Question

让我们在应用程序中有一个经典的Executor。应用程序的许多部分使用此执行程序进行某些计算，每个计算都可以取消，为此我可以在Executor上调用shutdown()或shutdownNow()。

但我想只关闭Executor中的部分任务。遗憾的是，我无法访问Future个对象，它们是计算实现的私有部分（实际上计算由actor框架jetlang支持）

我想要像Executor包装器这样的东西，我可以传递给计算，并且应该由真正的Executor支持。像这样：

// main application executor
Executor applicationExecutor = Executors.newCachedThreadPool();

// starting computation
Executor computationExecutor = new ExecutorWrapper(applicationExecutor);
Computation computation = new Computation(computationExecutor);
computation.start();

// cancelling computation
computation.cancel();
// shutting down only computation tasks
computationExecutor.shutdown();

// applicationExecutor remains running and happy

还是其他任何想法？

Answer 1

对于那些希望获得好结果的人：有最终解决方案，部分基于Ivan Sopov的回答。幸运的是，jetlang只用Executor接口（而不是ExecutorService）来运行它的任务，所以我创建了一个包装类，它支持只停止由这个包装器创建的任务。

static class StoppableExecutor implements Executor {
    final ExecutorService executor;
    final List<Future<?>> futures = Lists.newArrayList();
    boolean stopped;

    public StoppableExecutor(ExecutorService executor) {
        this.executor = executor;
    }

    void stop() {
        this.stopped = true;
        synchronized (futures) {
            for (Iterator<Future<?>> iterator = futures.iterator(); iterator.hasNext();) {
                Future<?> future = iterator.next();
                if (!future.isDone() && !future.isCancelled()) {
                    System.out.println(future.cancel(true));
                }
            }
            futures.clear();
        }
    }

    @Override
    public void execute(Runnable command) {
        if (!stopped) {
            synchronized (futures) {
                Future<?> newFuture = executor.submit(command);
                for (Iterator<Future<?>> iterator = futures.iterator(); iterator.hasNext();) {
                    Future<?> future = iterator.next();
                    if (future.isDone() || future.isCancelled())
                        iterator.remove();
                }
                futures.add(newFuture);
            }
        }
    }
}

使用它非常简单：

ExecutorService service = Executors.newFixedThreadPool(5);
StoppableExecutor executor = new StoppableExecutor(service);

// doing some actor stuff with executor instance
PoolFiberFactory factory = new PoolFiberFactory(executor);

// stopping tasks only created on executor instance
// executor service is happily running other tasks
executor.stop();

这就是全部。效果很好。

Answer 2

在设置布尔标志之前，如何让Computation成为Runnable（并使用提供的Executor运行）？有点像：

public class Computation
{
  boolean volatile stopped;

  public void run(){
    while(!stopped){
    //do magic
  }

  public void cancel)(){stopped=true;}
}

你正在做的事实上是停止线程。但是，它不会被垃圾收集，而是重新使用，因为它由Executor管理。查看“停止线程的正确方法是什么？”。

编辑：请注意上面的代码是非常原始的，因为它假设while循环的主体需要很短的时间。如果没有，检查将很少执行，您会发现取消任务与实际停止之间有延迟。

Answer 3

这样的东西？您可以部分关闭：

for (Future<?> future : %ExecutorServiceWrapperInstance%.getFutures()) {
    if (%CONDITION%) {
        future.cancel(true);
    }
}

以下是代码：

package com.sopovs.moradanen;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

public class ExecutorServiceWrapper implements ExecutorService {

private final ExecutorService realService;
private List<Future<?>> futures = new ArrayList<Future<?>>();

public ExecutorServiceWrapper(ExecutorService realService) {
    this.realService = realService;
}

@Override
public void execute(Runnable command) {
    realService.execute(command);
}

@Override
public void shutdown() {
    realService.shutdown();

}

@Override
public List<Runnable> shutdownNow() {
    return realService.shutdownNow();
}

@Override
public boolean isShutdown() {
    return realService.isShutdown();
}

@Override
public boolean isTerminated() {
    return realService.isTerminated();
}

@Override
public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
    return realService.awaitTermination(timeout, unit);
}

@Override
public <T> Future<T> submit(Callable<T> task) {
    Future<T> future = realService.submit(task);
    synchronized (this) {
        futures.add(future);
    }
    return future;
}

public synchronized List<Future<?>> getFutures() {
    return Collections.unmodifiableList(futures);
}

@Override
public <T> Future<T> submit(Runnable task, T result) {
    Future<T> future = realService.submit(task, result);
    synchronized (this) {
        futures.add(future);
    }
    return future;
}

@Override
public Future<?> submit(Runnable task) {
    Future<?> future = realService.submit(task);
    synchronized (this) {
        futures.add(future);
    }
    return future;
}

@Override
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) throws InterruptedException {
    List<Future<T>> future = realService.invokeAll(tasks);
    synchronized (this) {
        futures.addAll(future);
    }
    return future;
}

@Override
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
        throws InterruptedException {
    List<Future<T>> future = realService.invokeAll(tasks, timeout, unit);
    synchronized (this) {
        futures.addAll(future);
    }
    return future;
}

@Override
public <T> T invokeAny(Collection<? extends Callable<T>> tasks) throws InterruptedException, ExecutionException {
    //don't know what to do here. Maybe this method is not needed by the framework
    //than just throw new NotImplementedException();
    return realService.invokeAny(tasks);
}

@Override
public <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException {
    //don't know what to do here. Maybe this method is not needed by the framework
    //than just throw new NotImplementedException();
    return realService.invokeAny(tasks, timeout, unit);
}
}

Java Executor部分关闭

3 个答案: