CRON PHP Daemon

cron.php

#!/usr/bin/php
<?php
/**
 * Need to test code works on ©Win"virus"dow$
 *
 * Aim:
 * To run code within a cron task at a settable frequency above 1 per minute,
 *  but not overrun the minute or run again if already running, tasks should
 *  also complete at their own pace within the minute.
 *
 * Solution:
 *
 * Controlling state:
 *  Define the state by setting a variable as false, look for a pid file,
 *  if the pid file is found but the variable is not running, assume the script
 *  died prematurely, attempt to kill the process, write new pid to file.
 *
 * Code iteration frequency:
 *  Using a while loop watch the time() + 60 !> time() this makes it much
 *  simpler to define our sleep time and turns time back into a frequency rather
 *  then a calculation.
 *
 * Setup cron to run every minute (brakes if task breaks):
 *    * * * * * /usr/bin/php /home/lozza/cron.php
 * Setup cron to run at start but continue to run (restarts if task breaks - watchdog):
 *    @reboot while sleep 1; do cd /home/lozza && /usr/bin/php cron.php ; done
 */

class pid
{
    protected $pidfile;
    public $running = false;

    public function __construct($directory = '')
    {
        $this->pidfile = (!empty($directory) ? $directory.'/' : null) . basename($_SERVER['PHP_SELF']) . '.pid';

        if (is_writable($this->pidfile) || is_writable($directory)) {
            if (file_exists($this->pidfile)) {

                $pid = (int) trim(file_get_contents($this->pidfile));

                if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
                    $wmi = new COM("winmgmts:{impersonationLevel=impersonate}!\\\\.\\root\\cimv2");
                    $procs = $wmi->ExecQuery("SELECT * FROM Win32_Process WHERE ProcessId='".$pid."'");
                    foreach ($procs as $proc) {
                        $proc->Terminate();
                        $this->running = true;
                    }
                } else {
                    if (posix_kill($pid, 0)) {
                        $this->running = true;
                    }
                }
            }
        } else {
            die("Cannot write to pid file '{$this->pidfile}'. Program execution halted.\n");
        }

        if (!$this->running) {
            file_put_contents($this->pidfile, getmypid());
        }
    }

    public function __destruct()
    {
        if (!$this->running && file_exists($this->pidfile) && is_writeable($this->pidfile)) {
            unlink($this->pidfile);
        }
    }
}

$pid = new pid(dirname(__FILE__));

if ($pid->running) {
    exit;
} else {
    $stopTime = microtime(true) + 60;
    $i = 1;
    while (microtime(true) < $stopTime) {
        // time iteration as not to be running when next cron runs ...
        $loopStart = microtime(true);

        ### do your code
        //echo $i.PHP_EOL;
        $i++;
        
        // stop if next task will overrun minute
        if ((microtime(true)+(microtime(true) - $loopStart)) > $stopTime) {
            break;
        }

        // Run 943995 times within the minute = usleep(1000) = slow but dont 100% CPU
        usleep(1000);

        // without!
        // Run 19037412 times within the minute, but 100% CPU
        //usleep(0);
    }
    echo 'Run '.$i.' times within the minute'.PHP_EOL;
}