What are the contents related to PHP garbage collection and memory management

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Guidelines for PHP garbage Collection and memory Management

This article will talk about garbage collection and memory management in the development of PHP.

Reference count

In PHP 5.2 and previous versions, PHP garbage collection used the reference counting algorithm.

Basic knowledge of reference counting

Basic knowledge of reference counting

The variables for php are stored in the "zval" variable container (data structure), and the "zval" attribute contains the following information:

The data type of the current variable

The value of the current variable

Is_ref Boolean type identification used to identify whether a variable is passed by a reference

The refcount identifier that points to the number of variables in the "zval" variable container (that is, the number of times this zval is referenced, note that the reference here does not refer to the reference passing value, note the distinction).

When a variable is assigned, a corresponding "zavl" variable container is generated.

View variable zval container information

To view the "zval" container information of a variable (that is, to view the is_ref and refcount of a variable), you can use the xdebug_debug_zval () function of the XDebug debugger.

Assuming that we have successfully installed the XDebug tool, we are ready to debug the variables.

View the zval information of ordinary variables

If our PHP statement simply assigns a variable, the is_ref identification value is 0 and the refcount value is 1; if this variable is assigned to another variable as a value, the refcount count of the zval variable container is increased; similarly, when the variable is destroyed (unset), the corresponding "refcount" minus 1.

Take a look at the following example: