* 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 string All workers with the same key share the lock */
protected $key;
- /** @var int Maximum number of workers doing the task simultaneously */
+ /** @var int Maximum number of workers working on tasks with the same key simultaneously */
protected $workers;
+ /**
+ * Maximum number of workers working on this task type, regardless of key.
+ * 0 means unlimited. Max allowed value is 65536.
+ * The way the slot limit is enforced is overzealous - this option should be used with caution.
+ * @var int
+ */
+ protected $slots = 0;
/** @var int If this number of workers are already working/waiting, fail instead of wait */
protected $maxqueue;
/** @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
* @param string $key
*/
protected function __construct( $conf, $type, $key ) {
- $this->key = $key;
$this->workers = $conf['workers'];
$this->maxqueue = $conf['maxqueue'];
$this->timeout = $conf['timeout'];
+ if ( isset( $conf['slots'] ) ) {
+ $this->slots = $conf['slots'];
+ }
+
+ if ( $this->slots ) {
+ $key = $this->hashKeyIntoSlots( $key, $this->slots );
+ }
+ $this->key = $key;
+ $this->isMightWaitKey = !preg_match( '/^nowait:/', $this->key );
}
/**
* Lets another one grab the lock, and returns the workers
* waiting on acquireForAnyone()
*
- * @return Status value is one of Released/NotLocked/Error
+ * @return Status Value is one of Released/NotLocked/Error
*/
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.
+ * The hashing is deterministic so that PoolCounter::$workers is always an upper limit of how many instances with
+ * the same key can acquire a lock.
+ *
+ * @param string $key PoolCounter instance key (any string)
+ * @param int $slots The number of slots (max allowed value is 65536)
+ * @return int
+ */
+ protected function hashKeyIntoSlots( $key, $slots ) {
+ return hexdec( substr( sha1( $key ), 0, 4 ) ) % $slots;
+ }
}
// @codingStandardsIgnoreStart Squiz.Classes.ValidClassName.NotCamelCaps