flock Portable advisory file locking &reftitle.description; boolflock resourcehandle intoperation intwouldblock flock allows you to perform a simple reader/writer model which can be used on virtually every platform (including most Unix derivatives and even Windows). The lock is released also by fclose (which is also called automatically when script finished). 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 (on non-Windows platforms) with the LOCK_NB option documented below. &reftitle.parameters; handle An open file pointer. operation operation is one of the following: LOCK_SH to acquire a shared lock (reader). LOCK_EX to acquire an exclusive lock (writer). LOCK_UN to release a lock (shared or exclusive). It is also possible to add LOCK_NB as a bitmask to one of the above operations if you don't want flock to block while locking. (not supported on Windows) wouldblock The optional third argument is set to &true; if the lock would block (EWOULDBLOCK errno condition). (not supported on Windows) &reftitle.returnvalues; &return.success; &reftitle.changelog; &Version; &Description; 5.3.2 The automatic unlocking when the file's resource handle is closed was removed. Unlocking now always has to be done manually. 4.0.1 The LOCK_XXX constants were added. Prior to that you must use 1 for LOCK_SH, 2 for LOCK_EX, 3 for LOCK_UN and 4 for LOCK_NB &reftitle.examples; ]]> ]]> &reftitle.notes; flock locks mandatory under Windows aswell as some POSIX based operating systems. Because flock 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 fopen). Assigning other value to handle argument in the consecutive code would release the lock. On some operating systems flock is implemented at the process level. When using a multithreaded server API like ISAPI you may not be able to rely on flock to protect files against other PHP scripts running in parallel threads of the same server instance! flock is not supported on antiquated filesystems like FAT and its derivates and will therefore always return &false; under this environments (this is especially true for Windows 98 users).