Updated the parallel processor to take in tasks (instead of a runnable). This make it a lot more simple/logical to use.
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@ -23,76 +23,136 @@ import java.util.concurrent.atomic.AtomicInteger;
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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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* A Parallel processor to simplify processing data on multiple threads and provide back-pressure to the main thread (that
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* creates the processor and adds work to it), so that memory is constrained at the expense of CPU waiting
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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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* This is NOT the FASTEST implementation, but it is relatively easy and solid.
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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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class ParallelProcessor<Task> {
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public
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interface Worker<Task> {
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/**
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* Runs the work.
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*
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* @return true if there was work done, otherwise false.
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*/
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boolean process(Task objectToProcess);
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}
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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 int numberOfThreads;
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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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private int totalWorkload = 0;
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private AtomicInteger currentProgress = new AtomicInteger(0);
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private final int totalWorkload;
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private final AtomicInteger currentProgress = new AtomicInteger(0);
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/**
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* Creates a Parallel processor to simplify processing data on multiple threads and provide back-pressure to the main thread (that
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* creates the processor and adds work to it), so that memory is constrained at the expense of CPU waiting
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* <p>
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* This will not track the progress from (0-1) but instead will record the total number of processed tasks
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* This will use the OS optimum number of threads (based on the CPU core count)
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* This will not assign a logger and errors will be printed to std.err
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*/
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public
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ParallelProcessor() {
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this(OS.getOptimumNumberOfThreads(), null);
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this(-1, OS.getOptimumNumberOfThreads(), null);
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}
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/**
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* Creates a Parallel processor to simplify processing data on multiple threads.
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* <p>
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* This implementation will provide back-pressure to the main thread (that creates the processor and adds work to it), so
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* that memory is constrained at the expense of CPU waiting
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*
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* This will use the OS optimum number of threads (based on the CPU core count)
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* This will not assign a logger and errors will be printed to std.err
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*
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* @param totalWorkload this is the total number of elements that need to be processed. -1 to disable
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*/
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public
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ParallelProcessor(final int numberOfThreads) {
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this(numberOfThreads, null);
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ParallelProcessor(final int totalWorkload) {
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this(totalWorkload, OS.getOptimumNumberOfThreads(), null);
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}
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/**
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* Creates a Parallel processor to simplify processing data on multiple threads.
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* <p>
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* This implementation will provide back-pressure to the main thread (that creates the processor and adds work to it), so
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* that memory is constrained at the expense of CPU waiting
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*
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* This will not assign a logger and errors will be printed to std.err
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*
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* @param totalWorkload this is the total number of elements that need to be processed. -1 to disable
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* @param numberOfThreads this is the number of threads requested to do the work
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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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ParallelProcessor(final int totalWorkload, final int numberOfThreads) {
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this(totalWorkload, numberOfThreads, null);
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}
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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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/**
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* Creates a Parallel processor to simplify processing data on multiple threads.
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* <p>
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* This implementation will provide back-pressure to the main thread (that creates the processor and adds work to it), so
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* that memory is constrained at the expense of CPU waiting
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*
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* @param totalWorkload this is the total number of elements that need to be processed. -1 to disable
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* @param numberOfThreads this is the number of threads requested to do the work
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* @param logger this is the logger to report errors (can be null)
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*/
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public
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ParallelProcessor(final int totalWorkload, final int numberOfThreads, final Logger logger) {
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this.totalWorkload = totalWorkload;
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this.numberOfThreads = numberOfThreads;
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latch = new CountDownLatch(this.numberOfThreads);
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queue = new ArrayBlockingQueue<Object>(numberOfThreads);
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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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java.lang.Runnable runnable = new java.lang.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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final ParallelProcessor<Task> processor = ParallelProcessor.this;
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final ArrayBlockingQueue<Object> queue = processor.queue;
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final Worker worker = createWorker();
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Object taken = null;
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Object taken;
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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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} catch (Throwable ignored) {
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// this thread was interrupted. Shouldn't ever really happen.
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return;
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}
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T work = (T) taken;
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Task task = (Task) 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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try {
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// this does the work
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worker.process(task);
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workComplete(ParallelProcessor.this, task);
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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);
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@ -101,17 +161,18 @@ class ParallelProcessor<T extends Runnable> {
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t.printStackTrace();
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}
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} finally {
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if (taken instanceof Runnable) {
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currentProgress.getAndIncrement();
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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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// record how much work was done
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currentProgress.getAndIncrement();
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// notify all threads that are waiting for processing to finish
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synchronized (currentProgress) {
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currentProgress.notifyAll();
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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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@ -122,89 +183,72 @@ class ParallelProcessor<T extends Runnable> {
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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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* Creates a worker which will perform work.
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*/
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public abstract
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T createWorker();
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Worker 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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void workComplete(ParallelProcessor processor, Task task);
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/**
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* Returns true if there are workers immediately available for work.
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* Returns true if there are workers immediately able to do work.
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*/
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public
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boolean hasAvailableWorker() {
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return !this.workerPool.isEmpty();
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return this.queue.size() < numberOfThreads;
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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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* Queues task to be worked on
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*
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* @throws InterruptedException if the current thread is interrupted while waiting
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* @throws InterruptedException if the current thread is interrupted while waiting for a worker to process the task
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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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void process(final Task taskToProcess) throws InterruptedException {
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queue.put(taskToProcess);
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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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* Notifies the threads that no more work will 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 doneQueueingTasks() throws InterruptedException {
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for (int i = 0; i < threads.size(); i++) {
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// this tells our threads that we have finished work and can exit
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queue.put(SENTINEL);
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}
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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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* Waits for the results to finish processing. No more work can be done 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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doneQueueingTasks();
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if (totalWorkload > 0) {
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while (currentProgress.get() - totalWorkload != 0) {
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synchronized (currentProgress) {
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currentProgress.wait(10000L); // waits 10 seconds
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}
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}
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}
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// stop all workers.
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for (int i = 0; i < threads.size(); i++) {
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// this tells our 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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* Sets the total amount of work to be performed. Also resets the count for the amount of work done.
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*/
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public
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void setTotalWorkload(int totalWorkload) {
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currentProgress.set(0);
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this.totalWorkload = totalWorkload;
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}
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/**
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* Gets the amount of progress made, between 0-1
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* Gets the amount of progress made, between 0-1 OR return the number of tasks completed (if called with totalWorkload = -1).
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* <p>
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* If this returns 0, it is safe to call {@link ParallelProcessor#waitUntilDone()}. It will block, but only until the processing
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* threads shutdown (which is quick)
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* If this returns 0, it is safe to call {@link ParallelProcessor#waitUntilDone()} while will block until the worker threads shutdown
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*/
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public
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float getProgress() {
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int i = currentProgress.get();
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if (this.totalWorkload == -1) {
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return (float) i;
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}
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if (i == 0) {
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return 0.0f;
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}
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