读AbstractExecutorService_JAVA_编程开发_程序员俱乐部

class="java">
//他是ExecutorService的部分实现
public abstract class AbstractExecutorService implements ExecutorService

//提交一个Runnable任务给AbstractExecutorService执行返回Future
public Future<?> submit(Runnable task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<Void> ftask = newTaskFor(task, null);
        execute(ftask);
        return ftask;
    }

protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
        return new FutureTask<T>(runnable, value);
    }

//提交一个Runnable任务并指定返回值给AbstractExecutorService执行返回Future
public <T> Future<T> submit(Runnable task, T result) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task, result);
        execute(ftask);
        return ftask;
    }

//提交一个Callable任务并指定返回值给AbstractExecutorService执行返回Future
public <T> Future<T> submit(Callable<T> task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task);
        execute(ftask);
        return ftask;
    }


//一旦有任务执行成功就返回
public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
        throws InterruptedException, ExecutionException {
        try {
            return doInvokeAny(tasks, false, 0);
        } catch (TimeoutException cannotHappen) {
            assert false;
            return null;
        }
    }

private <T> T doInvokeAny(Collection<? extends Callable<T>> tasks,
                            boolean timed, long nanos)
        throws InterruptedException, ExecutionException, TimeoutException {
        if (tasks == null)
            throw new NullPointerException();
        int ntasks = tasks.size();
        if (ntasks == 0)
            throw new IllegalArgumentException();
        List<Future<T>> futures= new ArrayList<Future<T>>(ntasks);
        ExecutorCompletionService<T> ecs =
            new ExecutorCompletionService<T>(this);

        try {
            
            ExecutionException ee = null;
            long lastTime = timed ? System.nanoTime() : 0;
            Iterator<? extends Callable<T>> it = tasks.iterator();
            //将任务加入到futures集合中
            futures.add(ecs.submit(it.next()));
            --ntasks;
            int active = 1;

            for (;;) {
	       //获取Future
                Future<T> f = ecs.poll();
		//当前没有完成的任务
                if (f == null) {
		    //还有任务未提交
                    if (ntasks > 0) {
                        --ntasks;
			//再提交一个任务
                        futures.add(ecs.submit(it.next()));
                        ++active;
                    }
		    //没有活动的任务重新循环
                    else if (active == 0)
                        break;
	            //如果有超时
                    else if (timed) {
                        f = ecs.poll(nanos, TimeUnit.NANOSECONDS);
			//超时抛出异常
                        if (f == null)
                            throw new TimeoutException();
                        long now = System.nanoTime();
                        nanos -= now - lastTime;
                        lastTime = now;
                    }
                    else
		        //都没有则阻塞获取Future
                        f = ecs.take();
                }
                if (f != null) {
                    --active;
                    try {
                        return f.get();
                    } catch (ExecutionException eex) {
                        ee = eex;
                    } catch (RuntimeException rex) {
                        ee = new ExecutionException(rex);
                    }
                }
            }

            if (ee == null)
                ee = new ExecutionException();
            throw ee;

        } finally {
            for (Future<T> f : futures)
	       //尝试取消完成的任务
                f.cancel(true);
        }
    }


//一旦有任务执行成功就返回,超时抛出异常
   public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                           long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException {
        return doInvokeAny(tasks, true, unit.toNanos(timeout));
    }


//执行所有Futrue返回完成任务的Future列表
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
        throws InterruptedException {
        if (tasks == null)
            throw new NullPointerException();
        List<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
        boolean done = false;
        try {
            for (Callable<T> t : tasks) {
                RunnableFuture<T> f = newTaskFor(t);
                futures.add(f);
                execute(f);
            }
            for (Future<T> f : futures) {
	        //如果任务还没有完成
                if (!f.isDone()) {
                    try {
		       //获取
                        f.get();
                    } catch (CancellationException ignore) {
                    } catch (ExecutionException ignore) {
                    }
                }
            }
            done = true;
            return futures;
        } finally {
	     //如果没有任务完成,尝试取消Future
            if (!done)
                for (Future<T> f : futures)
                    f.cancel(true);
        }
    }


//执行所有任务返回所有未超时并且执行了的任务
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                         long timeout, TimeUnit unit)
        throws InterruptedException {
        if (tasks == null || unit == null)
            throw new NullPointerException();
        long nanos = unit.toNanos(timeout);
        List<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
        boolean done = false;
        try {
            for (Callable<T> t : tasks)
                futures.add(newTaskFor(t));

            long lastTime = System.nanoTime();

            
            Iterator<Future<T>> it = futures.iterator();
            while (it.hasNext()) {
                execute((Runnable)(it.next()));
                long now = System.nanoTime();
                nanos -= now - lastTime;
                lastTime = now;
		//超时了直接返回
                if (nanos <= 0)
                    return futures;
            }

            for (Future<T> f : futures) {
	        //如果任务还为完成
                if (!f.isDone()) {
		   //超时了直接返回
                    if (nanos <= 0)
                        return futures;
                    try {
                        f.get(nanos, TimeUnit.NANOSECONDS);
                    } catch (CancellationException ignore) {
                    } catch (ExecutionException ignore) {
                    } catch (TimeoutException toe) {
		        //超时异常直接返回
                        return futures;
                    }
                    long now = System.nanoTime();
                    nanos -= now - lastTime;
                    lastTime = now;
                }
            }
            done = true;
            return futures;
        } finally {
	    //所有任务并没有全部返回(可能抛出异常等)
            if (!done)
                for (Future<T> f : futures)
                    f.cancel(true);
        }
    }