讀AbstractExecutorService

//他是ExecutorService的部分實現
public abstract class AbstractExecutorService implements ExecutorService

//提交一個Runnable任務給AbstractExecutorService執行返回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);
    }

//提交一個Runnable任務並指定返回值給AbstractExecutorService執行返回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;
    }

//提交一個Callable任務並指定返回值給AbstractExecutorService執行返回Future
public <T> Future<T> submit(Callable<T> task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task);
        execute(ftask);
        return ftask;
    }


//一旦有任務執行成功就返回
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();
            //將任務加入到futures集合中
            futures.add(ecs.submit(it.next()));
            --ntasks;
            int active = 1;

            for (;;) {
	       //獲取Future
                Future<T> f = ecs.poll();
		//當前沒有完成的任務
                if (f == null) {
		    //還有任務未提交
                    if (ntasks > 0) {
                        --ntasks;
			//再提交一個任務
                        futures.add(ecs.submit(it.next()));
                        ++active;
                    }
		    //沒有活動的任務重新循環
                    else if (active == 0)
                        break;
	            //如果有超時
                    else if (timed) {
                        f = ecs.poll(nanos, TimeUnit.NANOSECONDS);
			//超時拋出異常
                        if (f == null)
                            throw new TimeoutException();
                        long now = System.nanoTime();
                        nanos -= now - lastTime;
                        lastTime = now;
                    }
                    else
		        //都沒有則阻塞獲取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)
	       //嘗試取消完成的任務
                f.cancel(true);
        }
    }


//一旦有任務執行成功就返回,超時拋出異常
   public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                           long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException {
        return doInvokeAny(tasks, true, unit.toNanos(timeout));
    }


//執行所有Futrue返回完成任務的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) {
	        //如果任務還沒有完成
                if (!f.isDone()) {
                    try {
		       //獲取
                        f.get();
                    } catch (CancellationException ignore) {
                    } catch (ExecutionException ignore) {
                    }
                }
            }
            done = true;
            return futures;
        } finally {
	     //如果沒有任務完成,嘗試取消Future
            if (!done)
                for (Future<T> f : futures)
                    f.cancel(true);
        }
    }


//執行所有任務返回所有未超時並且執行了的任務
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;
		//超時了直接返回
                if (nanos <= 0)
                    return futures;
            }

            for (Future<T> f : futures) {
	        //如果任務還爲完成
                if (!f.isDone()) {
		   //超時了直接返回
                    if (nanos <= 0)
                        return futures;
                    try {
                        f.get(nanos, TimeUnit.NANOSECONDS);
                    } catch (CancellationException ignore) {
                    } catch (ExecutionException ignore) {
                    } catch (TimeoutException toe) {
		        //超時異常直接返回
                        return futures;
                    }
                    long now = System.nanoTime();
                    nanos -= now - lastTime;
                    lastTime = now;
                }
            }
            done = true;
            return futures;
        } finally {
	    //所有任務並沒有全部返回(可能拋出異常等)
            if (!done)
                for (Future<T> f : futures)
                    f.cancel(true);
        }
    }