Class AbstractScheduledService
- java.lang.Object
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- com.google.common.util.concurrent.AbstractScheduledService
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- All Implemented Interfaces:
Service
@GwtIncompatible public abstract class AbstractScheduledService extends Object implements Service
Base class for services that can implementstartUp()
andshutDown()
but while in the "running" state need to perform a periodic task. Subclasses can implementstartUp()
,shutDown()
and also arunOneIteration()
method that will be executed periodically.This class uses the
ScheduledExecutorService
returned fromexecutor()
to run thestartUp()
andshutDown()
methods and also uses that service to schedule therunOneIteration()
that will be executed periodically as specified by itsAbstractScheduledService.Scheduler
. When this service is asked to stop viastopAsync()
it will cancel the periodic task (but not interrupt it) and wait for it to stop before running theshutDown()
method.Subclasses are guaranteed that the life cycle methods (
runOneIteration()
,startUp()
andshutDown()
) will never run concurrently. Notably, if any execution ofrunOneIteration()
takes longer than its schedule defines, then subsequent executions may start late. Also, all life cycle methods are executed with a lock held, so subclasses can safely modify shared state without additional synchronization necessary for visibility to later executions of the life cycle methods.Usage Example
Here is a sketch of a service which crawls a website and uses the scheduling capabilities to rate limit itself.
class CrawlingService extends AbstractScheduledService { private Set<Uri> visited; private Queue<Uri> toCrawl; protected void startUp() throws Exception { toCrawl = readStartingUris(); } protected void runOneIteration() throws Exception { Uri uri = toCrawl.remove(); Collection<Uri> newUris = crawl(uri); visited.add(uri); for (Uri newUri : newUris) { if (!visited.contains(newUri)) { toCrawl.add(newUri); } } } protected void shutDown() throws Exception { saveUris(toCrawl); } protected Scheduler scheduler() { return Scheduler.newFixedRateSchedule(0, 1, TimeUnit.SECONDS); } }
This class uses the life cycle methods to read in a list of starting URIs and save the set of outstanding URIs when shutting down. Also, it takes advantage of the scheduling functionality to rate limit the number of queries we perform.
- Since:
- 11.0
- Author:
- Luke Sandberg
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
AbstractScheduledService.CustomScheduler
AAbstractScheduledService.Scheduler
that provides a convenient way for theAbstractScheduledService
to use a dynamically changing schedule.static class
AbstractScheduledService.Scheduler
A scheduler defines the policy for how theAbstractScheduledService
should run its task.-
Nested classes/interfaces inherited from interface com.google.common.util.concurrent.Service
Service.Listener, Service.State
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Constructor Summary
Constructors Modifier Constructor Description protected
AbstractScheduledService()
Constructor for use by subclasses.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description void
addListener(Service.Listener listener, 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, 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, TimeUnit unit)
Waits for theService
to reach a terminal state (eitherterminated
orfailed
) for no more than the given time.protected ScheduledExecutorService
executor()
Returns theScheduledExecutorService
that will be used to execute thestartUp()
,runOneIteration()
andshutDown()
methods.Throwable
failureCause()
Returns theThrowable
that caused this service to fail.boolean
isRunning()
Returnstrue
if this service is running.protected abstract void
runOneIteration()
Run one iteration of the scheduled task.protected abstract AbstractScheduledService.Scheduler
scheduler()
Returns theAbstractScheduledService.Scheduler
object used to configure this service.protected String
serviceName()
Returns the name of this service.protected void
shutDown()
Stop the service.Service
startAsync()
If the service state isService.State.NEW
, this initiates service startup and returns immediately.protected void
startUp()
Start the service.Service.State
state()
Returns the lifecycle state of the service.Service
stopAsync()
String
toString()
Returns a string representation of the object.
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Constructor Detail
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AbstractScheduledService
protected AbstractScheduledService()
Constructor for use by subclasses.
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Method Detail
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runOneIteration
protected abstract void runOneIteration() throws Exception
Run one iteration of the scheduled task. If any invocation of this method throws an exception, the service will transition to theService.State.FAILED
state and this method will no longer be called.- Throws:
Exception
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startUp
protected void startUp() throws Exception
Start the service.By default this method does nothing.
- Throws:
Exception
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shutDown
protected void shutDown() throws Exception
Stop the service. This is guaranteed not to run concurrently withrunOneIteration()
.By default this method does nothing.
- Throws:
Exception
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scheduler
protected abstract AbstractScheduledService.Scheduler scheduler()
Returns theAbstractScheduledService.Scheduler
object used to configure this service. This method will only be called once.
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executor
protected ScheduledExecutorService executor()
Returns theScheduledExecutorService
that will be used to execute thestartUp()
,runOneIteration()
andshutDown()
methods. If this method is overridden the executor will not be shutdown when this service terminates or fails. Subclasses may override this method to supply a customScheduledExecutorService
instance. This method is guaranteed to only be called once.By default this returns a new
ScheduledExecutorService
with a single thread thread pool that sets the name of the thread to the service name. Also, the pool will be shut down when the service terminates or fails.
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serviceName
protected String serviceName()
Returns the name of this service.AbstractScheduledService
may include the name in debugging output.- Since:
- 14.0
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toString
public String toString()
Description copied from class:java.lang.Object
Returns a string representation of the object. In general, thetoString
method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.The
toString
method for classObject
returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@
', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:getClass().getName() + '@' + Integer.toHexString(hashCode())
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isRunning
public final boolean isRunning()
Description copied from interface:Service
Returnstrue
if this service is running.
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state
public final Service.State state()
Description copied from interface:Service
Returns the lifecycle state of the service.
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addListener
public final void addListener(Service.Listener listener, Executor executor)
Description copied from interface:Service
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.- Specified by:
addListener
in interfaceService
- 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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failureCause
public final Throwable failureCause()
Description copied from interface:Service
Returns theThrowable
that caused this service to fail.- Specified by:
failureCause
in interfaceService
- Since:
- 14.0
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startAsync
@CanIgnoreReturnValue public final Service startAsync()
Description copied from interface:Service
If the service state isService.State.NEW
, this initiates service startup and returns immediately. A stopped service may not be restarted.- Specified by:
startAsync
in interfaceService
- Returns:
- this
- Since:
- 15.0
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stopAsync
@CanIgnoreReturnValue public final Service stopAsync()
Description copied from interface:Service
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.
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awaitRunning
public final void awaitRunning()
Description copied from interface:Service
Waits for theService
to reach the running state.- Specified by:
awaitRunning
in interfaceService
- Since:
- 15.0
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awaitRunning
public final void awaitRunning(long timeout, TimeUnit unit) throws TimeoutException
Description copied from interface:Service
Waits for theService
to reach the running state for no more than the given time.- Specified by:
awaitRunning
in interfaceService
- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Throws:
TimeoutException
- if the service has not reached the given state within the deadline- Since:
- 15.0
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awaitTerminated
public final void awaitTerminated()
Description copied from interface:Service
Waits for theService
to reach the terminated state.- Specified by:
awaitTerminated
in interfaceService
- Since:
- 15.0
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awaitTerminated
public final void awaitTerminated(long timeout, TimeUnit unit) throws TimeoutException
Description copied from interface:Service
Waits for theService
to reach a terminal state (eitherterminated
orfailed
) for no more than the given time.- Specified by:
awaitTerminated
in interfaceService
- Parameters:
timeout
- the maximum time to waitunit
- the time unit of the timeout argument- Throws:
TimeoutException
- if the service has not reached the given state within the deadline- Since:
- 15.0
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