Before php5.3 versions, variable recovery mechanisms php simply processes (when refcount = 0, reclaims memory) by counting, but this will be a problem
$a=array("str");
$a[]=&$a;
unset($a);
Before performing unset, $ a refcount of 2, after performing unset, $ a is refcout 1, because it is not equal to 0, the memory can not be recovered, i.e. waste, of course, after a php script completes the assigned memory will all be recycled, but now used in addition to the php script, more places for writing a daemon service (of course I do not recommend), may take up to a month, two months before the end of the script, such as the above procedures during this period It will produce memory overflow
Note: unset and can not release memory, you need to look at the zval refcount is 0
php5.3 later by the GC garbage collection
When allocating zval, to zval_gc_info units
#define ALLOC_ZVAL(z) \
do { \
(z) = (zval*)emalloc(sizeof(zval_gc_info)); \
GC_ZVAL_INIT(z); \
} while (0)
typedef struct _zval_gc_info {
zval z;
union {
gc_root_buffer *buffered;
struct _zval_gc_info *next;
} u;
} zval_gc_info;
#define FREE_ZVAL(z) \
do { \
GC_REMOVE_ZVAL_FROM_BUFFER(z); \
efree(z); \
} while (0)
typedef struct _gc_root_buffer {
struct _gc_root_buffer *prev; /* double-linked list */
struct _gc_root_buffer *next;
zend_object_handle handle; /* must be 0 for zval */
union {
zval *pz;
zend_object_handlers *handlers;
} u;
} gc_root_buffer;
Php when the GC recovery mechanism starts, it allocates space of 10,000 gc_root_buffer
ZEND_API void gc_init(TSRMLS_D)
{
if (GC_G(buf) == NULL && GC_G(gc_enabled)) {
GC_G(buf) = (gc_root_buffer*) malloc(sizeof(gc_root_buffer) * GC_ROOT_BUFFER_MAX_ENTRIES);
GC_G(last_unused) = &GC_G(buf)[GC_ROOT_BUFFER_MAX_ENTRIES];
gc_reset(TSRMLS_C);
}
}
When the unset ($ a), detailed here after a key is found in the zval active_systom_table, performs its value destructor, which was the zval refcount-1, 1 if the value is 0 after subtraction, immediate release may be described memory, if it is greater than 0, in place gc_root_buffer
ZEND_API void _zval_ptr_dtor(zval **zval_ptr ZEND_FILE_LINE_DC) /* {{{ */
{
Z_DELREF_PP(zval_ptr);
if (Z_REFCOUNT_PP(zval_ptr) == 0) {
TSRMLS_FETCH();
if (*zval_ptr != &EG(uninitialized_zval)) {
GC_REMOVE_ZVAL_FROM_BUFFER(*zval_ptr);
zval_dtor(*zval_ptr);
efree_rel(*zval_ptr);
}
} else {
TSRMLS_FETCH();
if (Z_REFCOUNT_PP(zval_ptr) == 1) {
Z_UNSET_ISREF_PP(zval_ptr);
}
GC_ZVAL_CHECK_POSSIBLE_ROOT(*zval_ptr);
}
}
#define GC_ZVAL_CHECK_POSSIBLE_ROOT(z) /
gc_zval_check_possible_root((z) TSRMLS_CC)
static zend_always_inline void gc_zval_check_possible_root(zval *z TSRMLS_DC)
{
if (z->type == IS_ARRAY || z->type == IS_OBJECT) {
gc_zval_possible_root(z TSRMLS_CC);
}
}
ZEND_API void gc_zval_possible_root(zval *zv TSRMLS_DC)
{
if (UNEXPECTED(GC_G(free_list) != NULL &&
GC_ZVAL_ADDRESS(zv) != NULL &&
GC_ZVAL_GET_COLOR(zv) == GC_BLACK) &&
(GC_ZVAL_ADDRESS(zv) < GC_G(buf) ||
GC_ZVAL_ADDRESS(zv) >= GC_G(last_unused))) {
/ * A Garbage of The IS GIVEN that the zval IS deleted by going to BE
* Currently running the GC * /
return;
}
IF (zv-> type == IS_OBJECT) {
GC_ZOBJ_CHECK_POSSIBLE_ROOT (ZV);
return;
}
GC_BENCH_INC (zval_possible_root); // zv gc_root_buffer If the last two are not purple, then processed
IF (GC_ZVAL_GET_COLOR (zv) = GC_PURPLE!) {
GC_ZVAL_SET_PURPLE (zv); // set purple IF {(GC_ZVAL_ADDRESS (zv)!)
