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/*
* Copyright (C) 2009 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.util.concurrent;
import com.google.common.annotations.Beta;
import com.google.common.base.Throwables;
import java.util.concurrent.Executor;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Base class for services that can implement {@link #startUp}, {@link #run} and
* {@link #shutDown} methods. This class uses a single thread to execute the
* service; consider {@link AbstractService} if you would like to manage any
* threading manually.
*
* @author Jesse Wilson
* @since 1.0
*/
@Beta
public abstract class AbstractExecutionThreadService implements Service {
private static final Logger logger = Logger.getLogger(
AbstractExecutionThreadService.class.getName());
/* use AbstractService for state management */
private final Service delegate = new AbstractService() {
@Override protected final void doStart() {
executor().execute(new Runnable() {
@Override
public void run() {
try {
startUp();
notifyStarted();
if (isRunning()) {
try {
AbstractExecutionThreadService.this.run();
} catch (Throwable t) {
try {
shutDown();
} catch (Exception ignored) {
logger.log(Level.WARNING,
"Error while attempting to shut down the service"
+ " after failure.", ignored);
}
throw t;
}
}
shutDown();
notifyStopped();
} catch (Throwable t) {
notifyFailed(t);
throw Throwables.propagate(t);
}
}
});
}
@Override protected void doStop() {
triggerShutdown();
}
};
/**
* Constructor for use by subclasses.
*/
protected AbstractExecutionThreadService() {}
/**
* Start the service. This method is invoked on the execution thread.
*
* <p>By default this method does nothing.
*/
protected void startUp() throws Exception {}
/**
* Run the service. This method is invoked on the execution thread.
* Implementations must respond to stop requests. You could poll for lifecycle
* changes in a work loop:
* <pre>
* public void run() {
* while ({@link #isRunning()}) {
* // perform a unit of work
* }
* }
* </pre>
* ...or you could respond to stop requests by implementing {@link
* #triggerShutdown()}, which should cause {@link #run()} to return.
*/
protected abstract void run() throws Exception;
/**
* Stop the service. This method is invoked on the execution thread.
*
* <p>By default this method does nothing.
*/
// TODO: consider supporting a TearDownTestCase-like API
protected void shutDown() throws Exception {}
/**
* Invoked to request the service to stop.
*
* <p>By default this method does nothing.
*/
protected void triggerShutdown() {}
/**
* Returns the {@link Executor} that will be used to run this service.
* Subclasses may override this method to use a custom {@link Executor}, which
* may configure its worker thread with a specific name, thread group or
* priority. The returned executor's {@link Executor#execute(Runnable)
* execute()} method is called when this service is started, and should return
* promptly.
*
* <p>The default implementation returns a new {@link Executor} that sets the
* name of its threads to the string returned by {@link #serviceName}
*/
protected Executor executor() {
return new Executor() {
@Override
public void execute(Runnable command) {
MoreExecutors.newThread(serviceName(), command).start();
}
};
}
@Override public String toString() {
return serviceName() + " [" + state() + "]";
}
// We override instead of using ForwardingService so that these can be final.
@Override public final ListenableFuture<State> start() {
return delegate.start();
}
@Override public final State startAndWait() {
return delegate.startAndWait();
}
@Override public final boolean isRunning() {
return delegate.isRunning();
}
@Override public final State state() {
return delegate.state();
}
@Override public final ListenableFuture<State> stop() {
return delegate.stop();
}
@Override public final State stopAndWait() {
return delegate.stopAndWait();
}
/**
* @since 13.0
*/
@Override public final void addListener(Listener listener, Executor executor) {
delegate.addListener(listener, executor);
}
/**
* @since 14.0
*/
@Override public final Throwable failureCause() {
return delegate.failureCause();
}
/**
* Returns the name of this service. {@link AbstractExecutionThreadService}
* may include the name in debugging output.
*
* <p>Subclasses may override this method.
*
* @since 14.0 (present in 10.0 as getServiceName)
*/
protected String serviceName() {
return getClass().getSimpleName();
}
}
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