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.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.cassandra.utils.concurrent.Condition

Condition.Async, Condition.Sync

Nested classes/interfaces inherited from interface org.apache.cassandra.utils.concurrent.Awaitable

Awaitable.AbstractAwaitable, Awaitable.AsyncAwaitable, Awaitable.Defaults, Awaitable.SyncAwaitable

Method Summary

Modifier and Type	Method and Description
void	cancel() Should only be called by the owning thread.
boolean	checkAndClear() atomically: cancels the Signal if !isSet(), or returns true if isSignalled()
boolean	isCancelled()
boolean	isSet()

Methods inherited from interface org.apache.cassandra.utils.concurrent.Condition

isSignalled, newOneTimeCondition, signal, signalAll

Methods inherited from interface org.apache.cassandra.utils.concurrent.Awaitable

await, await, awaitThrowUncheckedOnInterrupt, awaitThrowUncheckedOnInterrupt, awaitUninterruptibly, awaitUninterruptibly, awaitUntil, awaitUntilThrowUncheckedOnInterrupt, awaitUntilUninterruptibly

Method Detail

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 isSignalled()

Returns:

true if isSignalled()

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