gc_root_buffer * = newRoot GC_G ( unused);
IF (newRoot) {
GC_G (unused) = newRoot-> PREV;
!} the else IF (GC_G (first_unused) = GC_G (last_unused)) {
newRoot = GC_G(first_unused);
GC_G(first_unused)++;
} else {
if (!GC_G(gc_enabled)) {
GC_ZVAL_SET_BLACK(zv);
return;
}
zv->refcount__gc++;
gc_collect_cycles(TSRMLS_C);
zv->refcount__gc--;
newRoot = GC_G(unused);
if (!newRoot) {
return;
}
GC_ZVAL_SET_PURPLE(zv);
GC_G(unused) = newRoot->prev;
}
newRoot->next = GC_G(roots).next;
newRoot->prev = &GC_G(roots);
GC_G(roots).next->prev = newRoot;
GC_G(roots).next = newRoot;
GC_ZVAL_SET_ADDRESS(zv, newRoot); //将gc_root_buffer放到zval_gc_info结构体中
newRoot->handle = 0;
newRoot->u.pz = zv;
GC_BENCH_INC(zval_buffered);
GC_BENCH_INC(root_buf_length);
GC_BENCH_PEAK(root_buf_peak, root_buf_length);
}
}
}
The current zval into gc_root_bufer, each zval put only once, based on whether the color gc_root_buffer of zval_gc_info zval located in the purple
#define GC_ZVAL_GET_COLOR(v) \
GC_GET_COLOR(((zval_gc_info*)(v))->u.buffered)
#define GC_GET_COLOR(v) \
(((zend_uintptr_t)(v)) & GC_COLOR)
If it is purple, then to purple
#define GC_ZVAL_SET_PURPLE(v) \
GC_SET_PURPLE(((zval_gc_info*)(v))->u.buffered)
#define GC_SET_PURPLE(v) \
(v) = ((gc_root_buffer*)(((zend_uintptr_t)(v)) | GC_PURPLE))
Macro GC_ZVAL_SET_ADDRESS (zv, newRoot); gc_root_buffer newRoot used to place the corresponding position zv
#define GC_COLOR 0x03
#define GC_BLACK 0x00
#define GC_WHITE 0x01
#define GC_GREY 0x02
#define GC_PURPLE 0x03
#define GC_ZVAL_SET_ADDRESS(v, a) \
GC_SET_ADDRESS(((zval_gc_info*)(v))->u.buffered, (a))
#define GC_SET_ADDRESS(v, a) \
(v) = ((gc_root_buffer*)((((zend_uintptr_t)(v)) & GC_COLOR) | ((zend_uintptr_t)(a))))
GC_ZVAL_SET_ADDRESS macro v forced into zval_gc_info first type, itself zval when allocating memory, is to zval_gc_info units, into the strong zval *, since only zval padding data structure, this need not gc_root_buffer * bufer like members
because zval_gc_val structure, the first member of the zval z, z, then the memory address is the address itself zval_gc_info
in PHP GC using colors to indicate the waste processing
pointer in both 32-bit machine or a 64-bit machine The last two are 0,
gc_collect_cycles waste disposal
ZEND_API int gc_collect_cycles(TSRMLS_D)
{
int count = 0;
if (GC_G(roots).next != &GC_G(roots)) {
zval_gc_info *p, *q, *orig_free_list, *orig_next_to_free;
if (GC_G(gc_active)) {
return 0;
}
GC_G(gc_runs)++;
GC_G(zval_to_free) = FREE_LIST_END;
GC_G(gc_active) = 1;
gc_mark_roots(TSRMLS_C);
gc_scan_roots(TSRMLS_C);
gc_collect_roots(TSRMLS_C);
orig_free_list = GC_G(free_list);
orig_next_to_free = GC_G(next_to_free);
p = GC_G(free_list) = GC_G(zval_to_free);
GC_G(zval_to_free) = NULL;
GC_G(gc_active) = 0;
/* First call destructors */
while (p != FREE_LIST_END) {
