PHP garbage collection mechanism

When assigning a value to a variable, PHP allocates a zval to store the value, while the ZVAL structure does not have a variable name.

After 5.3, the release improved the garbage collection mechanism
If you find that the refcount in a zval container is increasing, the description is not garbage
If you find that the refcount in a zval container is decreasing, if it is reduced to 0, it is directly garbage collected
If a refcount in a zval container is found to be reduced, and not reduced to 0,php, the value will be placed in the buffer, as suspected objects that may be garbage
When the buffer reaches a critical value, PHP automatically calls a method to iterate through each value, and if it finds garbage, clean it up.

PHP garbage collection mechanism