function mutexAcquireLock($filename, $timeout){
	$fp = @fopen($filename . '.lck', 'x');
	if($fp === false) return false;
	if(false === @fwrite($fp, time() + $timeout)) return false;
	return fclose($fp);
}

function mutexReleaseLock($filename){
	return @unlink($filename . '.lck');
}

<?php
for($i = 0; $i < 10; $i++){
	fwrite(STDOUT, getmypid() . ": ");
	if(!mutexAcquireLock('mutex.php', 2)){
		fwrite(STDOUT, "Failed lock\n");
		sleep(2);
	}else{
		fwrite(STDOUT, "Lock acquired -> ");
		if(!mutexReleaseLock('mutex.php')){
			fwrite(STDOUT, "File not locked" . "\n");
		}else{
			fwrite(STDOUT, "Lock released" . "\n");
		}
		sleep(2);
	}
}

function mutexAcquireLock($filename, $timeout){
	$fp = @fopen($filename . '.lck', 'x');
	if($fp === false) return false;
	if(false === @fwrite($fp, time() + $timeout)) return false;
	return fclose($fp);
}

function mutexReleaseLock($filename){
	return @unlink($filename . '.lck');
}
?>

<?php
for($i = 0; $i < 20; $i++){
	fwrite(STDOUT, getmypid() . ": ");
	if(!mutexAcquireLock('mutex.php', 2)){
		fwrite(STDOUT, "Lock failed -> ");
		$tiempo = mutexTimeOut('mutex.php');
		if($tiempo !== false && $tiempo < 0){
			if(!mutexReleaseLock('mutex.php')){
				fwrite(STDOUT, "Unable to forcibly remove lock" . "\n");
			}else{
				fwrite(STDOUT, "Lock forcibly removed" . "\n");
			}
		}
		sleep(1);
	}else{
		fwrite(STDOUT, "Lock acquired -> ");
		if($i != 10){
			if(!mutexReleaseLock('mutex.php')){
				fwrite(STDOUT, "File not locked" . "\n");
			}else{
				fwrite(STDOUT, "Lock released" . "\n");
			}
		}else{
			sleep(5);
		}
		sleep(1);
	}
}

function mutexAcquireLock($filename, $timeout){
	$fp = @fopen($filename . '.lck', 'x');
	if($fp === false) return false;
	if(!@chmod($filename . '.lck', 0755)) return false;
	if(false === @fwrite($fp, time() + $timeout)) return false;
	return fclose($fp);
}

function mutexReleaseLock($filename){
	return @unlink($filename . '.lck');
}

function mutexTimeOut($filename){
	$timeout = @file_get_contents($filename . '.lck');
	if($timeout === false) return false;
	return intval($timeout) - time();
}
?>

<?php
error_reporting(E_ALL);
 
/* Reference Material
 *
 * http://en.wikipedia.org/wiki/ACID
 *
 */
 
class Mutex {
	/* Private variables */
 
	var $filename;          // The file to be locked
	var $timeout;           // The timeout value of the lock
	var $permission = 0755; // The permission value of the locked file
 
	/* Constructor */
 
	function Mutex($filename, $timeout = 1, $permission = null){
		// Append '.lck' extension to filename for the locking mechanism
		$this->filename = $filename . '.lck';
		// Timeout should be some factor greater than the maximum script execution time
		if($timeout < 1) $this->timeout = get_cfg_var('max_execution_time');
		else $this->timeout = $timeout * get_cfg_var('max_execution_time');
		// Should some other permission value be necessary
		if(isset($permission)) $this->permission = $permission;
	}
 
	/* Methods */
 
	function acquireLock(){
		// Create the locked file, the 'x' parameter is used to detect a preexisting lock
		$fp = @fopen($this->filename, 'x');
		// If an error occurs fail lock
		if($fp === false) return false;
		// If the permission set is unsuccessful fail lock
		if(!@chmod($this->filename, $this->permission)) return false;
		// If unable to write the timeout value fail lock
		if(false === @fwrite($fp, time() + intval($this->timeout))) return false;
		// If lock is successfully closed validate lock
		return fclose($fp);
	}
 
	function releaseLock(){
		// Delete the file with the extension '.lck'
		return @unlink($this->filename);
	}
 
	function timeLock(){
		// Retrieve the contents of the lock file
		$timeout = @file_get_contents($this->filename);
		// If no contents retrieved return error
		if($timeout === false) return false;
		// Return the timeout value
		return intval($timeout);
	}
}
?>