com.twitter.zk.coordination

ZkAsyncSemaphore

class ZkAsyncSemaphore extends AnyRef

ZkAsyncSemaphore is a distributed semaphore with asynchronous execution. Grabbing a permit constitutes a vote on the number of permits the semaphore can permit and returns a Future[Permit]. If consensus on the number of permits is lost, an exception is raised when acquiring a permit (so expect it).

Care must be taken to handle zookeeper client session expiry. A ZkAsyncSemaphore cannot be used after the zookeeper session has expired. Likewise, any permits acquired via the session must be considered invalid. Additionally, it is the client's responsibility to determine if a permit is still valid in the case that the zookeeper client becomes disconnected.

Attempts to clone AsyncSemaphore

Ex.

implicit val timer = new JavaTimer(true)
val connector = NativeConnector("localhost:2181", 5.seconds, 10.minutes)
val zk = ZkClient(connector).withRetryPolicy(RetryPolicy.Basic(3))
val path = "/testing/twitter/service/charm/shards"
val sem = new ZkAsyncSemaphore(zk, path, 4)

sem.acquire flatMap { permit =>
  Future { ... } ensure { permit.release }
} // handle { ... }
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Instance Constructors

  1. new ZkAsyncSemaphore(zk: ZkClient, path: String, numPermits: Int, maxWaiters: Option[Int] = scala.None)

Value Members

  1. final def !=(arg0: AnyRef): Boolean

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  2. final def !=(arg0: Any): Boolean

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  3. final def ##(): Int

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  4. final def ==(arg0: AnyRef): Boolean

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  5. final def ==(arg0: Any): Boolean

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  6. def acquire(): Future[Permit]

  7. final def asInstanceOf[T0]: T0

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  8. def clone(): AnyRef

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  11. def finalize(): Unit

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  16. final def notify(): Unit

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  17. final def notifyAll(): Unit

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  18. var numPermitsAvailable: Int

  19. var numWaiters: Int

  20. final def synchronized[T0](arg0: ⇒ T0): T0

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  21. def toString(): String

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  22. final def wait(): Unit

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  23. final def wait(arg0: Long, arg1: Int): Unit

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  24. final def wait(arg0: Long): Unit

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