Package org.apache.cassandra.utils.concurrent

Interface WaitQueue.Signal

All Superinterfaces:
Awaitable, Condition
All Known Implementing Classes:
WaitQueue.Standard.AbstractSignal
Enclosing interface:
WaitQueue
public static interface WaitQueue.Signal extends Condition
A Signal is a one-time-use mechanism for a thread to wait for notification that some condition state has transitioned that it may be interested in (and hence should check if it is). It is potentially transient, i.e. the state can change in the meantime, it only indicates that it should be checked, not necessarily anything about what the expected state should be. Signal implementations should never wake up spuriously, they are always woken up by a signal() or signalAll(). This abstract definition of Signal does not need to be tied to a WaitQueue. Whilst RegisteredSignal is the main building block of Signals, this abstract definition allows us to compose Signals in useful ways. The Signal is 'owned' by the thread that registered itself with WaitQueue(s) to obtain the underlying RegisteredSignal(s); only the owning thread should use a Signal.

  • Method Details

    • isCancelled

      boolean isCancelled()
      Returns:
      true if cancelled; once cancelled, must be discarded by the owning thread.

    • isSet

      boolean isSet()
      Returns:
      isSignalled() || isCancelled(). Once true, the state is fixed and the Signal should be discarded by the owning thread.

    • checkAndClear

      boolean checkAndClear()
      atomically: cancels the Signal if !isSet(), or returns true if isSet()
      Returns:
      true if isSet()

    • cancel

      void cancel()
      Should only be called by the owning thread. Indicates the signal can be retired, and if signalled propagates the signal to another waiting thread

    • await

      Awaitable await() throws InterruptedException
      Await indefinitely, throwing any interrupt. No spurious wakeups. Important: the signal can be cancelled if the thread executing await() is interrupted
      Specified by:
      await in interface Awaitable
      Throws:
      InterruptedException - if interrupted

    • awaitUntil

      boolean awaitUntil(long nanoTimeDeadline) throws InterruptedException
      Await until the deadline (in nanoTime), throwing any interrupt. No spurious wakeups.
      Specified by:
      awaitUntil in interface Awaitable
      Returns:
      true if we were signalled, false if the deadline elapsed Important: the signal can be cancelled if the thread executing await() is interrupted
      Throws:
      InterruptedException - if interrupted