`DefaultJobRunner` deadlocks on child processes that write large amounts of stderr output

[MauricioFauth]

Q	A
PHPUnit version	10.5.36
PHP version	8.3.12
Installation Method	Composer
OS	Debian testing with deb.sury.org repository

Summary

When there's a lot of errors triggered before running PHPUnit, for example when a installed package triggers a lot of deprecation messages when being auto loaded, and there's a test that runs in a separate process, PHPUnit will hang indefinitely.

Current behavior

The process blocks here when reading stdout:

$stdout = stream_get_contents($pipes[1]);

phpunit/src/Util/PHP/DefaultPhpProcess.php

Lines 115 to 125 in 0c843b0

	if (isset($pipes[1])) {
	$stdout = stream_get_contents($pipes[1]);
	fclose($pipes[1]);
	}
	if (isset($pipes[2])) {
	$stderr = stream_get_contents($pipes[2]);
	fclose($pipes[2]);
	}

Replacing both stream_get_contents calls (stdout and stderr) with this old code (without the timeout check) fixed the issue (removed by ccb3b24):

phpunit/src/Util/PHP/DefaultPhpProcess.php

Lines 125 to 182 in dc7281e

	unset($pipes[0]);
	while (true) {
	$r = $pipes;
	$w = null;
	$e = null;
	$n = @stream_select($r, $w, $e, $this->timeout);
	if ($n === false) {
	break;
	}
	if ($n === 0) {
	proc_terminate($process, 9);
	throw new PhpProcessException(
	sprintf(
	'Job execution aborted after %d seconds',
	$this->timeout,
	),
	);
	}
	if ($n > 0) {
	foreach ($r as $pipe) {
	$pipeOffset = 0;
	foreach ($pipes as $i => $origPipe) {
	if ($pipe === $origPipe) {
	$pipeOffset = $i;
	break;
	}
	}
	if (!$pipeOffset) {
	break;
	}
	$line = fread($pipe, 8192);
	if ($line === '' || $line === false) {
	fclose($pipes[$pipeOffset]);
	unset($pipes[$pipeOffset]);
	} elseif ($pipeOffset === 1) {
	$stdout .= $line;
	} else {
	$stderr .= $line;
	}
	}
	if (empty($pipes)) {
	break;
	}
	}
	}

How to reproduce

IssueTest.php:

use PHPUnit\Framework\Attributes\RunInSeparateProcess;
use PHPUnit\Framework\TestCase;

final class IssueTest extends TestCase
{
    #[RunInSeparateProcess]
    public function testOne(): void
    {
        $this->assertTrue(true);
    }
}

file_that_trigger_errors.php:

<?php
trigger_error("error 1");
trigger_error("error 2");
trigger_error("error 3");
// ...
trigger_error("error 9997");
trigger_error("error 9998");
trigger_error("error 9999");

php.ini:

error_reporting=-1
display_errors=1
display_startup_errors=1
memory_limit=-1
zend.assertions=1
assert.exception=1

composer.json:

    "autoload-dev": { "files": [ "file_that_trigger_errors.php" ] }

[staabm]

great report.

adding back async streams would also help in not blocking the phpunit main process while workers do their thing

[staabm]

I can reproduce in PHPUnit 11.5.x using

IssueTest5993.php

--TEST--
PHPUnit process is blocked when there's a lot of output and a test with separate process
--INI--
error_reporting=-1
display_errors=1
display_startup_errors=1
memory_limit=-1
zend.assertions=1
assert.exception=1
--SKIPIF--
<?php
for ($i = 0; $i < 390; $i++) {
    trigger_error("error $i");
}
?>
--FILE--
<?php

use PHPUnit\Framework\Attributes\RunInSeparateProcess;
use PHPUnit\Framework\TestCase;

final class IssueTest5993 extends TestCase
{
    #[RunInSeparateProcess]
    public function testOne(): void
    {
        $this->assertTrue(true);
    }
}

using one less trigger_error it does not reproduce for me

for ($i = 0; $i < 389; $i++) {
    trigger_error("error $i");
}

when dropping the #[RunInSeparateProcess] attribute it also no longer reproduces

[staabm]

Note to self: maybe our problem is similar to https://github.com/php/php-src/pull/16456/files