flock

flock

Portable advisory file locking

bool **flock** resource $stream int $operation int $would_block

allows you to perform a simple reader/writer

model which can be used on virtually every platform (including most Unix derivatives and even Windows). flock

The lock is released also by , or when is garbage collected. fclose``stream

PHP supports a portable way of locking complete files in an advisory way (which means all accessing programs have to use the same way of locking or it will not work). By default, this function will block until the requested lock is acquired; this may be controlled with the option documented below. LOCK_NB

stream``operation is one of the following:

  `operation`- to acquire a shared lock (reader).          `LOCK_SH`

• to acquire an exclusive lock (writer). LOCK_EX

• to release a lock (shared or exclusive). LOCK_UN

   It is also possible to add  as a bitmask to one 
   of the above operations, if  should not
   block during the locking attempt.
  `LOCK_NB``flock`
  

would_blockThe optional third argument is set to 1 if the lock would block (EWOULDBLOCK errno condition).

return.success

Voorbeeld: example

<?php

$fp = fopen("/tmp/lock.txt", "r+");

if (flock($fp, LOCK_EX)) {  // acquire an exclusive lock
    ftruncate($fp, 0);      // truncate file
    fwrite($fp, "Write something here\n");
    fflush($fp);            // flush output before releasing the lock
    flock($fp, LOCK_UN);    // release the lock
} else {
    echo "Couldn't get the lock!";
}

fclose($fp);

?>

Voorbeeld: using the option

<?php
$fp = fopen('/tmp/lock.txt', 'r+');

/* Activate the LOCK_NB option on an LOCK_EX operation */
if(!flock($fp, LOCK_EX | LOCK_NB)) {
    echo 'Unable to obtain lock';
    exit(-1);
}

/* ... */

fclose($fp);
?>

Opmerking: > uses mandatory locking instead of advisory locking on Windows. Mandatory locking is also supported on Linux and System V based operating systems via the usual mechanism supported by the fcntl() system call: that is, if the file in question has the setgid permission bit set and the group execution bit cleared. On Linux, the file system will also need to be mounted with the mand option for this to work. flock

Opmerking: > Because requires a file pointer, you may have to use a special lock file to protect access to a file that you intend to truncate by opening it in write mode (with a "w" or "w+" argument to ). flock``fopen

Opmerking: > May only be used on file pointers returned by for local files, or file pointers pointing to userspace streams that implement the method. fopen``streamWrapper::stream_lock

Waarschuwing: > Assigning another value to argument in subsequent code will release the lock. stream

Waarschuwing: > On some operating systems is implemented at the process level. When using a multithreaded server API you may not be able to rely on to protect files against other PHP scripts running in parallel threads of the same server instance! flock``flock

 is not supported on antiquated filesystems like
 and its derivates and will therefore always
return false under these environments.

flock``FAT

Opmerking: > On Windows, if the locking process opens the file a second time, it cannot access the file through this second handle until it unlocks the file.