java - 等待 0 延迟的预定 future 的最佳方式是什么？

Question

我试图避免让当前线程 hibernate ，直到 ScheduledFuture 以 0 延迟执行。不幸的是，我找不到一个针对 future 的钩子(Hook)来通知可运行对象何时执行。所讨论的 future 包装了 guava cache.put(key,value) 操作。应在缓存使 key 过期之前调用可运行对象...本质上，我希望一个 key 永不过期。

    final Runnable refresh = new Runnable() {
        @Override
        public void run()
        {
            cache.put( key, value );
        }
    };

    // replace the token when 95% of the ttl has passed
    long refreshInterval = (long)( keyExpires * 1000 *
                                   0.5 );

    // execute the future task and then delay the current thread long enough for the
    // executor to process the runnable. 50 ms should be long enough.
    ScheduledFuture<?> future = scheduler.scheduleAtFixedRate( refresh,
                                                               0,
                                                               refreshInterval,
                                                               TimeUnit.MILLISECONDS );

   /// this is the code I'd like to avoid
   try {
        Thread.sleep( 50 );
    } catch( InterruptedException e1 ) {} catch( ExecutionException e ) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

执行器服务确实会立即运行代码，但启动线程有延迟时间。该延迟将是系统特定的，因此我想避免任意 sleep 。

我正在使用 ScheduledThreadPoolExecutor 创建 ScheduledFuture，并且我可以使用该类型的访问器(例如 isDone())获得我想要的行为。然而，这似乎也很古怪。是否有一个更干净的实现，可以提供 hibernate 当前线程的行为，而不使用 Executor 服务的副作用？

谢谢，罗宾

编辑:显示没有 Thread.sleep() 时失败的测试

    cache.putNonExpiring( "key", "value" );
    Assert.assertNotNull( "Immediate get should have value", cache.get( "key" ) );

要正常工作，应同步执行 put(key,value) 以允许立即执行 get(key) 操作。

Answer 1

也许您可以使用当前线程阻塞的信​​号量或其他同步类型，直到刷新可运行对象释放信号量

// A semaphore initialized with no permits
final Semaphore runnableExecuting = new Sempahore(0);

final Runnable refresh = new Runnable()
{
    @Override
    public void run()
    {
        // Release one permit.  This should unblock the thread
        // scheduled this task.  After the initial releasing
        // the semaphore is essentially unneeded
        runnableExecuting.release();

        // Your code
    }
}

// After executor scheduling

// Attempt to acquire a permit, which the semphore initially has none.
// This will block until a permit becomes available
runnableExecuting.acquire();