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Filename : ForkingLoop.php
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<?php

/*
 * This file is part of Psy Shell.
 *
 * (c) 2012-2017 Justin Hileman
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Psy\ExecutionLoop;

use Psy\Context;
use Psy\Shell;

/**
 * A forking version of the Psy Shell execution loop.
 *
 * This version is preferred, as it won't die prematurely if user input includes
 * a fatal error, such as redeclaring a class or function.
 */
class ForkingLoop extends Loop
{
    private $savegame;

    /**
     * Run the execution loop.
     *
     * Forks into a master and a loop process. The loop process will handle the
     * evaluation of all instructions, then return its state via a socket upon
     * completion.
     *
     * @param Shell $shell
     */
    public function run(Shell $shell)
    {
        list($up, $down) = stream_socket_pair(STREAM_PF_UNIX, STREAM_SOCK_STREAM, STREAM_IPPROTO_IP);

        if (!$up) {
            throw new \RuntimeException('Unable to create socket pair.');
        }

        $pid = pcntl_fork();
        if ($pid < 0) {
            throw new \RuntimeException('Unable to start execution loop.');
        } elseif ($pid > 0) {
            // This is the main thread. We'll just wait for a while.

            // We won't be needing this one.
            fclose($up);

            // Wait for a return value from the loop process.
            $read   = array($down);
            $write  = null;
            $except = null;
            if (stream_select($read, $write, $except, null) === false) {
                throw new \RuntimeException('Error waiting for execution loop.');
            }

            $content = stream_get_contents($down);
            fclose($down);

            if ($content) {
                $shell->setScopeVariables(@unserialize($content));
            }

            return;
        }

        // This is the child process. It's going to do all the work.
        if (function_exists('setproctitle')) {
            setproctitle('psysh (loop)');
        }

        // We won't be needing this one.
        fclose($down);

        // Let's do some processing.
        parent::run($shell);

        // Send the scope variables back up to the main thread
        fwrite($up, $this->serializeReturn($shell->getScopeVariables(false)));
        fclose($up);

        posix_kill(posix_getpid(), SIGKILL);
    }

    /**
     * Create a savegame at the start of each loop iteration.
     */
    public function beforeLoop()
    {
        $this->createSavegame();
    }

    /**
     * Clean up old savegames at the end of each loop iteration.
     */
    public function afterLoop()
    {
        // if there's an old savegame hanging around, let's kill it.
        if (isset($this->savegame)) {
            posix_kill($this->savegame, SIGKILL);
            pcntl_signal_dispatch();
        }
    }

    /**
     * Create a savegame fork.
     *
     * The savegame contains the current execution state, and can be resumed in
     * the event that the worker dies unexpectedly (for example, by encountering
     * a PHP fatal error).
     */
    private function createSavegame()
    {
        // the current process will become the savegame
        $this->savegame = posix_getpid();

        $pid = pcntl_fork();
        if ($pid < 0) {
            throw new \RuntimeException('Unable to create savegame fork.');
        } elseif ($pid > 0) {
            // we're the savegame now... let's wait and see what happens
            pcntl_waitpid($pid, $status);

            // worker exited cleanly, let's bail
            if (!pcntl_wexitstatus($status)) {
                posix_kill(posix_getpid(), SIGKILL);
            }

            // worker didn't exit cleanly, we'll need to have another go
            $this->createSavegame();
        }
    }

    /**
     * Serialize all serializable return values.
     *
     * A naïve serialization will run into issues if there is a Closure or
     * SimpleXMLElement (among other things) in scope when exiting the execution
     * loop. We'll just ignore these unserializable classes, and serialize what
     * we can.
     *
     * @param array $return
     *
     * @return string
     */
    private function serializeReturn(array $return)
    {
        $serializable = array();

        foreach ($return as $key => $value) {
            // No need to return magic variables
            if (Context::isSpecialVariableName($key)) {
                continue;
            }

            // Resources and Closures don't error, but they don't serialize well either.
            if (is_resource($value) || $value instanceof \Closure) {
                continue;
            }

            try {
                @serialize($value);
                $serializable[$key] = $value;
            } catch (\Exception $e) {
                // we'll just ignore this one...
            } catch (\Throwable $e) {
                // and this one too...
            }
        }

        return @serialize($serializable);
    }
}