Functions
** Concerning Dynamic Storage Allocation". Journal of the Association for
** Computing Machinery, Volume 21, Number 8, July 1974, pages 491-499.
**
** Let n be the size of the largest allocation divided by the minimum
** allocation size (after rounding all sizes up to a power of 2.) Let M
** be the maximum amount of memory ever outstanding at one time. Let
** N be the total amount of memory available for allocation. Robson
** proved that this memory allocator will never breakdown due to
** fragmentation as long as the following constraint holds:
**
** N >= M*(1 + log2(n)/2) - n + 1
**
** The sqlite3_status() logic tracks the maximum values of n and M so
** that an application can, at any time, verify this constraint.
*/
#include "sqliteInt.h"
/*
** This version of the memory allocator is used only when
** SQLITE_ENABLE_MEMSYS5 is defined.
*/
#ifdef SQLITE_ENABLE_MEMSYS5
/*
** A minimum allocation is an instance of the following structure.
** Larger allocations are an array of these structures where the
** size of the array is a power of 2.
**
** The size of this object must be a power of two. That fact is
** verified in memsys5Init().
*/
typedef struct Mem5Link Mem5Link;
struct Mem5Link {
int next; /* Index of next free chunk */
int prev; /* Index of previous free chunk */
};
/*
** Maximum size of any allocation is ((1<<LOGMAX)*mem5.szAtom). Since
** mem5.szAtom is always at least 8 and 32-bit integers are used,
** it is not actually possible to reach this limit.
*/
#define LOGMAX 30
/*
** Masks used for mem5.aCtrl[] elements.
*/
#define CTRL_LOGSIZE 0x1f /* Log2 Size of this block */
#define CTRL_FREE 0x20 /* True if not checked out */
/*
** All of the static variables used by this module are collected
** into a single structure named "mem5". 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 Mem5Global {
/*
** Memory available for allocation
*/
int szAtom; /* Smallest possible allocation in bytes */
int nBlock; /* Number of szAtom sized blocks in zPool */
u8 *zPool; /* Memory available to be allocated */
/*
** Mutex to control access to the memory allocation subsystem.
*/
sqlite3_mutex *mutex;
/*
** Performance statistics
*/
u64 nAlloc; /* Total number of calls to malloc */
u64 totalAlloc; /* Total of all malloc calls - includes internal frag */
u64 totalExcess; /* Total internal fragmentation */
u32 currentOut; /* Current checkout, including internal fragmentation */
u32 currentCount; /* Current number of distinct checkouts */
u32 maxOut; /* Maximum instantaneous currentOut */
u32 maxCount; /* Maximum instantaneous currentCount */
u32 maxRequest; /* Largest allocation (exclusive of internal frag) */
/*
** Lists of free blocks. aiFreelist[0] is a list of free blocks of
** size mem5.szAtom. aiFreelist[1] holds blocks of size szAtom*2.
** and so forth.
*/
int aiFreelist[LOGMAX+1];
/*
** Space for tracking which blocks are checked out and the size
** of each block. One byte per block.
*/
u8 *aCtrl;
} mem5;
/*
** Access the static variable through a macro for SQLITE_OMIT_WSD
*/
#define mem5 GLOBAL(struct Mem5Global, mem5)
/*
** Assuming mem5.zPool is divided up into an array of Mem5Link
** structures, return a pointer to the idx-th such lik.
*/
#define MEM5LINK(idx) ((Mem5Link *)(&mem5.zPool[(idx)*mem5.szAtom]))
/*
** Unlink the chunk at mem5.aPool[i] from list it is currently
** on. It should be found on mem5.aiFreelist[iLogsize].
*/
static void memsys5Unlink(int i, int iLogsize){
int next, prev;
assert( i>=0 && i<mem5.nBlock );
assert( iLogsize>=0 && iLogsize<=LOGMAX );
assert( (mem5.aCtrl[i] & CTRL_LOGSIZE)==iLogsize );
next = MEM5LINK(i)->next;
prev = MEM5LINK(i)->prev;
if( prev<0 ){
mem5.aiFreelist[iLogsize] = next;
}else{
MEM5LINK(prev)->next = next;
}
if( next>=0 ){
MEM5LINK(next)->prev = prev;
