php的过期的session文件是怎么回收的

; Define the probability that the 'garbage collection' process is started
; on every session initialization.
; The probability is calculated by using gc_probability/gc_divisor,
; e.g. 1/100 means there is a 1% chance that the GC process starts
; on each request.

session.gc_probability = 1
session.gc_divisor     = 100

; After this number of seconds, stored data will be seen as 'garbage' and
; cleaned up by the garbage collection process.
session.gc_maxlifetime = 1440

Cleans up expired sessions. Called randomly by PHP internally when a sessio starts or when session_start() is invoked. The frequency this is called is based on the session.gc_divisor and session.gc_probability configuration directives.

This method wraps the internal PHP save handler defined in the session.save_handler ini setting that was set before this handler was set by session_set_save_handler().

If this class is extended by inheritiance, calling the parent gc method will invoke the wrapper for this method and therefor invoke the associated internal callback. This allows this method to be overidden and or intercepted and filtered.

For more information on what this method is expected to do, please refer to the documentation at SessionHandlerInterface::gc().