/*
** Change the size of an existing memory allocation
*/
static void *memsys3Realloc(sqlite4_env*pEnv, void *pPrior, int nBytes){
int nOld;
void *p;
if( pPrior==0 ){
return sqlite4_malloc(pEnv, nBytes);
}
if( nBytes<=0 ){
sqlite4_free(pEnv, 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;
}
//重新分配*pPrior指向的内存空间大小为n字节。
static void *memsys3Realloc(void *pPrior, int nBytes) {
int nOld;
void *p;
if( pPrior==0 ) { //原来的内存为0，则直接分配n字节
return sqlite3_malloc(nBytes);
}
if( nBytes<=0 ) {
sqlite3_free(pPrior); //释放从由sqlite3Malloc获得的内存空间
return 0;
}
nOld = memsys3Size(pPrior); //获取未完成分配的内存空间
if( nBytes<=nOld && nBytes>=nOld-128 ) {
return pPrior;
}
memsys3Enter();
p = memsys3MallocUnsafe(nBytes); //申请n字节的内存空间
if( p ) {
if( nOld<nBytes ) {
memcpy(p, pPrior, nOld);
} else {
memcpy(p, pPrior, nBytes);
}
memsys3FreeUnsafe(pPrior);
}
memsys3Leave();
return p;
}
/*
** Allocate nBytes of memory.
*/
static void *memsys3Malloc(int nBytes){
sqlite4_int64 *p;
assert( nBytes>0 ); /* malloc.c filters out 0 byte requests */
memsys3Enter();
p = memsys3MallocUnsafe(nBytes);
memsys3Leave();
return (void*)p;
}
//申请分配n字节的内存空间。
static void *memsys3Malloc(int nBytes) { //分配n字节的内存
sqlite3_int64 *p;
assert( nBytes>0 ); /* malloc.c filters out 0 byte requests *///请求字节为0则终止程序
memsys3Enter(); //获取共享锁
p = memsys3MallocUnsafe(nBytes); //分配内存
memsys3Leave(); //释放锁
return (void*)p; //返回空指针
}