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PhutilFileLock.php
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Wed, Dec 11, 22:29

PhutilFileLock.php
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<?php
/**
* Wrapper around `flock()` for advisory filesystem locking. Usage is
* straightforward:
*
* $path = '/path/to/lock.file';
* $lock = new PhutilFileLock($path);
* $lock->lock();
*
* do_contentious_things();
*
* $lock->unlock();
*
* For more information on locks, see @{class:PhutilLock}.
*
* @task construct Constructing Locks
* @task impl Implementation
*
* @group filesystem
*/
final class PhutilFileLock extends PhutilLock {
private $lockfile;
private $handle;
/* -( Constructing Locks )------------------------------------------------- */
/**
* Create a new lock on a lockfile. The file need not exist yet.
*
* @param string The lockfile to use.
* @return PhutilFileLock New lock object.
*
* @task construct
*/
public static function newForPath($lockfile) {
$lockfile = Filesystem::resolvePath($lockfile);
$name = 'file:'.$lockfile;
$lock = self::getLock($name);
if (!$lock) {
$lock = new PhutilFileLock($name);
$lock->lockfile = $lockfile;
self::registerLock($lock);
}
return $lock;
}
/* -( Locking )------------------------------------------------------------ */
/**
* Acquire the lock. If lock acquisition fails because the lock is held by
* another process, throws @{class:PhutilLockException}. Other exceptions
* indicate that lock acquisition has failed for reasons unrelated to locking.
*
* If the lock is already held, this method throws. You can test the lock
* status with @{method:isLocked}.
*
* @param float Seconds to block waiting for the lock.
* @return void
*
* @task lock
*/
protected function doLock($wait) {
$path = $this->lockfile;
$handle = @fopen($path, 'a+');
if (!$handle) {
throw new FilesystemException(
$path,
"Unable to open lock '{$path}' for writing!");
}
$start_time = microtime(true);
do {
$would_block = null;
$ok = flock($handle, LOCK_EX | LOCK_NB, $would_block);
if ($ok) {
break;
} else {
usleep(10000);
}
} while ($wait && $wait > (microtime(true) - $start_time));
if (!$ok) {
fclose($handle);
throw new PhutilLockException($this->getName());
}
$this->handle = $handle;
}
/**
* Release the lock. Throws an exception on failure, e.g. if the lock is not
* currently held.
*
* @return void
*
* @task lock
*/
protected function doUnlock() {
$ok = flock($this->handle, LOCK_UN | LOCK_NB);
if (!$ok) {
throw new Exception("Unable to unlock file!");
}
$ok = fclose($this->handle);
if (!$ok) {
throw new Exception("Unable to close file!");
}
$this->handle = null;
}
}

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