* minutes and hundreds of read hits.
*
* The PoolCounter provides semaphore semantics for restricting the number
- * of workers that may be concurrently performing such single task.
+ * of workers that may be concurrently performing such single task. Only one
+ * key can be locked by any PoolCounter instance of a process, except for keys
+ * that start with "nowait:". However, only 0 timeouts (non-blocking requests)
+ * can be used with "nowait:" keys.
*
* By default PoolCounter_Stub is used, which provides no locking. You
* can get a useful one in the PoolCounter extension.
/** @var float Maximum time in seconds to wait for the lock */
protected $timeout;
+ /**
+ * @var boolean Whether the key is a "might wait" key
+ */
+ private $isMightWaitKey;
+ /**
+ * @var boolean Whether this process holds a "might wait" lock key
+ */
+ private static $acquiredMightWaitKey = 0;
+
/**
* @param array $conf
* @param string $type
$key = $this->hashKeyIntoSlots( $key, $this->slots );
}
$this->key = $key;
+ $this->isMightWaitKey = !preg_match( '/^nowait:/', $this->key );
}
/**
*/
abstract public function release();
+ /**
+ * Checks that the lock request is sane.
+ * @return Status - good for sane requests fatal for insane
+ * @since 1.25
+ */
+ final protected function precheckAcquire() {
+ if ( $this->isMightWaitKey ) {
+ if ( self::$acquiredMightWaitKey ) {
+ /*
+ * The poolcounter itself is quite happy to allow you to wait
+ * on another lock while you have a lock you waited on already
+ * but we think that it is unlikely to be a good idea. So we
+ * made it an error. If you are _really_ _really_ sure it is a
+ * good idea then feel free to implement an unsafe flag or
+ * something.
+ */
+ return Status::newFatal( 'poolcounter-usage-error',
+ 'You may only aquire a single non-nowait lock.' );
+ }
+ } elseif ( $this->timeout !== 0 ) {
+ return Status::newFatal( 'poolcounter-usage-error',
+ 'Locks starting in nowait: must have 0 timeout.' );
+ }
+ return Status::newGood();
+ }
+
+ /**
+ * Update any lock tracking information when the lock is acquired
+ * @since 1.25
+ */
+ final protected function onAcquire() {
+ self::$acquiredMightWaitKey |= $this->isMightWaitKey;
+ }
+
+ /**
+ * Update any lock tracking information when the lock is released
+ * @since 1.25
+ */
+ final protected function onRelease() {
+ self::$acquiredMightWaitKey &= !$this->isMightWaitKey;
+ }
+
/**
* Given a key (any string) and the number of lots, returns a slot number (an integer from the [0..($slots-1)] range).
* This is used for a global limit on the number of instances of a given type that can acquire a lock.