test-SA_RESTART-in-pcntl_signal.php

<?php

// This exitcode means the alarm handler of the parent process killed the child
define ('EXITCODE_PARENT_INTERVENED', 0); // MUST be 0

// This exitcode means the child achieved the second lock. That'd be weird.
define ('EXITCODE_LOCK_ACHIEVED', 1);

// This exitcode means the second lock got interrupted (and returned false).
define ('EXITCODE_LOCK_INTERRUPTED', 2);

// This exitcode means the alarm handler in the child got handled. We probably don't expect that to happen in the fixed case.
define ('EXITCODE_ALARM_HANDLED', 3);

function handleHungChildprocess($pid) {
	return function() use ($pid) {
		posix_kill($pid, SIGSTOP);
		//echo "[parent] Killing pid $pid\n";
	};
}

function runPcntlTest(bool $restartSyscalls, bool $wantAlarm) {
	$pid = pcntl_fork();

	if (!$pid) {
		// child process that will run the test
		pcntl_signal(
			SIGALRM,
			function() use ($wantAlarm) {
				if ($wantAlarm)
					exit(EXITCODE_ALARM_HANDLED);
			},
			$restartSyscalls
		);

		pcntl_alarm(1);

		//echo "[child] I am child #", getmypid(), "\n";
		touch('./lock.txt');
		$fp = fopen('lock.txt', 'r');
		flock($fp, LOCK_EX);

		$fp2 = fopen('lock.txt', 'r');
		$locked = flock($fp2, LOCK_EX);

		if ($locked === false) {
			exit(EXITCODE_LOCK_INTERRUPTED);
		}

		// we'll never actually get here
		exit(EXITCODE_LOCK_ACHIEVED);
	} else {
		//echo "[parent] running as #", getmypid(), "\n";
		// parent process;
		pcntl_signal(SIGALRM, handleHungChildprocess($pid), false);
		pcntl_alarm(2);

		pcntl_waitpid($pid, $status, WUNTRACED );

		$exitCode = pcntl_wexitstatus($status);

		//echo "[parent] Child returned code $exitCode\n";
		return $exitCode;
	}

	throw new Exception("Couldnt fork");
}

pcntl_async_signals(true);

$exitCodeMapping = [
	EXITCODE_LOCK_INTERRUPTED => 'EXITCODE_LOCK_INTERRUPTED',
	EXITCODE_ALARM_HANDLED   => 'EXITCODE_ALARM_HANDLED',
	EXITCODE_PARENT_INTERVENED => 'EXITCODE_PARENT_INTERVENED'
];

$scenarios = [
	'Without SA_RESTART, without alarm, interrupted flock fails' => [
		'restartSyscalls' => false,
		'wantAlarm'       => false,
		'expectedExitCode' => EXITCODE_LOCK_INTERRUPTED
	],

	'Without SA_RESTART, with alarm, signal handler gets called' => [
		'restartSyscalls' => false,
		'wantAlarm'       => true,
		'expectedExitCode' => EXITCODE_ALARM_HANDLED
	],

	'With SA_RESTART: interrupted flock fails to call signal handler and gets terminated' => [
		'restartSyscalls'  => true,
		'wantAlarm'        => true,
		'expectedExitCode' => EXITCODE_PARENT_INTERVENED
	]
];

foreach ($scenarios as $description => $arguments) {
	echo "Runnning '$description' .... ";
	$exitCode = runPcntlTest($arguments['restartSyscalls'], $arguments['wantAlarm']);

	echo $exitCode === $arguments['expectedExitCode'] ?
		"SUCCESS\n" :
		sprintf(
			"FAILED! Got exitcode %d (%s) instead of %d (%s)\n",
			$exitCode,
			$exitCodeMapping[$exitCode],
			$arguments['expectedExitCode'],
			$exitCodeMapping[$arguments['expectedExitCode']]
		);
}