nicoorfi
11/26/2018 - 7:49 AM

PHP file lock class

This is a pseudo implementation of mutex since php does not have any thread synchronization objects This class uses flock() as a base to provide locking functionality. Lock will be released in following cases

  1. user calls unlock
  2. when this lock object gets deleted
  3. when request or script ends

Usage:

//get the lock
$lock = new ExclusiveLock( "mylock" );

//lock
if( $lock->lock( ) == FALSE )
    error("Locking failed");
//--
//Do your work here
//--

//unlock
$lock->unlock();
ExclusiveLock
content_copyfile_download
<?php

    class ExclusiveLock
    {
        protected $key = null;  //user given value
        protected $file = null;  //resource to lock
        protected $own = false; //have we locked resource

        function __construct($key)
        {

            $this->key = $key;
//create a new resource or get exisitng with same key
            $this->file = fopen("$key.lockfile", 'w+');
        }

        function __destruct()
        {

            if ($this->own == true) {
                $this->unlock();
            }
        }

        function lock()
        {

            if (!flock($this->file, LOCK_EX | LOCK_NB)) { //failed
                $key = $this->key;
                error_log("ExclusiveLock::acquire_lock FAILED to acquire lock [$key]");

                return false;
            }
            ftruncate($this->file, 0); // truncate file
//write something to just help debugging
            fwrite($this->file, "Locked\n");
            fflush($this->file);

            $this->own = true;

            return true; // success
        }

        function unlock()
        {

            $key = $this->key;
            if ($this->own == true) {
                if (!flock($this->file, LOCK_UN)) { //failed
                    error_log("ExclusiveLock::lock FAILED to release lock [$key]");

                    return false;
                }
                ftruncate($this->file, 0); // truncate file
//write something to just help debugging
                fwrite($this->file, "Unlocked\n");
                fflush($this->file);
                $this->own = false;
            } else {
                error_log("ExclusiveLock::unlock called on [$key] but its not acquired by caller");
            }

            return true; // success
        }
    };