Made the code more robust.

Extended functionality with helper functions.

bin/app.php

@@ -3,33 +3,42 @@
 
 require_once __DIR__ . '/../vendor/autoload.php';
 
+use function Joop\Asynchronous\async;
+use Joop\Asynchronous\Promise;
+
+/**
+ * @param Promise[] $promises
+ */
+function awaitPromises(array &$promises)
+{
+	foreach ($promises as $index => $promise) {
+		if ($promise->isResolved()) {
+			unset($promises[$index]);
+
+			if (!$promise->isEmpty() && !$promise->isError())
+				print($promise->getValue() . PHP_EOL);
+		}
+	}
+}
+
+
+/*
+ * Example of asynchronous processing in PHP
+ */
 
-// Create a function we want to run asynchronously
 $process = function ($i) {
-	$delayMicroseconds = (10 - $i) * 1000000;
+	$delayMicroseconds = (5 - $i) * 1000000;
 	usleep($delayMicroseconds);
 
-	return getmypid();
+	return sprintf(
+		'PID %-5d slept for %.1f seconds',
+		getmypid(), $delayMicroseconds / 1000000
+	);
 };
 
-
-// Execute the functions asynchronously - each returning a Promise
 $promises = [];
-foreach (range(0, 10) as $i)
-	$promises[] = Asynchronous::run($process, $i);
-
-
-// Wait for all promises to resolve
-while (count($promises) > 0) {
-	foreach ($promises as $index => $promise) {
-		if ($promise->isResolved() && !$promise->isEmpty()) {
-			print("Response retrieved: " . $promise->getValue() . PHP_EOL);
-			unset($promises[$index]);
-		}
-	}
-}
-
-
-exit(0);
-
+foreach (range(0, 5) as $i)
+	$promises[] = async($process, $i);
 
+while (count($promises) > 0)
+	awaitPromises($promises);

bin/example/arrays.php

@@ -0,0 +1,15 @@
+#!/usr/bin/php
+<?php
+
+use function Joop\Asynchronous\async;
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+
+$promise = async(function () {
+	sleep(1);
+
+	return range(random_int(0, 10), random_int(20, 60));
+});
+
+$array = $promise->resolve()->getValue();
+var_dump($array);

bin/example/objects.php

@@ -0,0 +1,37 @@
+#!/usr/bin/php
+<?php
+
+use function Joop\Asynchronous\async;
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+
+
+// Example class
+class Sample
+{
+	private $data;
+
+	public function __construct()
+	{
+		$this->data = [1, 2, 3];
+	}
+
+	public function getData()
+	{
+		return $this->data;
+	}
+}
+
+// Create the process
+$promise = async(function () {
+	sleep(2);
+
+	return new Sample();
+});
+
+// We can do some other stuff here while the process is running
+
+// Resolve the promise
+/** @var Sample $sample */
+$sample = $promise->resolve()->getValue();
+var_dump($sample->getData());

bin/example/sample.php

@@ -0,0 +1,14 @@
+#!/usr/bin/php
+<?php
+
+use function Joop\Asynchronous\async;
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+
+$process = function ($number) {
+	sleep($number);
+	return $number;
+};
+
+async($process, 2);
+// Do stuff...

composer.json

@@ -7,13 +7,13 @@
         }
     ],
     "autoload": {
-        "psr-0": {
-            "": ["src"]
+        "files": ["src/functions.php"],
+        "psr-4": {
+            "Joop\\Asynchronous\\": ["src"]
         }
     },
     "require": {
         "ext-pcntl": "*",
-        "ext-curl": "*",
         "ext-sysvshm": "*"
     }
 }

src/Asynchronous.php

@@ -1,19 +1,23 @@
 <?php
 
+namespace Joop\Asynchronous;
 
 /**
  * Class Asynchronous
+ * Responsible for management of child processes and shared memory.
  */
 class Asynchronous
 {
-
+	/** @var Asynchronous|null */
 	private static $instance;
 
+	/** @var int */
+	private static $key = 0;
+
+
 	/** @var bool */
 	private $isChild = false;
 
-	private static $key = 0;
-
 	/** @var int[] */
 	private $children = [];
 
@@ -23,41 +27,6 @@ class Asynchronous
 	/** @var int */
 	private $shmKey;
 
-	/** @var string */
-	private $tempFile;
-
-	/**
-	 * Asynchronous constructor.
-	 */
-	private function __construct()
-	{
-		$this->tempFile = tempnam(__DIR__ . '/../temp', 'PHP');
-		$this->shmKey = ftok($this->tempFile, 'a');
-		Promise::_setShmKey($this->shmKey);
-		$this->attach();
-	}
-
-	/**
-	 * @return $this
-	 */
-	private function attach()
-	{
-		$this->shm = shm_attach($this->shmKey);
-
-		return $this;
-	}
-
-	/**
-	 * @return Asynchronous
-	 */
-	private static function getInstance()
-	{
-		if (is_null(self::$instance))
-			self::$instance = new static();
-
-		return self::$instance;
-	}
-
 