}
}
/*
** Link the chunk at mem5.aPool[i] so that is on the iLogsize
** free list.
*/
static void memsys5Link(int i, int iLogsize){
int x;
assert( sqlite3_mutex_held(mem5.mutex) );
assert( i>=0 && i<mem5.nBlock );
assert( iLogsize>=0 && iLogsize<=LOGMAX );
assert( (mem5.aCtrl[i] & CTRL_LOGSIZE)==iLogsize );
x = MEM5LINK(i)->next = mem5.aiFreelist[iLogsize];
MEM5LINK(i)->prev = -1;
if( x>=0 ){
assert( x<mem5.nBlock );
MEM5LINK(x)->prev = i;
}
mem5.aiFreelist[iLogsize] = i;
}
/*
** 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 memsys5Enter(void){
sqlite3_mutex_enter(mem5.mutex);
}
static void memsys5Leave(void){
sqlite3_mutex_leave(mem5.mutex);
}
/*
** 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 memsys5Size(void *p){
int iSize = 0;
if( p ){
int i = ((u8 *)p-mem5.zPool)/mem5.szAtom;
assert( i>=0 && i<mem5.nBlock );
iSize = mem5.szAtom * (1 << (mem5.aCtrl[i]&CTRL_LOGSIZE));
}
return iSize;
}
/*
** Find the first entry on the freelist iLogsize. Unlink that
** entry and return its index.
*/
static int memsys5UnlinkFirst(int iLogsize){
int i;
int iFirst;
assert( iLogsize>=0 && iLogsize<=LOGMAX );
i = iFirst = mem5.aiFreelist[iLogsize];
assert( iFirst>=0 );
while( i>0 ){
if( i<iFirst ) iFirst = i;
i = MEM5LINK(i)->next;
}
memsys5Unlink(iFirst, iLogsize);
return iFirst;
}
/*
** Return a block of memory of at least nBytes in size.
** Return NULL if unable. Return NULL if nBytes==0.
**
** The caller guarantees that nByte positive.
**
** The caller has obtained a mutex prior to invoking this
** routine so there is never any chance that two or more
** threads can be in this routine at the same time.
*/
static void *memsys5MallocUnsafe(int nByte){
int i; /* Index of a mem5.aPool[] slot */
int iBin; /* Index into mem5.aiFreelist[] */
int iFullSz; /* Size of allocation rounded up to power of 2 */
int iLogsize; /* Log2 of iFullSz/POW2_MIN */
/* nByte must be a positive */
assert( nByte>0 );
/* Keep track of the maximum allocation request. Even unfulfilled
** requests are counted */
if( (u32)nByte>mem5.maxRequest ){
mem5.maxRequest = nByte;
}
/* Abort if the requested allocation size is larger than the largest
** power of two that we can represent using 32-bit signed integers.
*/
if( nByte > 0x40000000 ){
return 0;
}
/* Round nByte up to the next valid power of two */
for(iFullSz=mem5.szAtom, iLogsize=0; iFullSz<nByte; iFullSz *= 2, iLogsize++){}
/* Make sure mem5.aiFreelist[iLogsize] contains at least one free
** block. If not, then split a block of the next larger power of
** two in order to create a new free block of size iLogsize.
*/
for(iBin=iLogsize; mem5.aiFreelist[iBin]<0 && iBin<=LOGMAX; iBin++){}
if( iBin>LOGMAX ){
testcase( sqlite3GlobalConfig.xLog!=0 );
sqlite3_log(SQLITE_NOMEM, "failed to allocate %u bytes", nByte);
return 0;
}
i = memsys5UnlinkFirst(iBin);
while( iBin>iLogsize ){
int newSize;
iBin--;
newSize = 1 << iBin;
mem5.aCtrl[i+newSize] = CTRL_FREE | iBin;
memsys5Link(i+newSize, iBin);
}
mem5.aCtrl[i] = iLogsize;
/* Update allocator performance statistics. */
mem5.nAlloc++;
mem5.totalAlloc += iFullSz;
mem5.totalExcess += iFullSz - nByte;
mem5.currentCount++;
mem5.currentOut += iFullSz;
if( mem5.maxCount<mem5.currentCount ) mem5.maxCount = mem5.currentCount;
if( mem5.maxOut<mem5.currentOut ) mem5.maxOut = mem5.currentOut;
/* Return a pointer to the allocated memory. */
return (void*)&mem5.zPool[i*mem5.szAtom];
}
/*
** Free an outstanding memory allocation.
*/
static void memsys5FreeUnsafe(void *pOld){
u32 size, iLogsize;
int iBlock;
