是否有使用当前线程的ExecutorService？

我所追求的是一种兼容的方式来configuration使用线程池或不使用。 理想情况下，其他代码不应该受到影响。 我可以使用1个线程的线程池，但这不是我想要的。 有任何想法吗？

ExecutorService es = threads == 0 ? new CurrentThreadExecutor() : Executors.newThreadPoolExecutor(threads); // es.execute / es.submit / new ExecutorCompletionService(es) etc 

Answer 1

这是一个非常简单的Executor （不是ExecutorService ，介意你）的实现，只使用当前线程。 从“Java并发实践”中窃取这个（必读）。

 public class CurrentThreadExecutor implements Executor { public void execute(Runnable r) { r.run(); } } 

ExecutorService是一个更复杂的接口，但可以用相同的方法处理。

Answer 2

如果您不需要ExecutorService ，则可以使用Guava的MoreExecutors.newDirectExecutorService()或MoreExecutors.directExecutor() 。

如果包括番石榴太重，你可以实现一些东西几乎一样好：

 public final class SameThreadExecutorService extends ThreadPoolExecutor { private final CountDownLatch signal = new CountDownLatch(1); private SameThreadExecutorService() { super(1, 1, 0, TimeUnit.DAYS, new SynchronousQueue<Runnable>(), new ThreadPoolExecutor.CallerRunsPolicy()); } @Override public void shutdown() { super.shutdown(); signal.countDown(); } public static ExecutorService getInstance() { return SingletonHolder.instance; } private static class SingletonHolder { static ExecutorService instance = createInstance(); } private static ExecutorService createInstance() { final SameThreadExecutorService instance = new SameThreadExecutorService(); // The executor has one worker thread. Give it a Runnable that waits // until the executor service is shut down. instance.submit(new Runnable() { @Override public void run() { try { instance.signal.await(); } catch (InterruptedException e) { Thread.currentThread().interrupt(); } }}); return Executors.unconfigurableScheduledExecutorService(instance); } } 

Answer 3

Java 8风格：

Executor e = Runnable::run;

Answer 4

我写了一个基于AbstractExecutorService的ExecutorService。

 /** * Executes all submitted tasks directly in the same thread as the caller. */ public class SameThreadExecutorService extends AbstractExecutorService { //volatile because can be viewed by other threads private volatile boolean terminated; @Override public void shutdown() { terminated = true; } @Override public boolean isShutdown() { return terminated; } @Override public boolean isTerminated() { return terminated; } @Override public boolean awaitTermination(long theTimeout, TimeUnit theUnit) throws InterruptedException { shutdown(); // TODO ok to call shutdown? what if the client never called shutdown??? return terminated; } @Override public List<Runnable> shutdownNow() { return Collections.emptyList(); } @Override public void execute(Runnable theCommand) { theCommand.run(); } } 

Answer 5

您可以使用RejectedExecutionHandler在当前线程中运行任务。

 public static final ThreadPoolExecutor CURRENT_THREAD_EXECUTOR = new ThreadPoolExecutor(0, 0, 0, TimeUnit.DAYS, new SynchronousQueue<Runnable>(), new RejectedExecutionHandler() { public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) { r.run(); } }); 

你只需要其中的一个。

Answer 6

为了testing目的，我必须使用相同的“CurrentThreadExecutorService”，尽pipe所有build议的解决scheme都很好（特别是提到了番石榴的方法 ），但我想出了一些类似于Peter Lawrey 在此提出的内容。

正如Axelle Ziegler 在这里提到的，不幸的是，Peter的解决scheme实际上并不能正常工作，因为ThreadPoolExecutor在maximumPoolSize构造函数参数（即maximumPoolSize不能<=0 ）中引入了检查。

为了规避这一点，我做了以下几点：

 private static ExecutorService currentThreadExecutorService() { CallerRunsPolicy callerRunsPolicy = new ThreadPoolExecutor.CallerRunsPolicy(); return new ThreadPoolExecutor(0, 1, 0L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), callerRunsPolicy) { @Override public void execute(Runnable command) { callerRunsPolicy.rejectedExecution(command, this); } }; }