Bug #62452 [Com]: Variable Aliasing does not work in Closure

Edit report at https://bugs.php.net/bug.php?id=62452&edit=1 ID: 62452 Comment by: nikic@php.net Reported by: hanskrentel at yahoo dot de Summary: Variable Aliasing does not work in Closure Status: Re-Opened Type: Bug Package: Scripting Engine problem Operating System: Multiple PHP Version: Irrelevant Block user comment: N Private report: N New Comment: I just looked into this a bit but couldn't find a good way to fix it. The main issue is that the prototype hack is only done in ZEND_INIT_FCALL_BY_NAME and only for VARs. Doing the same for CVs (as in this case) would be easy, but it sadly does not work properly if the closure is also invoked using call_user_func or any other function using zend_call_function internally. zend_call_function does not back the closure into the prototype and due to the way it works I'm not sure how this could be added there. For zcf the get_closure object handler call is done within zend_is_callable_ex and the results are put into the passed function_call_cache then. But the fcc can be reused for multiple calls (or not be used at all), so I really don't know how to do this safely without causing leaks or double frees. Previous Comments: ------------------------------------------------------------------------ [2012-07-03 17:49:27] nikic@php.net @laruence: The closure can still exist even if it is not referenced by $f anymore. I didn't look into this yet, but the fix should be along the lines of adding a ref to the closure when it is called and removing it again when it finishes running. Actually, I remember seeing something in the code that backs up the function zval into op_array.prototype (disguised as a zend_function*) and dtors it in the leave_helper. But clearly that isn't enough yet. ------------------------------------------------------------------------ [2012-07-03 17:39:24] hanskrentel at yahoo dot de hi @laurence, thank's for taking the time to review it. If I write code like unset($this); it does not fatal error either (you can not destroy a object while you are calling it.). Also I don't want to destroy the closure, I just want to re-use that variable. Can't you just let the garbage collector do the dirty work? ------------------------------------------------------------------------ [2012-07-02 07:03:19] laruence@php.net you can not destroy a closure while you are calling it. when you override $f in $f, zend vm try to destroy the closure $f, since the refcout of it is 1. try following : $b = $f = function() use (&$f) { $f = function() {}; }; $f(); $f(); ------------------------------------------------------------------------ [2012-06-29 20:05:06] nikic@php.net Verified on master. ------------------------------------------------------------------------ [2012-06-29 19:53:22] hanskrentel at yahoo dot de Description: ------------ It's not possible to make use of variable aliasing in PHP when the alias is used within the use clause of a lambda function construct that is assigned to that variable (recursion). PHP denies to do what it is commanded with a Fatal error: Cannot destroy active lambda function. But the function is not destroyed. It's just not that the variable container contains the identifier of it. I'd like to change that, and I don't want to waste another variable name. Also I don't understand how I can actually destroy something I should not have any access to from PHP userland. Or if that is intended, please allow us to destroy the active lambda making the function return NULL and continue to execute. Test script: --------------- $f = function() use (&$f) { $f = function() {echo "hello"}; }; $f(); $f(); Expected result: ---------------- hello Actual result: -------------- Fatal error: Cannot destroy active lambda function ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=62452&edit=1