@Beta 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.
Service.Listener, Service.State| Modifier | Constructor and Description |
|---|---|
protected |
AbstractService()
Constructor for use by subclasses.
|
| 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. |
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()
|
String |
toString() |
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.
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.
public final Service startAsync()
ServiceIf the service state is Service.State.NEW, this initiates service startup and returns immediately. A stopped service may not be restarted.
startAsync in interface Servicepublic final Service stopAsync()
ServiceIf 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.
public final void awaitRunning()
ServiceWaits for the Service to reach the running state.
awaitRunning in interface Servicepublic final void awaitRunning(long timeout,
TimeUnit unit)
throws TimeoutException
ServiceWaits for the Service to reach the running state for no more than the given time.
awaitRunning in interface Servicetimeout - the maximum time to waitunit - the time unit of the timeout argumentTimeoutException - if the service has not reached the given state within the deadlinepublic final void awaitTerminated()
ServiceWaits for the Service to reach the terminated state.
awaitTerminated in interface Servicepublic final void awaitTerminated(long timeout,
TimeUnit unit)
throws TimeoutException
ServiceWaits for the Service to reach a terminal state (either terminated or failed) for no more than the given time.
awaitTerminated in interface Servicetimeout - the maximum time to waitunit - the time unit of the timeout argumentTimeoutException - if the service has not reached the given state within the deadlineprotected 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.
IllegalStateException - if the service is not Service.State.STARTING.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.STOPPING to Service.State.TERMINATED.
IllegalStateException - if the service is neither Service.State.STOPPING nor Service.State.RUNNING.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.
public final boolean isRunning()
ServiceReturns true if this service is running.
public final Service.State state()
ServiceReturns the lifecycle state of the service.
public final Throwable failureCause()
ServiceReturns the Throwable that caused this service to fail.
failureCause in interface Servicepublic final void addListener(Service.Listener listener, Executor executor)
ServiceRegisters 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.
addListener in interface Servicelistener - 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, consider MoreExecutors.directExecutor().