Handling of three connection states in php

Inside PHP, the system maintains the connection status, and its status has three possible situations:

0 - NORMAL (normal)

1 - ABORTED (abnormal exit)

2 - TIMEOUT (timeout)

When the PHP script is normal The connection is valid when running in NORMAL state. When the remote client disconnects, the ABORTED status flag will be turned on. Interruption of the remote client connection is usually caused by the user clicking the STOP button. When the connection time exceeds PHP's time limit, the TIMEOUT status flag will be turned on.

You can decide whether the script needs to exit when the client disconnects. Sometimes it is convenient to have a script run completely, even if no remote browser accepts the script's output. The default is for the script to exit when the remote client connection is lost. This process can be controlled by ignore_user_abort in php.ini or by the corresponding "php_value ignore_user_abort" and ignore_user_abort() functions in the httpd.conf setting. If PHP is not told to ignore user interruptions, the script will be interrupted unless a shutdown trigger function is set via register_shutdown_function(). Through this close trigger function, when the remote user clicks the STOP button and the script tries to output data again, PHP will detect that the connection has been interrupted and call the close trigger function.

Scripts may also be interrupted by the built-in script timer. The default timeout limit is 30 seconds. This value can be changed by setting the max_execution_time of php.ini or the corresponding "php_value max_execution_time" parameter in the httpd.conf setting or the set_time_limit() function. When the counter times out, the script will exit similar to the above connection interruption situation, and the previously registered shutdown trigger function will also be executed at this time. In the shutdown trigger function, you can check whether the timeout caused the shutdown trigger function to be called by calling the connection_status() function. If a timeout results in a call to the shutdown triggering function, the function will return 2.

One thing to note is that the ABORTED and TIMEOUT states can be valid at the same time. This is possible when telling PHP to ignore user exit actions. PHP will still notice that the user has disconnected but the script is still running. If the running time limit is reached, the script will be exited and the set shutdown trigger function will also be executed. At this point you will find that the function connection_status() returns 3.