Interface Service
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- All Known Implementing Classes:
AbstractExecutionThreadService
,AbstractIdleService
,AbstractScheduledService
,AbstractService
@DoNotMock("Create an AbstractIdleService") @GwtIncompatible public interface Service
An object with an operational state, plus asynchronousstartAsync()
andstopAsync()
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 theService
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. TheService.State.FAILED
andService.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
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Nested Class Summary
Nested Classes Modifier and Type Interface Description static class
Service.Listener
A listener for the various state changes that aService
goes through in its lifecycle.static class
Service.State
The lifecycle states of a service.
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description void
addListener(Service.Listener listener, java.util.concurrent.Executor executor)
Registers aService.Listener
to be executed on the given executor.void
awaitRunning()
Waits for theService
to reach the running state.void
awaitRunning(long timeout, java.util.concurrent.TimeUnit unit)
Waits for theService
to reach the running state for no more than the given time.void
awaitTerminated()
Waits for theService
to reach the terminated state.void
awaitTerminated(long timeout, java.util.concurrent.TimeUnit unit)
Waits for theService
to reach a terminal state (eitherterminated
orfailed
) for no more than the given time.java.lang.Throwable
failureCause()
Returns theThrowable
that caused this service to fail.boolean
isRunning()
Returnstrue
if this service is running.Service
startAsync()
If the service state isService.State.NEW
, this initiates service startup and returns immediately.Service.State
state()
Returns the lifecycle state of the service.Service
stopAsync()
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Method Detail
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startAsync
@CanIgnoreReturnValue Service startAsync()
If the service state isService.State.NEW
, this initiates service startup and returns immediately. A stopped service may not be restarted.- Returns:
- this
- Throws:
java.lang.IllegalStateException
- if the service is notService.State.NEW
- Since:
- 15.0
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state
Service.State state()
Returns the lifecycle state of the service.
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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
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awaitRunning
void awaitRunning()
Waits for theService
to reach the running state.- Throws:
java.lang.IllegalStateException
- if the service reaches a state from which it is not possible to enter theService.State.RUNNING
state. e.g. if thestate
isState#TERMINATED
when this method is called then this will throw an IllegalStateException.- Since:
- 15.0
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awaitRunning
void awaitRunning(long timeout, java.util.concurrent.TimeUnit unit) throws java.util.concurrent.TimeoutException
Waits for theService
to reach the running state for no more than the given time.- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Throws:
java.util.concurrent.TimeoutException
- if the service has not reached the given state within the deadlinejava.lang.IllegalStateException
- if the service reaches a state from which it is not possible to enter theRUNNING
state. e.g. if thestate
isState#TERMINATED
when this method is called then this will throw an IllegalStateException.- Since:
- 15.0
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awaitTerminated
void awaitTerminated()
Waits for theService
to reach the terminated state.- Throws:
java.lang.IllegalStateException
- if the service fails.- Since:
- 15.0
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awaitTerminated
void awaitTerminated(long timeout, java.util.concurrent.TimeUnit unit) throws java.util.concurrent.TimeoutException
Waits for theService
to reach a terminal state (eitherterminated
orfailed
) for no more than the given time.- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Throws:
java.util.concurrent.TimeoutException
- if the service has not reached the given state within the deadlinejava.lang.IllegalStateException
- if the service fails.- Since:
- 15.0
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failureCause
java.lang.Throwable failureCause()
Returns theThrowable
that caused this service to fail.- Throws:
java.lang.IllegalStateException
- if this service's state isn't FAILED.- Since:
- 14.0
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addListener
void addListener(Service.Listener listener, java.util.concurrent.Executor executor)
Registers aService.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., aRejectedExecutionException
) will be caught and logged.- Parameters:
listener
- the listener to run when the service changes state is completeexecutor
- the executor in which the listeners callback methods will be run. For fast, lightweight listeners that would be safe to execute in any thread, considerMoreExecutors.directExecutor()
.- Since:
- 13.0
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