(PHP 3>= 3.0.7, PHP 4 >= 4.0.0)
flock -- Portable advisory file locking
Description
bool
flock ( int fp, int operation [, int wouldblock])
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).
flock() operates on fp
which must be an open file
pointer. operation is one of the following
values:
To acquire a shared lock (reader), set
operation to LOCK_SH (set to 1 prior to
PHP 4.0.1).
To acquire an exclusive lock (writer), set
operation to LOCK_EX (set to 2 prior to
PHP 4.0.1).
To release a lock (shared or exclusive), set
operation to LOCK_UN (set to 3 prior to
PHP 4.0.1).
If you don't want flock() to block while
locking, add LOCK_NB (4 prior to PHP 4.0.1) to
operation.
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 optional third
argument is set to TRUE if the lock would block (EWOULDBLOCK
errno condition)
flock() returns TRUE on success and FALSE on
error (e.g. when a lock could not be acquired).
Note:
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()).
| Warning |
flock() will not work on NFS and many other networked
file systems. Check your operating system documentation for more
details.
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!
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