| /* |
| * 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.apache.felix.dm.impl; |
| |
| import java.util.concurrent.ConcurrentLinkedQueue; |
| import java.util.concurrent.Executor; |
| import java.util.concurrent.RejectedExecutionException; |
| import java.util.concurrent.atomic.AtomicBoolean; |
| |
| import org.apache.felix.dm.Logger; |
| import org.osgi.service.log.LogService; |
| |
| /** |
| * A DispatchExecutor is a queue that can execute FIFO tasks in a shared threadpool configured for the dispatcher. |
| * Each task scheduled in a given DispatchExecutor will be executed serially in FIFO order; and multiple |
| * DispatchExecutor instances may each run concurrently with respect to each other. |
| * <p> |
| * |
| * This class also supports synchronous scheduling, like the @link {@link SerialExecutor} class; and in this case, |
| * only one caller thread will execute the tasks scheduled in the DispatchQueue (and the internal |
| * threadpool won't be used). |
| * |
| * <p> |
| * |
| * This class is <b>lock free</b> by design and ensures <b>"safe object publication"</b> between scheduling threads and |
| * actual executing thread: if one thread T1 schedules a task, but another thread T2 actually |
| * executes it, then all the objects from the T1 thread will be "safely published" to the executing T2 thread. |
| * Safe publication is ensured because we are using a ConcurrentLinkedQueue, and volatile attributes. |
| * (see [1], chapter 3.5.3 (Safe publication idioms). |
| * |
| * [1] Java Concurrency In Practice, Addison Wesley |
| * |
| * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> |
| */ |
| public class DispatchExecutor implements Executor, Runnable { |
| /** |
| * The threadpool used for the execution of the tasks that are scheduled in this queue. |
| */ |
| private final Executor m_threadPool; |
| |
| /** |
| * List of tasks scheduled in our queue. |
| */ |
| protected final ConcurrentLinkedQueue<Runnable> m_tasks = new ConcurrentLinkedQueue<>(); |
| |
| /** |
| * Marker used to remember the id of the thread currently executing this dispatch queue. |
| */ |
| private volatile Thread m_executingThread; |
| |
| /** |
| * Flag telling if this dispatch queue is already scheduled for execution in the threadpool. |
| */ |
| private final AtomicBoolean m_scheduled = new AtomicBoolean(); |
| |
| /** |
| * Logger used to log exceptions thrown by scheduled tasks. |
| */ |
| private final Logger m_logger; |
| |
| /** |
| * Creates a new DispatchQueue, which can be executed within a fixed thread pool. Multiple queue |
| * can be executed concurrently, but all runnables scheduled in a given queue will be executed serially, |
| * in FIFO order. |
| * |
| * @param threadPool the executor (typically a threadpool) used to execute this DispatchExecutor. |
| * @param logger the Logger used when errors are taking place |
| */ |
| public DispatchExecutor(Executor threadPool, Logger logger) { |
| m_logger = logger; |
| m_threadPool = threadPool; |
| } |
| |
| /** |
| * Enqueues a task for later execution. You must call {@link #execute()} in order |
| * to trigger the actual execution of all scheduled tasks (in FIFO order). |
| */ |
| public void schedule(Runnable task) { |
| m_tasks.add(task); |
| } |
| |
| /** |
| * Submits a task in this queue, and schedule the execution of this DispatchQueue in the threadpool. |
| * The task is immediately executed (inline execution) if the queue is currently being executed by |
| * the current thread. |
| */ |
| public void execute(Runnable task) { |
| execute(task, true); |
| } |
| |
| /** |
| * Schedules a task in this queue. |
| * If the queue is currently being executed by the current thread, then the task is executed immediately. |
| * @tasks the task to schedule |
| * @threadpool true if the queue should be executed in the threadpool, false if the queue must be executed by |
| * only one caller thread. |
| */ |
| public void execute(Runnable task, boolean threadpool) { |
| Thread currThread = Thread.currentThread(); |
| if (m_executingThread == currThread) { |
| runTask(task); |
| } else { |
| schedule(task); |
| execute(threadpool); |
| } |
| } |
| |
| /** |
| * Schedules the execution of this DispatchQueue in the threadpool. |
| */ |
| public void execute() { |
| execute(true); |
| } |
| |
| /** |
| * Schedules the execution of this DispatchQueue in the threadpool, or from a single caller thread. |
| * |
| * @param threadpool true means the DispatchQueue is executed in the threadpool, false means the queue is executed from the |
| * caller thread. |
| */ |
| public void execute(boolean threadpool) { |
| if (m_scheduled.compareAndSet(false, true)) { // schedules our run method in the tpool. |
| try { |
| if (threadpool) { |
| m_threadPool.execute(this); |
| } else { |
| run(); // run all queue tasks from the caller thread |
| } |
| } catch (RejectedExecutionException e) { |
| // The threadpool seems stopped (maybe the framework is being stopped). Anyway, just execute our tasks |
| // from the current thread. |
| run(); |
| } |
| } |
| } |
| |
| /** |
| * Run all tasks scheduled in this queue, in FIFO order. This method may be executed either in the threadpool, or from |
| * the caller thread. |
| */ |
| @Override |
| public void run() { |
| try { |
| // We do a memory barrier in order to ensure consistent per-thread |
| // memory visibility |
| m_executingThread = Thread.currentThread(); |
| Runnable task; |
| while ((task = m_tasks.poll()) != null) { |
| runTask(task); |
| } |
| } finally { |
| m_scheduled.set(false); |
| m_executingThread = null; |
| if (m_tasks.peek() != null) { |
| execute(); |
| } |
| } |
| } |
| |
| /** |
| * Runs a given task |
| * @param task the task to execute |
| */ |
| private void runTask(Runnable task) { |
| try { |
| task.run(); |
| } catch (Throwable t) { |
| m_logger.log(LogService.LOG_ERROR, "Error processing tasks", t); |
| } |
| } |
| } |