com.google.common.util.concurrent

Interface Service

All Known Implementing Classes:

AbstractExecutionThreadService, AbstractIdleService, AbstractScheduledService, AbstractService

@Beta
 @GwtIncompatible
public interface Service

An object with an operational state, plus asynchronous startAsync() and stopAsync() 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 stopAsync() 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 class	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

Modifier and Type	Method and 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.
Throwable	failureCause() Returns the Throwable that caused this service to fail.
boolean	isRunning() Returns true if this service is running.
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.

Method Detail

startAsync

@CanIgnoreReturnValue
Service startAsync()

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

Returns:

this

Throws:

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

Since:

15.0

isRunning

boolean isRunning()

Returns true if this service is running.

state

Service.State state()

Returns the lifecycle state of the service.

stopAsync

@CanIgnoreReturnValue
Service stopAsync()

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:

this

Since:

15.0

awaitRunning

void awaitRunning()

Waits for the Service to reach the running state.

Throws:

IllegalStateException - if the service reaches a state from which it is not possible to enter the Service.State.RUNNING state. e.g. if the state is State#TERMINATED when this method is called then this will throw an IllegalStateException.

Since:

15.0

awaitRunning

void awaitRunning(long timeout,
                  TimeUnit unit)
           throws TimeoutException

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

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

IllegalStateException - if the service reaches a state from which it is not possible to enter the RUNNING state. e.g. if the state is State#TERMINATED when this method is called then this will throw an IllegalStateException.

Since:

15.0

awaitTerminated

void awaitTerminated()

Waits for the Service to reach the terminated state.

Throws:

IllegalStateException - if the service fails.

Since:

15.0

awaitTerminated

void awaitTerminated(long timeout,
                     TimeUnit unit)
              throws TimeoutException

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

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

IllegalStateException - if the service fails.

Since:

15.0

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.

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.

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