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Programming PHP, 3rd Edition by Peter MacIntyre, Kevin Tatroe, Rasmus Lerdorf

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Name

flock

Synopsis

bool flock(resource handle, int operation[, int would_block])

Attempts to lock the file path of the file specified by handle. The operation is one of the following values:

LOCK_SH

Shared lock (reader)

LOCK_EX

Exclusive lock (writer)

LOCK_UN

Release a lock (either shared or exclusive)

LOCK_NB

Add to LOCK_SH or LOCK_EX to obtain a nonblocking lock

If specified, would_block is set to true if the operation would cause a block on the file. The function returns false if the lock could not be obtained, and true if the operation succeeded.

Because file locking is implemented at the process level on most systems, flock() cannot prevent two PHP scripts running in the same web server process from accessing a file at the same time.

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