什么情况下会调用到session_destroy()

<code>; Defines the probability that the 'garbage collection' process is started
; on every session initialization. The probability is calculated by using
; gc_probability/gc_divisor. Where session.gc_probability is the numerator
; and gc_divisor is the denominator in the equation. Setting this value to 1
; when the session.gc_divisor value is 100 will give you approximately a 1% 
; chance the gc will run on any give request.
; Default Value: 1
; Development Value: 1
; Production Value: 1
; http://php.net/session.gc-probability
session.gc_probability = 1

; Defines the probability that the 'garbage collection' process is started 
; on every session initialization. The probability is calculated by using 
; the following equation: gc_probability/gc_divisor. Where session.gc_probability 
; is the numerator and session.gc_divisor is the denominator in the equation. 
; Setting this value to 1 when the session.gc_divisor value is 100 will give you 
; approximately a 1% chance the gc will run on any give request. Increasing this 
; value to 1000 will give you a 0.1% chance the gc will run on any give request. 
; For high volume production servers, this is a more efficient approach.
; Default Value: 100
; Development Value: 1000
; Production Value: 1000
; http://php.net/session.gc-divisor
session.gc_divisor = 1000

; After this number of seconds, stored data will be seen as 'garbage' and
; cleaned up by the garbage collection process.
; http://php.net/session.gc-maxlifetime
session.gc_maxlifetime = 1440
</code>

<code>session.gc_probability = 1
session.gc_divisor = 1000
</code>