问在php中获得锁的最好方法

EN

/*
CLASS ExclusiveLock
Description
==================================================================
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();
===================================================================
*/
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
    }
};

  $value = apc_fetch($KEY);

  if ($value === FALSE) {
      shm_acquire($SEMAPHORE);

      $recheck_value = apc_fetch($KEY);
      if ($recheck_value !== FALSE) {
        $new_value = expensive_operation();
        apc_store($KEY, $new_value);
        $value = $new_value;
      } else {
        $value = $recheck_value;
      }

      shm_release($SEMAPHORE);
   }

$f = fopen("lockFile.txt", 'x');
if($f) {
    $me = getmypid();
    $now = date('Y-m-d H:i:s');
    fwrite($f, "Locked by $me at $now\n");
    fclose($f);
    doStuffInLock();
    unlink("lockFile.txt"); // unlock        
}
else {
    echo "File is locked: " . file_get_contents("lockFile.txt");
    exit;
}