 	/**
 	 * @param callable $function
@@ -67,41 +36,142 @@ class Asynchronous
 	public static function run(callable $function, ...$parameters)
 	{
 		$instance = self::getInstance();
+		$key = self::generatePromiseKey();
 		$pid = pcntl_fork();
 
-		if ($pid === false)
+		/*
+		 * The fork failed. Instead of returning a promise, we return null.
+		 */
+		if ($pid == -1)
 			return null;
 
-		$key = self::generatePromiseKey();
-
+		/*
+		 * Parent process. We keep track of the PID of the child process
+		 * in order for us to read out it's status later on.
+		 * A Promise instance is returned that corresponds to the key in
+		 * memory to which the child process will write sometime.
+		 */
 		if ($pid > 0) {
 			$instance->children[] = $pid;
 
 			return new Promise($key);
 		}
 
+		/*
+		 * Child process. Mark the (copied) instance of this class as a child
+		 * to prevent unneeded shutdown handler execution.
+		 * Reattach to the shared memory block (the $shm member variable is a
+		 * resource since PHP > 5.3 and is thus not shared with the child)
+		 * and execute the function.
+		 * On a successful execution, write the result to the shared memory
+		 * block to which the parent is attached.
+		 * On failure, write a default response to the block in order for
+		 * the Promise to be able to resolve.
+		 */
 		$instance->isChild = true;
-		$instance->attach();
+		$instance->attachShm();
 		try {
-			$response = call_user_func($function, ...$parameters);
+			$response = call_user_func_array($function, $parameters);
 			shm_put_var($instance->shm, $key, $response ?? Promise::RESPONSE_NONE);
 			exit(0);
-		} catch (Throwable $throwable) {
+		} catch (\Throwable $throwable) {
+			shm_put_var($instance->shm, $key, Promise::RESPONSE_ERROR);
 			exit(1);
 		}
-
-
 	}
 
+	/**
+	 *
+	 */
+	public static function cleanup()
+	{
+		/*
+		 * Iterate over all child process PIDs and check
+		 * if one or more of them has stopped.
+		 */
+		$instance = self::getInstance();
+		foreach ($instance->children as $index => $pid) {
+			$response = pcntl_waitpid($pid, $status, WNOHANG);
+			if ($response === $pid)
+				unset($instance->children[$index]);
+		}
+	}
+
+	/**
+	 * @return int
+	 */
+	public static function childCount()
+	{
+		return count(self::getInstance()->children);
+	}
+
+
+
+	/*
+	 * Private methods below
+	 */
+
+	/**
+	 * Asynchronous constructor.
+	 */
+	private function __construct()
+	{
+		/*
+		 * Use the filename as an identifier to create the
+		 * System V IPC key.
+		 */
+		$this->shmKey = ftok(__FILE__, 't');
+		Promise::__setShmKey($this->shmKey);
+		$this->attachShm();
+	}
+
+
+	/**
+	 * @return $this
+	 */
+	private function attachShm()
+	{
+		$this->shm = shm_attach($this->shmKey);
+
+		return $this;
+	}
+
+
+	/**
+	 * @return Asynchronous
+	 */
+	private static function getInstance()
+	{
+		if (is_null(self::$instance)) {
+			/*
+			 * This is executed once during runtime;
+			 * when a functionality from this class
+			 * is used for the first time.
+			 */
+			self::$instance = new static();
+			self::registerHandlers();
+		}
+
+		return self::$instance;
+	}
+
+
 	/**
 	 * @return int
 	 */
 	private static function generatePromiseKey()
 	{
+		/*
+		 * Get the current key.
+		 */
 		$promiseKey = self::$key;
-		self::$key++;
-		if (self::$key > 9999999)
-			self::$key = 0;
+
+		/*
+		 * Reset the key to 0 if the upper bound of
+		 * 9.999.999 is reached (Windows limit for
+		 * shm keys).
+		 */
+		self::$key = (++self::$key > 9999999) ? 0 : self::$key;
 
 		return $promiseKey;
 	}
@@ -110,18 +180,48 @@ class Asynchronous
 	/**
 	 *
 	 */
-	public function __destruct()
+	private static function registerHandlers()
 	{
-		if ($this->isChild)
+		$instance = self::getInstance();
+
+		/*
+		 * The shutdown handler
+		 */
+		$handler = function () use (&$instance) {
+			/*
+			 * A child process has no business here.
+			 */
+			if ($instance->isChild)
 				return;
 
