Added back the ParallelProcessor, cleaned and simplified, and without any dependencies.
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171
src/dorkbox/util/ParallelProcessor.java
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171
src/dorkbox/util/ParallelProcessor.java
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/*
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* Copyright 2015 dorkbox, llc
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package dorkbox.util;
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import java.util.ArrayList;
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import java.util.concurrent.ArrayBlockingQueue;
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import java.util.concurrent.CountDownLatch;
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import org.slf4j.Logger;
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/**
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* A utility class to simplify processing data/work/tasks on multiple threads.
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* <p>
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* Remember that the JMM requires that empty 'synchronize' will not be optimized out by the compiler or JIT!
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* <p>
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* This isn't the FASTEST implementation, but it is relatively easy and solid. Also minimal GC through object pools
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*/
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@SuppressWarnings({"unused", "WeakerAccess"})
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public abstract
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class ParallelProcessor<T extends Runnable> {
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private static final Object SENTINEL = new Object[0];
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private final ArrayBlockingQueue<T> workerPool;
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private final ArrayList<Thread> threads;
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private final ArrayBlockingQueue<Object> queue;
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private final CountDownLatch latch;
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public
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ParallelProcessor() {
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this(OS.getOptimumNumberOfThreads(), null);
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}
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public
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ParallelProcessor(final int numberOfThreads, final Logger logger) {
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latch = new CountDownLatch(numberOfThreads);
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workerPool = new ArrayBlockingQueue<T>(numberOfThreads);
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for (int i = 0; i < numberOfThreads; i++) {
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T e = createWorker();
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this.workerPool.add(e);
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}
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queue = new ArrayBlockingQueue<Object>(numberOfThreads * 2);
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threads = new ArrayList<Thread>(numberOfThreads);
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ThreadGroup threadGroup = new ThreadGroup(Thread.currentThread()
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.getThreadGroup(), "ParallelProcessor");
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NamedThreadFactory dispatchThreadFactory = new NamedThreadFactory("Processor", threadGroup);
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for (int i = 0; i < numberOfThreads; i++) {
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Runnable runnable = new Runnable() {
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@SuppressWarnings("unchecked")
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@Override
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public
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void run() {
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ArrayBlockingQueue<Object> queue = ParallelProcessor.this.queue;
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Object taken = null;
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while (true) {
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// we want to continue, even if there is an error (until we decide to shutdown).
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try {
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taken = queue.take();
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// only two types, the sentinel or the work to be done
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if (taken == SENTINEL) {
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latch.countDown();
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return;
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}
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T work = (T) taken;
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// this does the work, and stores the result
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work.run();
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workComplete(work);
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} catch (Throwable t) {
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if (logger != null) {
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logger.error("Error during execution of work!", t.getMessage());
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}
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else {
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String message = t.getMessage();
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int index = message.indexOf(OS.LINE_SEPARATOR);
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if (index > -1) {
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message = message.substring(0, index);
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}
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System.err.println("Error during execution of work! " + message);
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}
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} finally {
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if (taken instanceof Runnable) {
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// Return object to the pool, waking the threads that have blocked during take()
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ParallelProcessor.this.workerPool.offer((T) taken);
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}
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}
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}
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}
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};
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Thread runner = dispatchThreadFactory.newThread(runnable);
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this.threads.add(runner);
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}
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for (Thread thread : threads) {
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thread.start();
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}
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}
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/**
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* Creates a worker to be placed into the worker pool. This is only called when necessary.
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*/
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public abstract
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T createWorker();
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/**
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* Called each time a single piece of work (a task) is completed.
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*/
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public abstract
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void workComplete(T worker);
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public
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ParallelProcessor(final int numberOfThreads) {
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this(numberOfThreads, null);
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}
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/**
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* Gets the next available worker, blocks until a worker is available.
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*
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* @throws InterruptedException if the current thread is interrupted while waiting
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*/
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public
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T nextWorker() throws InterruptedException {
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return this.workerPool.take();
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}
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/**
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* Queues task to be completed
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*
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* @throws InterruptedException if the current thread is interrupted while waiting
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*/
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public
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void queueTask(final T work) throws InterruptedException {
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queue.put(work);
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}
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/**
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* Waits for the results to finish processing. No more work should be queued after this is called.
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*
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* @throws InterruptedException if the current thread is interrupted while waiting
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*/
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public
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void waitUntilDone() throws InterruptedException {
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for (int i = 0; i < threads.size(); i++) {
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// this tells out threads that we have finished work and can exit
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queue.put(SENTINEL);
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}
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latch.await();
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}
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}
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