Java并发编程（2）--Executor

时间：2022-02-13 14:51:25

一、Executor

Java SE5的java.util.concurrent包中的执行器（Executor）将为你管理Thread对象，从而简化了并发编程。Executor在客户端和执行任务之间提供了一个间接层，Executor代替客户端执行任务。Executor允许你管理异步任务的执行，而无须显式地管理线程的生命周期。

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

二、ExcutorService

ExecutorService扩展了Executor并添加了一些生命周期管理的方法。一个Executor的生命周期有三种状态，运行 ，关闭 ，终止 。

public interface ExecutorService extends Executor {
//关闭线程池，不允许新的任务，但正在等待的任务会被执行。
void shutdown();
//关闭线程池，试图停止正在执行的任务，不允许新的任务，抛弃正在等待的任务并返回。
    List<Runnable> shutdownNow();
//线程池是否已经关闭
boolean isShutdown();
//线程池是否终止（所有线程都已经关闭）
boolean isTerminated();
//阻塞等待一段时间直到线程池被终止或超时或发生中断异常
boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException;
//提交一个任务，返回任务的future对象，可以知道任务的执行情况
    Future<T> submit(Callable<T> task);
//同上
    Future<T> submit(Runnable task, T result);
//同上
    Future<?> submit(Runnable task);
//批量执行任务，全部执行完再返回
    List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException;
//批量执行任务，全部执行完或超时了就返回
    List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException;
//批量执行任务，成功完成一个就返回
    T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException;
//批量执行任务，成功完成一个或超时就返回
    T invokeAny(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}

三、ThreadPoolExecutor

ThreadPoolExecutor是ExecutorService的一个实现类，它使用可能的几个池线程之一执行每个提交的任务，通常使用 Executors 工厂方法配置。

   public ThreadPoolExecutor(int corePoolSize,//核心线程数
int maximumPoolSize,//最大线程数
long keepAliveTime,//空闲线程存活时间
                              TimeUnit unit,//时间单位
                              BlockingQueue<Runnable> workQueue,//阻塞队列
                              ThreadFactory threadFactory,//线程工厂
                              RejectedExecutionHandler handler
                              //执行阻塞了的时候使用的Handler) {
if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}

public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
}

public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             threadFactory, defaultHandler);
}

public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              RejectedExecutionHandler handler) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), handler);
}

四、Executors

Executors类，提供了一系列工厂方法用于创建线程池，返回的线程池都实现了ExecutorService接口。

public static ExecutorService newFixedThreadPool(int nThreads)
创建固定数目线程的线程池。

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

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

public static ExecutorService newCachedThreadPool()
创建一个可缓存的线程池，调用execute 将重用以前构造的线程（如果线程可用）。如果现有线程没有可用的，则创建一个新线程并添加到池中。终止并从缓存中移除那些已有 60 秒钟未被使用的线程。

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 ExecutorService newSingleThreadExecutor()
创建一个单线程化的Executor。

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 ScheduledExecutorService newScheduledThreadPool(int corePoolSize)
创建一个支持定时及周期性的任务执行的线程池，多数情况下可用来替代Timer类。

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

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