sigHandlingDemo.php

<?php

/**
 * This is small demonstration of PHPs signal handling behavior.
 *
 * Both methods will fork children using pcntl_fork and output whether or not forked parent/child were created inside
 * of the registered sigHandler function, if it's the child or parent, and their respective PIDs.
 *
 * If you run spawnChildInsideHandler and attempt to send a SIGTERM (15) to either of the two processes
 * you will receive no response. To exit you will have to force kill with SIGKILL (9)
 *
 * If you run spawnChildOutsideHandler and attempt to send a SIGTERM (15) to either of the two processes you should see
 * output from the sigHandler function.
 *
 * The question to be answered is if this is intended behavior that isn't documented or a bug.
 */
spawnChildInsideHandler();
//spawnChildOutsideOfHandler();

function spawnChildOutsideOfHandler() {

	pcntl_async_signals(true);

	pcntl_signal(SIGTERM, "sigHandler", false);

	$pid = pcntl_fork();

	// child process
	if ($pid === 0) {

		echo "[Forked Without Signal] [CHILD] PID = " . getmypid() . PHP_EOL;
		wait();

	} // parent process
	elseif ($pid) {

		echo "[Forked Without Signal] [PARENT] PID = " . getmypid() . PHP_EOL;
		wait();
	}

}

function spawnChildInsideHandler() {

	pcntl_async_signals(true);

	pcntl_signal(SIGTERM, "sigHandler", false);
	pcntl_signal(SIGHUP, "sigHandler", false);

	posix_kill(getmypid(), SIGHUP);
}

function sigHandler($sigNum)
{
	$mypid = getmypid();

	if ($sigNum === SIGHUP) {

		echo "[{$mypid}] Received SIGHUP, forking off children\n";

		$pid = pcntl_fork();

		// child process
		if ($pid === 0) {

			echo "[Forked inside handler] [CHILD] PID = " . getmypid() . PHP_EOL;
			wait();

		} // parent process
		elseif ($pid) {

			echo "[Forked inside handler] [PARENT] PID = " . getmypid() . PHP_EOL;
			wait();
		}
	}

	echo "[{$mypid}] Received signal {$sigNum}\n";
}

function wait() {

	while (true) {
		sleep(1);
	}
}