php background process example (create zip archive)

<?php

class zip {
  // Additional arguments passed to zip binary
  protected $zipArgs;
  // Source file or directory
  protected $src;
  // Destination file (the .zip file)
  protected $dst;
  // Process ID of the zip process
  protected $pid=0;
  // Console output of the zip process.
  // NOTE: If the command is successfull the file will be deleted
  protected $consoleOut;
  // Success state cache
  protected $success=null;

  // Constructor
  function __construct($src, $dst, $zipArgs='') {
    if (!file_exists($src))
      throw new Exceprion("File ${file} does not exist");
    elseif (file_exists($dst) && !is_writeable($dst))
      throw new Exceprion("File ${dst} is not writeable");
    elseif (!file_exists($dst) && !is_writeable(dirname($dst)))
      throw new Exceprion("File ${dst} cannot be created");

    $this->src=$src;
    $this->dst=$dst;
  }

  // Execute the zip command
  // The command wil build the zip and write its output to a tempfile
  // If everything getting fine, the tempfile will be removed. This allows
  // yo to check if the command was successfully.
  // Return integer pid
  public function zip() {
    $this->success=null;
    $this->consoleOut=tempnam(sys_get_temp_dir(), 'Zip');

    if (is_dir($this->src)) {
      $this->zipArgs .= ' -r'; // rkursive pack dirs
    }

    // echo $cmd;
    $cmd = sprintf(
      'zip %s %s %s > %s 2>&1 && rm -f %s > /dev/null 2>&1 & echo $!',
      $this->zipArgs,
      $this->dst,
      $this->src,
      $this->consoleOut,
      $this->consoleOut
    );

    return $this->pid = shell_exec($cmd);
    }


  // Blocking function, waiting until the zip command has finished
  // return boolean success state
  public function waitForFinish($ms=500) {
    while(1) {
      if (!$this->isRunning()) return $this->isSuccess();
      // Reset time limit
      set_time_limit(ini_get('max_execution_time'));
      usleep($ms);
    }
  }

  // Check if the command is still running
  // return boolean
  public function isRunning()
    {
    $cmd=sprintf('ps -p %d > /dev/null 2>&1', $this->pid);
    $exit=false;
    system($cmd, $exit);
    if ($exit === 0) return true;
    else return false;
    }


  // Check if the command was successfull
  // return boolean
  public function isSuccess()
    {
    if ($this->success !== null)
      return $this->success;
    elseif ($this->pid === 0)
      throw new Exception('No zip file created jet');
    elseif ($this->isRunning())
      return false;
    else
      return !file_exists($this->consoleOut);
    }


  // Get the the command output (stdout&stderr).
  // File is only available on failure
  public function getOutput() {
    if ($this->pid === 0)
      throw new Exception('No zip file created jet');
    elseif (!file_exists($this->consoleOut))
      return 'OK';
    else
      return file_get_contents($this->consoleOut);
  }
}