/* Set iBlock to the index of the block pointed to by pOld in
** the array of mem5.szAtom byte blocks pointed to by mem5.zPool.
*/
iBlock = ((u8 *)pOld-mem5.zPool)/mem5.szAtom;
/* Check that the pointer pOld points to a valid, non-free block. */
assert( iBlock>=0 && iBlock<mem5.nBlock );
assert( ((u8 *)pOld-mem5.zPool)%mem5.szAtom==0 );
assert( (mem5.aCtrl[iBlock] & CTRL_FREE)==0 );
iLogsize = mem5.aCtrl[iBlock] & CTRL_LOGSIZE;
size = 1<<iLogsize;
assert( iBlock+size-1<(u32)mem5.nBlock );
mem5.aCtrl[iBlock] |= CTRL_FREE;
mem5.aCtrl[iBlock+size-1] |= CTRL_FREE;
assert( mem5.currentCount>0 );
assert( mem5.currentOut>=(size*mem5.szAtom) );
mem5.currentCount--;
mem5.currentOut -= size*mem5.szAtom;
assert( mem5.currentOut>0 || mem5.currentCount==0 );
assert( mem5.currentCount>0 || mem5.currentOut==0 );
mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;
while( ALWAYS(iLogsize<LOGMAX) ){
int iBuddy;
if( (iBlock>>iLogsize) & 1 ){
iBuddy = iBlock - size;
}else{
iBuddy = iBlock + size;
}
assert( iBuddy>=0 );
if( (iBuddy+(1<<iLogsize))>mem5.nBlock ) break;
if( mem5.aCtrl[iBuddy]!=(CTRL_FREE | iLogsize) ) break;
memsys5Unlink(iBuddy, iLogsize);
iLogsize++;
if( iBuddy<iBlock ){
mem5.aCtrl[iBuddy] = CTRL_FREE | iLogsize;
mem5.aCtrl[iBlock] = 0;
iBlock = iBuddy;
}else{
mem5.aCtrl[iBlock] = CTRL_FREE | iLogsize;
mem5.aCtrl[iBuddy] = 0;
}
size *= 2;
}
memsys5Link(iBlock, iLogsize);
}
/*
** Allocate nBytes of memory
*/
static void *memsys5Malloc(int nBytes){
sqlite3_int64 *p = 0;
if( nBytes>0 ){
memsys5Enter();
p = memsys5MallocUnsafe(nBytes);
memsys5Leave();
}
return (void*)p;
}
/*
** Free memory.
**
** The outer layer memory allocator prevents this routine from
** being called with pPrior==0.
*/
static void memsys5Free(void *pPrior){
assert( pPrior!=0 );
memsys5Enter();
memsys5FreeUnsafe(pPrior);
memsys5Leave();
}
/*
** Change the size of an existing memory allocation.
**
** The outer layer memory allocator prevents this routine from
** being called with pPrior==0.
**
** nBytes is always a value obtained from a prior call to
** memsys5Round(). Hence nBytes is always a non-negative power
** of two. If nBytes==0 that means that an oversize allocation
** (an allocation larger than 0x40000000) was requested and this
** routine should return 0 without freeing pPrior.
*/
static void *memsys5Realloc(void *pPrior, int nBytes){
int nOld;
void *p;
assert( pPrior!=0 );
assert( (nBytes&(nBytes-1))==0 ); /* EV: R-46199-30249 */
assert( nBytes>=0 );
if( nBytes==0 ){
return 0;
}
nOld = memsys5Size(pPrior);
if( nBytes<=nOld ){
return pPrior;
}
memsys5Enter();
p = memsys5MallocUnsafe(nBytes);
if( p ){
memcpy(p, pPrior, nOld);
memsys5FreeUnsafe(pPrior);
}
memsys5Leave();
return p;
}
/*
** Round up a request size to the next valid allocation size. If
** the allocation is too large to be handled by this allocation system,
** return 0.
**
** All allocations must be a power of two and must be expressed by a
** 32-bit signed integer. Hence the largest allocation is 0x40000000
** or 1073741824 bytes.
*/
static int memsys5Roundup(int n){
int iFullSz;
if( n > 0x40000000 ) return 0;
for(iFullSz=mem5.szAtom; iFullSz<n; iFullSz *= 2);
return iFullSz;
}
/*
** Return the ceiling of the logarithm base 2 of iValue.
**
** Examples: memsys5Log(1) -> 0
** memsys5Log(2) -> 1
** memsys5Log(4) -> 2
** memsys5Log(5) -> 3
** memsys5Log(8) -> 3
** memsys5Log(9) -> 4
*/
static int memsys5Log(int iValue){
int iLog;
for(iLog=0; (iLog<(int)((sizeof(int)*8)-1)) && (1<<iLog)<iValue; iLog++);
return iLog;
