Future
Future接口的几个方法
- boolean cancel(boolean mayInterruptIfRunning); 取消未完成的任务,中断执行中的任务
- boolean isCancelled(); 是否完成前被取消
- boolean isDone();
- V get() throws InterruptedException, ExecutionException; 阻塞当前线程等任务完成
- V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException; 指定一个等待的超时时间
/**
* Attempts to cancel execution of this task. This attempt will
* fail if the task has already completed, has already been cancelled,
* or could not be cancelled for some other reason. If successful,
* and this task has not started when {@code cancel} is called,
* this task should never run. If the task has already started,
* then the {@code mayInterruptIfRunning} parameter determines
* whether the thread executing this task should be interrupted in
* an attempt to stop the task.
*
* <p>After this method returns, subsequent calls to {@link #isDone} will
* always return {@code true}. Subsequent calls to {@link #isCancelled}
* will always return {@code true} if this method returned {@code true}.
*
* @param mayInterruptIfRunning {@code true} if the thread executing this
* task should be interrupted; otherwise, in-progress tasks are allowed
* to complete
* @return {@code false} if the task could not be cancelled,
* typically because it has already completed normally;
* {@code true} otherwise
*/
boolean cancel(boolean mayInterruptIfRunning);
/**
* @return {@code true} if this task was cancelled before it completed
*/
boolean isCancelled();
/**
* Returns {@code true} if this task completed.
*
* Completion may be due to normal termination, an exception, or
* cancellation -- in all of these cases, this method will return
* {@code true}.
*
* @return {@code true} if this task completed
*/
boolean isDone();
/**
* Waits if necessary for the computation to complete, and then
* retrieves its result.
*
* @return the computed result
* @throws CancellationException if the computation was cancelled
* @throws ExecutionException if the computation threw an
* exception
* @throws InterruptedException if the current thread was interrupted
* while waiting
*/
V get() throws InterruptedException, ExecutionException;
/**
* Waits if necessary for at most the given time for the computation
* to complete, and then retrieves its result, if available.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @return the computed result
* @throws CancellationException if the computation was cancelled
* @throws ExecutionException if the computation threw an
* exception
* @throws InterruptedException if the current thread was interrupted
* while waiting
* @throws TimeoutException if the wait timed out
*/
V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}
FutureTask
FutureTask 实现了 Runnable 和 Future 接口,由于实现了 Runnable 接口,所以可以将 FutureTask 对象作为任务提交给ThreadPoolExecutor 去执行,也可以直接被 Thread 执行;又因为实现了 Future 接口,所以也能用来获得任务的执行结果。
茶壶烧水问题
多种办法,例如 Thread.join()、CountDownLatch,甚至阻塞队列都可以解决,不过今天我们用 Future特性来实现。
public class ThreadPoolDemo {
public static void main(String[] args) throws ExecutionException, InterruptedException {
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 4, 5, TimeUnit.SECONDS,
new LinkedBlockingQueue<>(), r -> new Thread(r, "bb-thread-" + r.hashCode()));
FutureTask<String> t1 = new FutureTask<>(new Task1());
FutureTask<String> t2 = new FutureTask<>(new Task2(t1));
threadPoolExecutor.submit(t1);
threadPoolExecutor.submit(t2);
System.out.println(t2.get());
}
}
class Task1 implements Callable<String>{
@Override
public String call() throws Exception {
System.out.println("洗茶壶...");
TimeUnit.SECONDS.sleep(1);
System.out.println("洗茶杯...");
TimeUnit.SECONDS.sleep(2);
System.out.println("拿茶叶...");
TimeUnit.SECONDS.sleep(1);
return " 龙井 ";
}
}
class Task2 implements Callable<String>{
FutureTask<String> task1futureTask;
public Task2(FutureTask<String> task1futureTask) {
this.task1futureTask = task1futureTask;
}
@Override
public String call() throws Exception {
System.out.println("洗水壶...");
TimeUnit.SECONDS.sleep(1);
System.out.println("烧开水...");
TimeUnit.SECONDS.sleep(5);
// 获取另外线程的执行结果
String tf = task1futureTask.get();
System.out.println("拿到茶叶:"+tf);
System.out.println("泡茶...");
return "上茶:" + tf;
}
}