org.apache.druid.concurrent

Class LifecycleLock

java.lang.Object

org.apache.druid.concurrent.LifecycleLock

public class LifecycleLock
extends Object

A synchronization tool for lifecycled objects (see Lifecycle, that need happens-before between start() and other methods and/or to check that the object was successfully started in other methods. Guarantees in terms of JMM: happens-before between exitStart() and awaitStarted(), exitStart() and canStop(), if it returns true. Example: class ExampleLifecycledClass { final LifecycleLock lifecycleLock = new LifecycleLock(); void start() { if (!lifecycleLock.canStart()) { .. return or throw exception } try { .. do start lifecycleLock.started(); } finally { lifecycleLock.exitStart(); } } void otherMethod() { Preconditions.checkState(lifecycleLock.awaitStarted()); // all actions done in start() are visible here .. do stuff } void stop() { if (!lifecycleLock.canStop()) { .. return or throw exception } // all actions done in start() are visible here .. do stop } }

Constructor Summary

Constructors

Constructor and Description
LifecycleLock()

Method Summary

Modifier and Type	Method and Description
boolean	awaitStarted() Awaits until exitStart() is called, if needed, and returns true if started() was called before that.
boolean	awaitStarted(long timeout, TimeUnit unit) Awaits until exitStart() is called for at most the specified timeout, and returns true if started() was called before that.
boolean	canStart() Start latch, only one canStart() call in any thread on this LifecycleLock object could return true, if exitStopAndReset() is not called in between.
boolean	canStop() Stop latch, only one canStop() call in any thread on this LifecycleLock object could return true.
void	exitStart() Must be called before exit from start() on the lifecycled object, usually in a finally block.
void	exitStop() Finalizes stopping the LifecycleLock.
void	exitStopAndReset() Finalizes stopping the LifecycleLock and resets it, so that canStart() could be called again.
boolean	isStarted() Returns true if started() was called before that.
void	started() Announce the start was successful.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LifecycleLock

public LifecycleLock()

Method Detail

canStart

public boolean canStart()

Start latch, only one canStart() call in any thread on this LifecycleLock object could return true, if exitStopAndReset() is not called in between.

started

public void started()

Announce the start was successful.

Throws:

IllegalMonitorStateException - if canStart() is not yet called or if exitStart() is already called on this LifecycleLock

exitStart

public void exitStart()

Must be called before exit from start() on the lifecycled object, usually in a finally block.

Throws:

IllegalMonitorStateException - if canStart() is not yet called on this LifecycleLock

isStarted

public boolean isStarted()

Returns true if started() was called before that. Returns false if started() is not called before exitStart(), or if canStop() is already called on this LifecycleLock.

awaitStarted

public boolean awaitStarted()

Awaits until exitStart() is called, if needed, and returns true if started() was called before that. Returns false if started() is not called before exitStart(), or if canStop() is already called on this LifecycleLock.

awaitStarted

public boolean awaitStarted(long timeout,
                            TimeUnit unit)

Awaits until exitStart() is called for at most the specified timeout, and returns true if started() was called before that. Returns false if started() wasn't called before exitStart(), or if exitStart() isn't called on this LifecycleLock until the specified timeout expires, or if canStop() is already called on this LifecycleLock.

canStop

public boolean canStop()

Stop latch, only one canStop() call in any thread on this LifecycleLock object could return true. If started() wasn't called on this LifecycleLock object, always returns false.

Throws:

IllegalMonitorStateException - if exitStart() are not yet called on this LifecycleLock

exitStop

public void exitStop()

Finalizes stopping the LifecycleLock. This method must be called before exit from stop() on this object, usually in a finally block. If you're using a restartable object, use exitStopAndReset() instead.

Throws:

IllegalMonitorStateException - if canStop() is not yet called on this LifecycleLock

exitStopAndReset

public void exitStopAndReset()

Finalizes stopping the LifecycleLock and resets it, so that canStart() could be called again. If this LifecycleLock is used in a restartable object, this method must be called before exit from stop() on this object, usually in a finally block.

Throws:

IllegalMonitorStateException - if canStop() is not yet called on this LifecycleLock