if (Z_TYPE(p->z) == IS_OBJECT) {
if (EG(objects_store).object_buckets &&
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].valid &&
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.refcount <= 0 &&
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.dtor &&
!EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].destructor_called) {
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].destructor_called = 1;
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.refcount++;
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.dtor(EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.object, Z_OBJ_HANDLE(p->z) TSRMLS_CC);
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.refcount--;
}
}
count++;
p = p->u.next;
}
/* Destroy zvals */
p = GC_G(free_list);
while (p != FREE_LIST_END) {
GC_G(next_to_free) = p->u.next;
if (Z_TYPE(p->z) == IS_OBJECT) {
if (EG(objects_store).object_buckets &&
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].valid &&
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.refcount <= 0) {
EG(objects_store).object_buckets[Z_OBJ_HANDLE(p->z)].bucket.obj.refcount = 1;
Z_TYPE(p->z) = IS_NULL;
zend_objects_store_del_ref_by_handle_ex(Z_OBJ_HANDLE(p->z), Z_OBJ_HT(p->z) TSRMLS_CC);
}
} else if (Z_TYPE(p->z) == IS_ARRAY) {
Z_TYPE(p->z) = IS_NULL;
zend_hash_destroy(Z_ARRVAL(p->z));
FREE_HASHTABLE(Z_ARRVAL(p->with));
} else {
zval_dtor(&p->z);
Z_TYPE(p->z) = IS_NULL;
}
p = GC_G(next_to_free);
}
/* Free zvals */
p = GC_G(free_list);
while (p != FREE_LIST_END) {
q = p->u.next;
FREE_ZVAL_EX(&p->z);
p = q;
}
GC_G(collected) += count;
GC_G(free_list) = orig_free_list;
GC_G(next_to_free) = orig_next_to_free;
}
return count;
}
gc_mark_roots (TSRMLS_C); spam lay color marker, traverse gc_root_buffer, which was changed to purple to gray u.pz traversing u.pz each element of the array zval,. 1-which the refcount,
gc_collect_roots traverse gc_root_buffer, if refcount = = 0 then set to white, expressed as spam, if refcount> 0, indicate someone may be using, set to black
static void gc_mark_roots(TSRMLS_D)
{
gc_root_buffer *current = GC_G(roots).next;
while (current != &GC_G(roots)) {
if (current->handle) {
if (EG(objects_store).object_buckets) {
//处理对象,暂时不用看
}
} else {
if (GC_ZVAL_GET_COLOR(current->u.pz) == GC_PURPLE) {
zval_mark_grey(current->u.pz TSRMLS_CC);
} else {
GC_ZVAL_SET_ADDRESS(current->u.pz, NULL);
GC_REMOVE_FROM_BUFFER(current);
}
}
current = current->next;
}
}
static void zval_mark_grey(zval *pz TSRMLS_DC)
{
Bucket *p;
tail_call:
if (GC_ZVAL_GET_COLOR(pz) != GC_GREY) {
p = NULL;
GC_BENCH_INC(zval_marked_grey);
GC_ZVAL_SET_COLOR(pz, GC_GREY);
if (Z_TYPE_P(pz) == IS_OBJECT && EG(objects_store).object_buckets) {
//对象的处理, 暂时不用管
} else if (Z_TYPE_P(pz) == IS_ARRAY) {
if (Z_ARRVAL_P(pz) == &EG(symbol_table)) {
GC_ZVAL_SET_BLACK(pz);
} else {
