PidControl.php

<?php
    namespace PidControl;

    class PidControl {
        protected $maxRunSec;
        protected $pidFile;

        function __construct($maxRunSec, $pidFile = false) {
            $this->setMaxRunSec($maxRunSec);
            if($pidFile === false) {
                $this->setPidFile(__FILE__ . '.pid');
            } else {
                $this->setPidFile($pidFile);
            }
        }

        /*
         * Use symlinking/atomic operations to prevent rare race conditions
         */
        public function writePid() {
            if(is_dir(dirname($this->getPidFile())) && is_writable(dirname($this->getPidFile()))) {
                return file_put_contents($this->getPidFile(), time() . ';' . getmypid());
            } else {
                throw new \Exception('PID File Not Writable: ' . $this->getPidFile());
            }
        }

        public function cleanupPid() {
            unlink($this->getPidFile());
        }

        public function start() {
            if(!is_file($this->getPidFile())) {
                $this->writePid();
                return true;
            } else {
                $pidData = file_get_contents($this->getPidFile());
                $pidPieces = explode(';', $pidData);

                if(!empty($pidData) && count($pidPieces) === 2) {
                    list($time, $existingPid) = $pidPieces;
                    if(is_dir("/proc/" . $existingPid)) {
                        throw new \Exception("PID File and /proc both say process id $existingPid is still running.  "
                            . "PID file indicates it has been running since " . date('r', $time));
                    } else {
                        if(($time + $this->getMaxRunSec()) < time()) {
                            $this->writePid();
                            trigger_error("PID file exists but seems to be stale, bravely proceeding and updating PID "
                                . "file.", E_USER_WARNING);
                            return true;
                        } else {
                            throw new \Exception("PID file exists, the PID no longer exists but I have not exceeded my "
                                . "timeout of " . $this->getMaxRunSec() . " seconds.");
                        }
                    }
                } else {
                    throw new \Exception("PID file exists but isn't the proper format, I don't know what to do!");
                }
            }
            return false;
        }

        public function end() {
            $this->cleanupPid();
        }

        public function setMaxRunSec($secs) {
            $this->maxRunSec = $secs;
        }

        public function getMaxRunSec() {
            return $this->maxRunSec;
        }

        public function setPidFile($file) {
            $this->pidFile = $file;
        }

        public function getPidFile() {
            return $this->pidFile;
        }
    }

    // EXAMPLE USAGE:
    $pidControl = new PidControl(3600);
    try {
        $pidControl->start();
    } catch(Exception $e) {
        mail('[email protected]', "PID File Issue", $e->getMessage());
    }

    // CODE CODE

    $pidControl->end();