com.google.common.util.concurrent

Interface Service

All Known Implementing Classes:

AbstractExecutionThreadService, AbstractIdleService, AbstractScheduledService, AbstractService, ForwardingService

@Beta
public interface Service

An object with an operational state, plus asynchronous start() and stop() lifecycle methods to transition between states. Example services include webservers, RPC servers and timers.

The normal lifecycle of a service is:

• NEW ->
• STARTING ->
• RUNNING ->
• STOPPING ->
• TERMINATED

There are deviations from this if there are failures or if stop() is called before the Service reaches the RUNNING state. The set of legal transitions form a DAG, therefore every method of the listener will be called at most once. N.B. The Service.State.FAILED and Service.State.TERMINATED states are terminal states, once a service enters either of these states it cannot ever leave them.

Implementors of this interface are strongly encouraged to extend one of the abstract classes in this package which implement this interface and make the threading and state management easier.

Since:

9.0 (in 1.0 as com.google.common.base.Service)

Author:

Jesse Wilson, Luke Sandberg

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	Service.Listener A listener for the various state changes that a Service goes through in its lifecycle.
static class	Service.State The lifecycle states of a service.

Method Summary

Methods

Modifier and Type	Method and Description
void	addListener(Service.Listener listener, Executor executor) Registers a Service.Listener to be executed on the given executor.
Throwable	failureCause() Returns the Throwable that caused this service to fail.
boolean	isRunning() Returns true if this service is running.
ListenableFuture<Service.State>	start() If the service state is Service.State.NEW, this initiates service startup and returns immediately.
Service.State	startAndWait() Initiates service startup (if necessary), returning once the service has finished starting.
Service.State	state() Returns the lifecycle state of the service.
ListenableFuture<Service.State>	stop() If the service is starting or running, this initiates service shutdown and returns immediately.
Service.State	stopAndWait() Initiates service shutdown (if necessary), returning once the service has finished stopping.

Method Detail

start

ListenableFuture<Service.State> start()

If the service state is Service.State.NEW, this initiates service startup and returns immediately. If the service has already been started, this method returns immediately without taking action. A stopped service may not be restarted.

Returns:

a future for the startup result, regardless of whether this call initiated startup. Calling Future.get() will block until the service has finished starting, and returns one of Service.State.RUNNING, Service.State.STOPPING or Service.State.TERMINATED. If the service fails to start, Future.get() will throw an ExecutionException, and the service's state will be Service.State.FAILED. If it has already finished starting, Future.get() returns immediately. Cancelling this future has no effect on the service.

startAndWait

Service.State startAndWait()

Initiates service startup (if necessary), returning once the service has finished starting. Unlike calling start().get(), this method throws no checked exceptions, and it cannot be interrupted.

Returns:

the state of the service when startup finished.

Throws:

UncheckedExecutionException - if startup failed

isRunning

boolean isRunning()

Returns true if this service is running.

state

Service.State state()

Returns the lifecycle state of the service.

stop

ListenableFuture<Service.State> stop()

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.

Returns:

a future for the shutdown result, regardless of whether this call initiated shutdown. Calling Future.get() will block until the service has finished shutting down, and either returns Service.State.TERMINATED or throws an ExecutionException. If it has already finished stopping, Future.get() returns immediately. Cancelling this future has no effect on the service.

stopAndWait

Service.State stopAndWait()

Initiates service shutdown (if necessary), returning once the service has finished stopping. If this is Service.State.STARTING, startup will be cancelled. If this is Service.State.NEW, it is terminated without having been started nor stopped. Unlike calling stop().get(), this method throws no checked exceptions.

Returns:

the state of the service when shutdown finished.

Throws:

UncheckedExecutionException - if the service has failed or fails during shutdown

failureCause

Throwable failureCause()

Returns the Throwable that caused this service to fail.

Throws:

IllegalStateException - if this service's state isn't FAILED.

Since:

14.0

addListener

void addListener(Service.Listener listener,
               Executor executor)

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.

There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called whenever there is a state change.

Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException or an exception thrown by inline execution) will be caught and logged.

Parameters:

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

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

Since:

13.0