p = Z_ARRVAL_P(pz)->pListHead;
}
}
while (p != NULL) {
pz = *(zval**)p->pData;
if (Z_TYPE_P(pz) != IS_ARRAY || Z_ARRVAL_P(pz) != &EG(symbol_table)) {
pz->refcount__gc--;
}
if (p->pListNext == NULL) {
goto tail_call;
} else {
zval_mark_grey(pz TSRMLS_CC);
}
p = p->pListNext;
}
}
}
The second pass gc_root_buffer, zv if the color is gray, and refcount = 0, then set to white, when refcount> 0, is set to black (not spam)
static void gc_scan_roots(TSRMLS_D)
{
gc_root_buffer *current = GC_G(roots).next;
while (current != &GC_G(roots)) {
if (current->handle) {
zval z;
INIT_PZVAL(&z);
Z_OBJ_HANDLE(z) = current->handle;
Z_OBJ_HT(z) = current->u.handlers;
zobj_scan(&z TSRMLS_CC);
} else {
zval_scan(current->u.pz TSRMLS_CC);
}
current = current->next;
}
}
static int zval_scan(zval *pz TSRMLS_DC)
{
Bucket *p;
tail_call:
if (GC_ZVAL_GET_COLOR(pz) == GC_GREY) {
p = NULL;
if (pz->refcount__gc > 0) {
zval_scan_black(pz TSRMLS_CC);
} else {
GC_ZVAL_SET_COLOR(pz, GC_WHITE);
if (Z_TYPE_P(pz) == IS_OBJECT && EG(objects_store).object_buckets) {
//处理object
} else if (Z_TYPE_P(pz) == IS_ARRAY) {
if (Z_ARRVAL_P(pz) == &EG(symbol_table)) {
GC_ZVAL_SET_BLACK(pz);
} else {
p = Z_ARRVAL_P(pz)->pListHead;
}
}
}
while (p != NULL) {
if (p->pListNext == NULL) {
pz = *(zval**)p->pData;
goto tail_call;
} else {
zval_scan(*(zval**)p->pData TSRMLS_CC);
}
p = p->pListNext;
}
}
return 0;
}
Gc_root_buffer linked list traversal, the placement of a single color zv list is white data, full recovery
static void gc_collect_roots(TSRMLS_D)
{
gc_root_buffer *current = GC_G(roots).next;
while (current != &GC_G(roots)) {
if (current->handle) {
if (EG(objects_store).object_buckets) {
struct _store_object *obj = &EG(objects_store).object_buckets[current->handle].bucket.obj;
zval z;
GC_SET_ADDRESS(obj->buffered, NULL);
INIT_PZVAL(&z);
Z_OBJ_HANDLE(z) = current->handle;
Z_OBJ_HT(z) = current->u.handlers;
zobj_collect_white(&z TSRMLS_CC);
}
} else {
GC_ZVAL_SET_ADDRESS(current->u.pz, NULL);
zval_collect_white(current->u.pz TSRMLS_CC);
}
GC_REMOVE_FROM_BUFFER(current);
current = current->next;
}
}
static void zval_collect_white(zval *pz TSRMLS_DC)
{
Bucket *p;
tail_call:
if (((zval_gc_info*)(pz))->u.buffered == (gc_root_buffer*)GC_WHITE) {
p = NULL;
GC_ZVAL_SET_BLACK(pz);
if (Z_TYPE_P(pz) == IS_OBJECT && EG(objects_store).object_buckets) {
...
} else {
if (Z_TYPE_P(pz) == IS_ARRAY) {
p = Z_ARRVAL_P(pz)->pListHead;
}
}
/* restore refcount and put into list to free */
pz->refcount__gc++;
((zval_gc_info*)pz)->u.next = GC_G(zval_to_free);
GC_G(zval_to_free) = (zval_gc_info*)pz;
while (p != NULL) {
pz = *(zval**)p->pData;
if (Z_TYPE_P(pz) != IS_ARRAY || Z_ARRVAL_P(pz) != &EG(symbol_table)) {
pz->refcount__gc++;
}
if (p->pListNext == NULL) {
goto tail_call;
} else {
zval_collect_white(pz TSRMLS_CC);
}
p = p->pListNext;
}
}
}