Package com.google.common.util.concurrent

Class AbstractService

java.lang.Object

com.google.common.util.concurrent.AbstractService

All Implemented Interfaces:

Service

@GwtIncompatible
public abstract class AbstractService
extends Object
implements Service

Base class for implementing services that can handle doStart() and doStop() requests, responding to them with notifyStarted() and notifyStopped() callbacks. Its subclasses must manage threads manually; consider AbstractExecutionThreadService if you need only a single execution thread.

Since:

1.0

Author:

Jesse Wilson, Luke Sandberg

Nested Class Summary

Nested classes/interfaces inherited from interface com.google.common.util.concurrent.Service

Service.Listener, Service.State

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AbstractService()	Constructor for use by subclasses.

Method Summary

Modifier and Type	Method	Description
void	addListener(Service.Listener listener, Executor executor)	Registers a Service.Listener to be executed on the given executor.
void	awaitRunning()	Waits for the Service to reach the running state.
void	awaitRunning(long timeout, TimeUnit unit)	Waits for the Service to reach the running state for no more than the given time.
void	awaitTerminated()	Waits for the Service to reach the terminated state.
void	awaitTerminated(long timeout, TimeUnit unit)	Waits for the Service to reach a terminal state (either terminated or failed) for no more than the given time.
protected void	doCancelStart()	This method is called by stopAsync() when the service is still starting (i.e.
protected abstract void	doStart()	This method is called by startAsync() to initiate service startup.
protected abstract void	doStop()	This method should be used to initiate service shutdown.
Throwable	failureCause()	Returns the Throwable that caused this service to fail.
boolean	isRunning()	Returns true if this service is running.
protected void	notifyFailed(Throwable cause)	Invoke this method to transition the service to the Service.State.FAILED.
protected void	notifyStarted()	Implementing classes should invoke this method once their service has started.
protected void	notifyStopped()	Implementing classes should invoke this method once their service has stopped.
Service	startAsync()	If the service state is Service.State.NEW, this initiates service startup and returns immediately.
Service.State	state()	Returns the lifecycle state of the service.
Service	stopAsync()	If the service is starting or running, this initiates service shutdown and returns immediately.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractService

protected AbstractService()

Constructor for use by subclasses.

Method Detail

doStart

@ForOverride
protected abstract void doStart()

This method is called by startAsync() to initiate service startup. The invocation of this method should cause a call to notifyStarted(), either during this method's run, or after it has returned. If startup fails, the invocation should cause a call to notifyFailed(Throwable) instead.

This method should return promptly; prefer to do work on a different thread where it is convenient. It is invoked exactly once on service startup, even when startAsync() is called multiple times.

doStop

@ForOverride
protected abstract void doStop()

This method should be used to initiate service shutdown. The invocation of this method should cause a call to notifyStopped(), either during this method's run, or after it has returned. If shutdown fails, the invocation should cause a call to notifyFailed(Throwable) instead.

This method should return promptly; prefer to do work on a different thread where it is convenient. It is invoked exactly once on service shutdown, even when stopAsync() is called multiple times.

If stopAsync() is called on a Service.State.STARTING service, this method is not invoked immediately. Instead, it will be deferred until after the service is Service.State.RUNNING. Services that need to cancel startup work can override doCancelStart().

doCancelStart

@ForOverride
protected void doCancelStart()

This method is called by stopAsync() when the service is still starting (i.e. startAsync() has been called but notifyStarted() has not). Subclasses can override the method to cancel pending work and then call notifyStopped() to stop the service.

This method should return promptly; prefer to do work on a different thread where it is convenient. It is invoked exactly once on service shutdown, even when stopAsync() is called multiple times.

When this method is called state() will return Service.State.STOPPING, which is the external state observable by the caller of stopAsync().

Since:

27.0

startAsync

@CanIgnoreReturnValue
public final Service startAsync()

Description copied from interface: Service

If the service state is Service.State.NEW, this initiates service startup and returns immediately. A stopped service may not be restarted.

