/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.foo.log;
import org.osgi.framework.*;
import org.osgi.service.log.LogService;
/**
* Broken code example showing why you shouldn't store a service instance in a
* long-lived variable like a field. Firstly you can't tell if the service has
* been removed, and should not be used anymore. Secondly the strong reference
* to the instance will stop it from being GC'd until the client is GC'd which
* could be a long time after the original service bundle is uninstalled.
**/
public class Activator implements BundleActivator {
LogService m_logService;
/**
* START LOG TEST
**/
public void start(BundleContext context) {
// find a single LogService service - notice the refactor-friendly use of Class.getName()
ServiceReference logServiceRef = context.getServiceReference(LogService.class.getName());
// dereference handle to get the service instance and store it in a field (not a good idea)
m_logService = (LogService) context.getService(logServiceRef);
// start new thread to test LogService - remember to keep bundle activator methods short!
startTestThread();
}
/**
* STOP LOG TEST
**/
public void stop(BundleContext context) {
stopTestThread();
}
// Test LogService by periodically sending a message
class LogServiceTest implements Runnable {
public void run() {
while (Thread.currentThread() == m_logTestThread) {
m_logService.log(LogService.LOG_INFO, "ping");
pauseTestThread();
}
}
}
//------------------------------------------------------------------------------------------
// The rest of this is just support code, not meant to show any particular best practices
//------------------------------------------------------------------------------------------
volatile Thread m_logTestThread;
void startTestThread() {
// start separate worker thread to run the actual tests, managed by the bundle lifecycle
m_logTestThread = new Thread(new LogServiceTest(), "LogService Tester");
m_logTestThread.setDaemon(true);
m_logTestThread.start();
}
void stopTestThread() {
// thread should cooperatively shutdown on the next iteration, because field is now null
Thread testThread = m_logTestThread;
m_logTestThread = null;
if (testThread != null) {
testThread.interrupt();
try {testThread.join();} catch (InterruptedException e) {}
}
}
void pauseTestThread() {
try {
// sleep for a bit
Thread.sleep(5000);
} catch (InterruptedException e) {}
}
}