PHP/File Directory/flock

If file lock is not available, flock( ) will return immediately with false rather than wait for a lock to become available.

   <source lang="html4strict">

<?

   $fp = fopen("foo.txt", "w");
   if (flock($fp, LOCK_EX | LOCK_NB)) {
           echo "Got lock!\n";
           sleep(10);
           flock($fp, LOCK_UN);
   } else {
           print "Could not get lock!\n";
   }

?>

 </source>
   
  

Locking Files with flock( )

   <source lang="html4strict">

<?

   $fp = fopen( $filename,"w"); // open it for WRITING ("w")
   if (flock($fp, LOCK_EX)) {
           // do your file writes here
           flock($fp, LOCK_UN); // unlock the file
   } else {
           // flock( ) returned false, no lock obtained
           print "Could not lock $filename!\n";
   }

?>

 </source>
   
  

The file locking mechanism in PHP makes processes queue up for their locks by default

   <source lang="html4strict">

<?

   $fp = fopen("foo.txt", "w");
   if (flock($fp, LOCK_EX)) {
           print "Got lock!\n";
           sleep(10);
           flock($fp, LOCK_UN);
   }

?>

 </source>
   
  

Using advisory file locking

   <source lang="html4strict">

<?php $fh = fopen("guestbook.txt","a") or die($php_errormsg); flock($fh,LOCK_EX) or die($php_errormsg); fwrite($fh,$_POST["guestbook_entry"]) or die($php_errormsg); fflush($fh) or die($php_errormsg); flock($fh,LOCK_UN) or die($php_errormsg); fclose($fh) or die($php_errormsg); ?>

 </source>