Question

Is it possible in PHP to unregister a function (or all functions) set up with register_shutdown_function()?

Answer 1

I do not believe you can. The only way to unregister a callback function is to wrap it in some sort of class that only actually calls it based on certain conditions. Like this handy function wrapper:

class UnregisterableCallback{

    // Store the Callback for Later
    private $callback;

    // Check if the argument is callable, if so store it
    public function __construct($callback)
    {
        if(is_callable($callback))
        {
            $this->callback = $callback;
        }
        else
        {
            throw new InvalidArgumentException("Not a Callback");
        }
    }

    // Check if the argument has been unregistered, if not call it
    public function call()
    {
        if($this->callback == false)
            return false;

        $callback = $this->callback;
        $callback(); // weird PHP bug
    }

    // Unregister the callback
    public function unregister()
    {
        $this->callback = false;
    }
}

Basic usage:

$callback = new UnregisterableCallback(array($object, "myFunc"));

register_shutdown_function(array($callback, "call"));

To unregister

$callback->unregister();

Now, when called, it will return false and not call your callback function. There might be a few ways to streamline this process, but it works.

One such way of streamlining it would be to put the actual registration of the callback into a method of the callback function, so the outside world does not have to have knowledge that the method you have to pass to register_shutdown_function is “call”.