多线程——Executor、ExecutorService、Executors三者的区别

Executor、ExecutorService、Executors三者的区别：

层次关系：

public interface ExecutorService extends Executor {}
public abstract class AbstractExecutorService implements ExecutorService {}
public interface ScheduledExecutorService extends ExecutorService {}

public class ThreadPoolExecutor extends AbstractExecutorService {}
public class ScheduledThreadPoolExecutor extends ThreadPoolExecutor implements ScheduledExecutorService {}

 

区别：

　　1.ExecutorService 接口继承了Executor 接口，是Executor 的子接口。

 

　　2.Executor接口中定义了execute()方法，用来接收一个Runnable接口的对象，

　　  　　 而ExecutorService接口中定义的submit()方法可以接收Runnable和Callable接口对象。

 

　　3.Executor接口中execute()方法不返回任何结果，而ExecutorService接口中submit()方法可以通过一个 Future 对象返回运算结果。

 

　　4.Executor和ExecutorService除了允许客户端提交一个任务，ExecutorService 还提供用来控制线程池的方法。

　　   　　比如：调用 shutDown() 方法终止线程池。

 

　　5.Executors 类提供工厂方法用来创建不同类型的线程池。比如: 

 　　 　newSingleThreadExecutor() 创建一个只有一个线程的线程池，

   　　newFixedThreadPool(int numOfThreads)来创建固定线程数的线程池，

   　　newCachedThreadPool()创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。

 　　　　newScheduledThreadPool(int corePoolSize) 创建一个线程池，它可安排在给定延迟后运行命令或者定期地执行。

 

下面是部分源码：

public interface Executor {
    void execute(Runnable command);
}

public interface ExecutorService extends Executor {
    void shutdown();
    List<Runnable> shutdownNow();
    boolean isShutdown();
    boolean isTerminated();
    boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException;
    <T> Future<T> submit(Callable<T> task);
    <T> Future<T> submit(Runnable task, T result);
    Future<?> submit(Runnable task);
    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) throws InterruptedException;
    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, throws InterruptedException;
    <T> T invokeAny(Collection<? extends Callable<T>> tasks)  throws InterruptedException, ExecutionException;
    <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
                                  throws InterruptedException,ExecutionException, TimeoutException;
}

public class Executors {

    /** Cannot instantiate. */
    private Executors() {}

    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
    }
    public static ExecutorService newWorkStealingPool(int parallelism) {
        return new ForkJoinPool (parallelism,ForkJoinPool.defaultForkJoinWorkerThreadFactory,null, true);
    }

    public static ExecutorService newWorkStealingPool() {
        return new ForkJoinPool (Runtime.getRuntime().availableProcessors(), ForkJoinPool.defaultForkJoinWorkerThreadFactory,null, true);
    }

    public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS,  new LinkedBlockingQueue<Runnable>(),threadFactory);
    }

    public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1,0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
    }

    public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
        return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>(), threadFactory));
    }

    public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS,new SynchronousQueue<Runnable>());
    }

    public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(),threadFactory);
    }

    public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
        return new DelegatedScheduledExecutorService (new ScheduledThreadPoolExecutor(1));
    }

    public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
        return new DelegatedScheduledExecutorService (new ScheduledThreadPoolExecutor(1, threadFactory));
    }

    public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

    public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory) {
        return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
    }

    public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
        if (executor == null)
            throw new NullPointerException();
        return new DelegatedExecutorService(executor);
    }

    public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
        if (executor == null)
            throw new NullPointerException();
        return new DelegatedScheduledExecutorService(executor);
    }

    public static ThreadFactory defaultThreadFactory() {
        return new DefaultThreadFactory();
    }

    public static ThreadFactory privilegedThreadFactory() {
        return new PrivilegedThreadFactory();
    }

    public static <T> Callable<T> callable(Runnable task, T result) {
        if (task == null)
            throw new NullPointerException();
        return new RunnableAdapter<T>(task, result);
    }

    public static Callable<Object> callable(Runnable task) {
        if (task == null)
            throw new NullPointerException();
        return new RunnableAdapter<Object>(task, null);
    }
    public static Callable<Object> callable(final PrivilegedAction<?> action) {
        if (action == null)
            throw new NullPointerException();
        return new Callable<Object>() {
            public Object call() { return action.run(); }};
    }

    public static Callable<Object> callable(final PrivilegedExceptionAction<?> action) {
        if (action == null)
            throw new NullPointerException();
        return new Callable<Object>() {
            public Object call() throws Exception { return action.run(); }};
    }

    public static <T> Callable<T> privilegedCallable(Callable<T> callable) {
        if (callable == null)
            throw new NullPointerException();
        return new PrivilegedCallable<T>(callable);
    }
    public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> callable) {
        if (callable == null)
            throw new NullPointerException();
        return new PrivilegedCallableUsingCurrentClassLoader<T>(callable);
    }
}

/** 表示异步计算的结果。 */
public interface Future<V> {

    /**
     * 试图取消对此任务的执行
     */
    boolean cancel(boolean mayInterruptIfRunning);

    /**
     *如果在任务正常完成前将其取消，则返回 true。
     */
    boolean isCancelled();

    /**
     * 如果任务已完成，则返回 true。
     */
    boolean isDone();

    /**
     *如有必要，等待计算完成，然后获取其结果。
     */
    V get() throws InterruptedException, ExecutionException;

    /**
     *如有必要，最多等待为使计算完成所给定的时间之后，获取其结果（如果结果可用）。
     */
    V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}