PHP: SplFileObject::flock - Manual

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

SplFileObject::flock — Portable file locking

Description

public function SplFileObject::flock(int $operation, int &$wouldBlock = null): bool

Parameters

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 flock() should not block during the locking attempt.

wouldBlock

Set to true if the lock would block (EWOULDBLOCK errno condition).

Return Values

Returns true on success or false on failure.

Examples

<?php
$file = new SplFileObject("/tmp/lock.txt", "w");
if ($file->flock(LOCK_EX)) { // do an exclusive lock
    $file->ftruncate(0);     // truncate file
    $file->fwrite("Write something here\n");
    $file->flock(LOCK_UN);   // release the lock    
} else {
    echo "Couldn't get the lock!";
}
?>

See Also

• flock() - Portable advisory file locking

digitalprecision at gmail dot com ¶

15 years ago

For the record, the example given here has an explicit command to truncate the file, however with a 'write mode' of 'w', it will do this for you automatically, so the truncate call is not needed.

Ahmed Rain ¶

3 years ago

@digitalprecision What you said is not completely true, ftruncate(0); is needed if there was a write to the file before the lock is acquired. You also may need fseek(0); to move back the file pointer to the beginning of the file

<?php
$file = new SplFileObject("/tmp/lock.txt", "w");
$file->fwrite("xxxxx"); // write something before the lock is acquired
sleep(5); // wait for 5 seconds

if ($file->flock(LOCK_EX)) { // do an exclusive lock
    $file->fwrite("Write something here\n");
    $file->flock(LOCK_UN);   // release the lock    
} else {
    echo "Couldn't get the lock!";
}
?>

"lock.txt" content:

xxxxxWrite something here