-		while (count($this->children) > 0) {
+			/*
+			 * Wait for all children to finish to
+			 * ensure that all writing to the shared
+			 * memory block is finished.
+			 */
+			while (count($instance->children) > 0) {
 				pcntl_wait($status);
-			array_shift($this->children);
+				array_shift($instance->children);
 			}
-		shm_remove($this->shm);
-		shm_detach($this->shm);
-		unlink($this->tempFile);
+
+			/*
+			 * Ask the kernel to mark the shared memory
+			 * block for removal and detach from it to
+			 * actually allow for removal.
+			 */
+			if (is_resource($instance->shm)) {
+				shm_remove($instance->shm);
+				shm_detach($instance->shm);
+			}
+		};
+
+		/*
+		 * Actually register the handler as shutdown
+		 * handler and signal handler for SIGINT, SIGTERM
+		 */
+		register_shutdown_function($handler);
+		foreach ([SIGINT, SIGTERM] as $SIGNAL)
+			pcntl_signal($SIGNAL, $handler);
 	}
 
 }

src/Promise.php

@@ -1,22 +1,46 @@
 <?php
 
+namespace Joop\Asynchronous;
 
 class Promise
 {
+	/*
+	 * Define some default responses that will make it easy for us
+	 * to check if the promise resulted in an error or if the promise
+	 * was fulfilled by a void function.
+	 * The '_' characters are arbitrary but ensure a higher entropy to
+	 * minimize the chances of result collision.
+	 */
 	public const RESPONSE_NONE = '__PROMISE_RESPONSE_NONE__';
-
-	private $shm;
-	private $key;
-	private $value;
+	public const RESPONSE_ERROR = '__PROMISE_RESPONSE_ERROR__';
 
 	/** @var int */
 	private static $shmKey;
 
-	public static function _setShmKey(int $shmKey)
+
+	/** @var resource */
+	private $shm;
+
+	/** @var int */
+	private $key;
+
+	/** @var mixed|null */
+	private $value;
+
+
+	/**
+	 * @param int $shmKey
+	 */
+	public static function __setShmKey(int $shmKey)
 	{
+		/*
+		 * Should be done only once: when the Asynchronous class
+		 * has created a key that will be used for IPC.
+		 */
 		self::$shmKey = $shmKey;
 	}
 
+
 	/**
 	 * Promise constructor.
 	 * @param int $key
@@ -28,45 +52,96 @@ class Promise
 		$this->shm = shm_attach(self::$shmKey);
 	}
 
+	/**
+	 * @return bool
+	 */
+	public function shmValid()
+	{
+		return is_resource($this->shm);
+	}
+
 	/**
 	 * @return bool
 	 */
 	public function isResolved()
 	{
+		if ($this->shmValid())
 			return shm_has_var($this->shm, $this->key);
+
+		return true;
 	}
 
+
 	/**
 	 * @return bool
 	 */
 	public function isEmpty()
 	{
-		return $this->getValue() === self::RESPONSE_NONE;
+		$value = $this->getValue();
+
+		return $value === self::RESPONSE_NONE || $value === null;
 	}
 
+
+	/**
+	 * @return bool
+	 */
+	public function isError()
+	{
+		return $this->getValue() === self::RESPONSE_ERROR;
+	}
+
+
 	/**
 	 * @return mixed|null
 	 */
 	public function getValue()
 	{
+		if ($this->shmValid())
 			return $this->isResolved() ? $this->resolve()->value : null;
+
+		$this->value = self::RESPONSE_ERROR;
+
+		return $this->value;
 	}
 
+
 	/**
 	 * @return $this
 	 */
 	public function resolve()
 	{
+		/*
+		 * Actually block execution until a value is written to
+		 * the expected location of this Promise.
+		 */
 		while (!$this->isResolved())
-			usleep(1000); // 1ms
+			usleep(1000);
 
+		if (is_null($this->value) && $this->shmValid())
 			$this->value = shm_get_var($this->shm, $this->key);
+
 		return $this;
 	}
 
+
+	/**
+	 *
+	 */
 	public function __destruct()
 	{
-		if (is_resource($this->shm))
+		/*
+		 * Clean up our mess - the variable that we stored in the
+		 * shared memory block - and detach from the block.
+		 * Note: this destructor is only called after the
+		 * garbage collector has noticed that there are no more
+		 * references to this Promise instance.
+		 */
+		if ($this->shmValid()) {
+			if (shm_has_var($this->shm, $this->key))
+				shm_remove_var($this->shm, $this->key);
+
 			shm_detach($this->shm);
 		}
 	}
+}

src/functions.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Joop\Asynchronous;
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+if (!function_exists('async_run')) {
+
+	/**
+	 * @param callable $function
+	 * @param mixed ...$parameters
+	 * @return Promise|null
+	 */
+	function async(callable $function, ...$parameters)
+	{
+		return Asynchronous::run($function, ...$parameters);
+	}
+}
+
+
+if (!function_exists('async_cleanup')) {
+	/**
+	 *
+	 */
+	function async_cleanup()
+	{
+		Asynchronous::cleanup();
+	}
+}