}
/*
** Initialize the memory allocator.
**
** This routine is not threadsafe. The caller must be holding a mutex
** to prevent multiple threads from entering at the same time.
*/
static int memsys5Init(void *NotUsed){
int ii; /* Loop counter */
int nByte; /* Number of bytes of memory available to this allocator */
u8 *zByte; /* Memory usable by this allocator */
int nMinLog; /* Log base 2 of minimum allocation size in bytes */
int iOffset; /* An offset into mem5.aCtrl[] */
UNUSED_PARAMETER(NotUsed);
/* For the purposes of this routine, disable the mutex */
mem5.mutex = 0;
/* The size of a Mem5Link object must be a power of two. Verify that
** this is case.
*/
assert( (sizeof(Mem5Link)&(sizeof(Mem5Link)-1))==0 );
nByte = sqlite3GlobalConfig.nHeap;
zByte = (u8*)sqlite3GlobalConfig.pHeap;
assert( zByte!=0 ); /* sqlite3_config() does not allow otherwise */
/* boundaries on sqlite3GlobalConfig.mnReq are enforced in sqlite3_config() */
nMinLog = memsys5Log(sqlite3GlobalConfig.mnReq);
mem5.szAtom = (1<<nMinLog);
while( (int)sizeof(Mem5Link)>mem5.szAtom ){
mem5.szAtom = mem5.szAtom << 1;
}
mem5.nBlock = (nByte / (mem5.szAtom+sizeof(u8)));
mem5.zPool = zByte;
mem5.aCtrl = (u8 *)&mem5.zPool[mem5.nBlock*mem5.szAtom];
for(ii=0; ii<=LOGMAX; ii++){
mem5.aiFreelist[ii] = -1;
}
iOffset = 0;
for(ii=LOGMAX; ii>=0; ii--){
int nAlloc = (1<<ii);
if( (iOffset+nAlloc)<=mem5.nBlock ){
mem5.aCtrl[iOffset] = ii | CTRL_FREE;
memsys5Link(iOffset, ii);
iOffset += nAlloc;
}
assert((iOffset+nAlloc)>mem5.nBlock);
}
/* If a mutex is required for normal operation, allocate one */
if( sqlite3GlobalConfig.bMemstat==0 ){
mem5.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
}
return SQLITE_OK;
}
/*
** Deinitialize this module.
*/
static void memsys5Shutdown(void *NotUsed){
UNUSED_PARAMETER(NotUsed);
mem5.mutex = 0;
return;
}
#ifdef SQLITE_TEST
/*
** Open the file indicated and write a log of all unfreed memory
** allocations into that log.
*/
void sqlite3Memsys5Dump(const char *zFilename){
FILE *out;
int i, j, n;
int nMinLog;
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;
}
}
memsys5Enter();
nMinLog = memsys5Log(mem5.szAtom);
for(i=0; i<=LOGMAX && i+nMinLog<32; i++){
for(n=0, j=mem5.aiFreelist[i]; j>=0; j = MEM5LINK(j)->next, n++){}
fprintf(out, "freelist items of size %d: %d\n", mem5.szAtom << i, n);
}
fprintf(out, "mem5.nAlloc = %llu\n", mem5.nAlloc);
fprintf(out, "mem5.totalAlloc = %llu\n", mem5.totalAlloc);
fprintf(out, "mem5.totalExcess = %llu\n", mem5.totalExcess);
fprintf(out, "mem5.currentOut = %u\n", mem5.currentOut);
fprintf(out, "mem5.currentCount = %u\n", mem5.currentCount);
fprintf(out, "mem5.maxOut = %u\n", mem5.maxOut);
fprintf(out, "mem5.maxCount = %u\n", mem5.maxCount);
fprintf(out, "mem5.maxRequest = %u\n", mem5.maxRequest);
memsys5Leave();
if( out==stdout ){
fflush(stdout);
}else{
fclose(out);
}
}
#endif
/*
** This routine is the only routine in this file with external
** linkage. It returns a pointer to a static sqlite3_mem_methods
** struct populated with the memsys5 methods.
*/
const sqlite3_mem_methods *sqlite3MemGetMemsys5(void){
static const sqlite3_mem_methods memsys5Methods = {
memsys5Malloc,
memsys5Free,
memsys5Realloc,
memsys5Size,
memsys5Roundup,
memsys5Init,
memsys5Shutdown,
0
};
return &memsys5Methods;
}
#endif /* SQLITE_ENABLE_MEMSYS5 */