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PhutilLock.php
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Sun, Apr 28, 18:36

PhutilLock.php
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<?php
/**
* Base class for locks, like file locks.
*
* libphutil provides a concrete lock in @{class:PhutilFileLock}.
*
* $lock->lock();
* do_contentious_things();
* $lock->unlock();
*
* If the lock can't be acquired because it is already held,
* @{class:PhutilLockException} is thrown. Other exceptions indicate
* permanent failure unrelated to locking.
*
* When extending this class, you should call @{method:getLock} to look up
* an existing lock object, and @{method:registerLock} when objects are
* constructed to register for automatic unlock on shutdown.
*
* @task impl Lock Implementation
* @task registry Lock Registry
* @task construct Constructing Locks
* @task status Determining Lock Status
* @task lock Locking
* @task internal Internals
*
* @group filesystem
*/
abstract class PhutilLock {
private static $registeredShutdownFunction = false;
private static $locks = array();
private $locked = false;
private $profilerID;
private $name;
/* -( Constructing Locks )------------------------------------------------- */
/**
* Build a new lock, given a lock name. The name should be globally unique
* across all locks.
*
* @param string Globally unique lock name.
* @task construct
*/
protected function __construct($name) {
$this->name = $name;
}
/* -( Lock Implementation )------------------------------------------------ */
/**
* Acquires the lock, or throws @{class:PhutilLockException} if it fails.
*
* @param float Seconds to block waiting for the lock.
* @return void
* @task impl
*/
abstract protected function doLock($wait);
/**
* Releases the lock.
*
* @return void
* @task impl
*/
abstract protected function doUnlock();
/* -( Lock Registry )------------------------------------------------------ */
/**
* Returns a globally unique name for this lock.
*
* @return string Globally unique lock name, across all locks.
* @task registry
*/
final public function getName() {
return $this->name;
}
/**
* Get a named lock, if it has been registered.
*
* @param string Lock name.
* @task registry
*/
protected static function getLock($name) {
return idx(self::$locks, $name);
}
/**
* Register a lock for cleanup when the process exits.
*
* @param PhutilLock Lock to register.
* @task registry
*/
protected static function registerLock(PhutilLock $lock) {
if (!self::$registeredShutdownFunction) {
register_shutdown_function(array('PhutilLock', 'unlockAll'));
self::$registeredShutdownFunction = true;
}
$name = $lock->getName();
if (self::getLock($name)) {
throw new Exception("Lock '{$name}' is already registered!");
}
self::$locks[$name] = $lock;
}
/* -( Determining Lock Status )-------------------------------------------- */
/**
* Determine if the lock is currently held.
*
* @return bool True if the lock is held.
*
* @task status
*/
final public function isLocked() {
return $this->locked;
}
/* -( Locking )------------------------------------------------------------ */
/**
* Acquire the lock. If lock acquisition fails because the lock is held by
* another process, throws @{class:PhutilLockException}. Other exceptions
* indicate that lock acquisition has failed for reasons unrelated to locking.
*
* If the lock is already held by this process, this method throws. You can
* test the lock status with @{method:isLocked}.
*
* @param float Seconds to block waiting for the lock. By default, do not
* block.
* @return this
*
* @task lock
*/
final public function lock($wait = 0) {
if ($this->locked) {
$name = $this->getName();
throw new Exception(
"Lock '{$name}' has already been locked by this process.");
}
$profiler = PhutilServiceProfiler::getInstance();
$profiler_id = $profiler->beginServiceCall(
array(
'type' => 'lock',
'name' => $this->getName(),
));
try {
$this->doLock((float)$wait);
} catch (Exception $ex) {
$profiler->endServiceCall(
$profiler_id,
array(
'lock' => false,
));
throw $ex;
}
$this->profilerID = $profiler_id;
$this->locked = true;
return $this;
}
/**
* Release the lock. Throws an exception on failure, e.g. if the lock is not
* currently held.
*
* @return this
*
* @task lock
*/
final public function unlock() {
if (!$this->locked) {
$name = $this->getName();
throw new Exception(
"Lock '{$name} is not locked by this process!");
}
$this->doUnlock();
$profiler = PhutilServiceProfiler::getInstance();
$profiler->endServiceCall(
$this->profilerID,
array(
'lock' => true,
));
$this->profilerID = null;
$this->locked = false;
return $this;
}
/* -( Internals )---------------------------------------------------------- */
/**
* On shutdown, we release all the locks. You should not call this method
* directly. Use @{method:unlock} to release individual locks.
*
* @return void
*
* @task internal
*/
public static function unlockAll() {
foreach (self::$locks as $key => $lock) {
if ($lock->locked) {
$lock->unlock();
}
}
}
}

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