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:

• Service.State.NEW ->
• Service.State.STARTING ->
• Service.State.RUNNING ->
• Service.State.STOPPING ->
• Service.State.TERMINATED

The valid state transitions of a Service are:

• Service.State.NEW -> Service.State.STARTING: This occurs when start() is called the first time and is the only valid state transition from the NEW state.
• Service.State.NEW -> Service.State.TERMINATED: This occurs when stop() is called from the NEW state.
• Service.State.STARTING -> Service.State.RUNNING: This occurs when a service has successfully started
• Service.State.STARTING -> Service.State.FAILED: This occurs when a service experiences an unrecoverable error while starting up
• Service.State.STARTING -> Service.State.STOPPING: This occurs when stop() is called while a service is starting up.
• Service.State.RUNNING -> Service.State.STOPPING: This occurs when stop() is called on a running service.
• Service.State.RUNNING -> Service.State.FAILED: This occurs when an unrecoverable error occurs while a service is running.
• Service.State.STOPPING -> Service.State.FAILED: This occurs when an unrecoverable error occurs while a service is stopping.
• Service.State.STOPPING -> Service.State.TERMINATED: This occurs when the service successfully stops.

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

Nested Class Summary

static class

Service.State The lifecycle states of a service.

Method Summary

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 shutdown failed