Specified by:

startAsync in interface Service

Returns:

this

stopAsync

@CanIgnoreReturnValue
public final Service stopAsync()

Description copied from interface: Service

If the service is starting or running, this initiates service shutdown and returns immediately. If the service is new, it is terminated without having been started nor stopped. If the service has already been stopped, this method returns immediately without taking action.

Specified by:

stopAsync in interface Service

Returns:

this

awaitRunning

public final void awaitRunning()

Description copied from interface: Service

Waits for the Service to reach the running state.

Specified by:

awaitRunning in interface Service

awaitRunning

public final void awaitRunning(long timeout,
                               TimeUnit unit)
                        throws TimeoutException

Description copied from interface: Service

Waits for the Service to reach the running state for no more than the given time.

Specified by:

awaitRunning in interface Service

Parameters:

timeout - the maximum time to wait

unit - the time unit of the timeout argument

Throws:

TimeoutException - if the service has not reached the given state within the deadline

awaitTerminated

public final void awaitTerminated()

Description copied from interface: Service

Waits for the Service to reach the terminated state.

Specified by:

awaitTerminated in interface Service

awaitTerminated

public final void awaitTerminated(long timeout,
                                  TimeUnit unit)
                           throws TimeoutException

Description copied from interface: Service

Waits for the Service to reach a terminal state (either terminated or failed) for no more than the given time.

Specified by:

awaitTerminated in interface Service

Parameters:

timeout - the maximum time to wait

unit - the time unit of the timeout argument

Throws:

TimeoutException - if the service has not reached the given state within the deadline

notifyStarted

protected final void notifyStarted()

Implementing classes should invoke this method once their service has started. It will cause the service to transition from Service.State.STARTING to Service.State.RUNNING.

Throws:

IllegalStateException - if the service is not Service.State.STARTING.

notifyStopped

protected final void notifyStopped()

Implementing classes should invoke this method once their service has stopped. It will cause the service to transition from Service.State.STARTING or Service.State.STOPPING to Service.State.TERMINATED.

Throws:

IllegalStateException - if the service is not one of Service.State.STOPPING, Service.State.STARTING, or Service.State.RUNNING.

notifyFailed

protected final void notifyFailed(Throwable cause)

Invoke this method to transition the service to the Service.State.FAILED. The service will not be stopped if it is running. Invoke this method when a service has failed critically or otherwise cannot be started nor stopped.

isRunning

public final boolean isRunning()

Description copied from interface: Service

Returns true if this service is running.

Specified by:

isRunning in interface Service

state

public final Service.State state()

Description copied from interface: Service

Returns the lifecycle state of the service.

Specified by:

state in interface Service

failureCause

public final Throwable failureCause()

Description copied from interface: Service

Returns the Throwable that caused this service to fail.

Specified by:

failureCause in interface Service

Since:

14.0

addListener

public final void addListener(Service.Listener listener,
                              Executor executor)

Description copied from interface: Service

Registers a Service.Listener to be executed on the given executor. The listener will have the corresponding transition method called whenever the service changes state. The listener will not have previous state changes replayed, so it is suggested that listeners are added before the service starts.

addListener guarantees execution ordering across calls to a given listener but not across calls to multiple listeners. Specifically, a given listener will have its callbacks invoked in the same order as the underlying service enters those states. Additionally, at most one of the listener's callbacks will execute at once. However, multiple listeners' callbacks may execute concurrently, and listeners may execute in an order different from the one in which they were registered.

RuntimeExceptions thrown by a listener will be caught and logged. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException) will be caught and logged.

Specified by:

addListener in interface Service

Parameters:

listener - the listener to run when the service changes state is complete

executor - the executor in which the listeners callback methods will be run. For fast, lightweight listeners that would be safe to execute in any thread, consider MoreExecutors.directExecutor().

Since:

13.0

toString

public String toString()

Overrides:

toString in class Object