Memory leak in Fiber when calling __construct()

[TimWolla]

Description

When running the following code:

<?php

$fiber = new Fiber(function (): void {
   $value = Fiber::suspend('fiber');
   echo "Value used to resume fiber: ", $value, PHP_EOL;
});

$value = $fiber->start();

echo "Value from fiber suspending: ", $value, PHP_EOL;

$fiber->__construct(function (): void {
	echo "Bar";
	$value = Fiber::suspend('new');
	echo "Changed: ", $value, PHP_EOL;
});

$fiber->resume('test');

PHP will report a memory leak ("Total 1 memory leaks detected"):

==272678== Memcheck, a memory error detector
==272678== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==272678== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==272678== Command: sapi/cli/php test2.php
==272678== 
Value from fiber suspending: fiber
Value used to resume fiber: test
[Wed Apr 13 20:21:13 2022]  Script:  'php-src/test2.php'
php-src/Zend/zend_closures.c(505) :  Freeing 0x000000000506a480 (328 bytes), script=php-src/test2.php
=== Total 1 memory leaks detected ===
==272678== 
==272678== HEAP SUMMARY:
==272678==     in use at exit: 0 bytes in 0 blocks
==272678==   total heap usage: 14,370 allocs, 14,370 frees, 2,140,328 bytes allocated
==272678== 
==272678== All heap blocks were freed -- no leaks are possible
==272678== 
==272678== For lists of detected and suppressed errors, rerun with: -s
==272678== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

PHP Version

PHP 8.2.0-dev (commit 8233e06)

Operating System

Ubuntu 20.04

[cmb69]

Apparently the issue is:

php-src/Zend/zend_fibers.c

Lines 653 to 654 in ec0771c

	// Keep a reference to closures or callable objects while the fiber is running.
	Z_TRY_ADDREF(fiber->fci.function_name);

If fiber->fci is changed, the old fiber->fci.function_name would need to be deref'ed.

Regarding the leak checking in general: if you run with valgrind, always set USE_ZEND_ALLOC=0; otherwise valgrind will not detect any leaks, and the leak detection by the ZendMM isn't that helpful in finding where the leak occurred.

[trowski]

The reference to the running fiber function should not be removed while the fiber is running.

A subsequent call to the constructor should throw or do nothing. My vote would be throw.

[trowski]

Closed via #9098.