关闭后Java线程暂停

Question

I've managed to configure a synchronised startup for my application, and I'm not implementing the shutdown.

I'm using a CountDownLatch to await the closure of all of my threads. Each thread loops until a ( volatile ) boolean, running , flag is set to false.

Here's an example ( Caught ) Runnable being ran on a thread

System.out.println("STARTING");
startupLatch.countDown();
final BufferedReader reader = getReader();
String line;
System.out.println("STARTED");
while (running) {
    System.out.println("WAITING FOR CLOSE");
    while ((line = reader.readLine()) != null) {
        System.out.println("WAITING FOR NO MORE LINES");
        System.out.println(line);
    }
}
shutdownLatch.countDown();
System.out.println("EXITED READING THREAD: EXITS LEFT: " + shutdownLatch.getCount());

Initially I thought that the change to the running flag may not have been propogated to the thread, but it turns out that the thread is actually being blocked somewhere after reader.readLine() - thus the next iteration of the while loop can't be reached, where the shutdownLatch would be decremented.

My console output is:

STARTING

STARTED

WAITING FOR CLOSE

SHUTTING DOWN

SHUTTING DOWN come's from my close (shutdown) method.

This loop was a while(true) loop before I decided to implement the orderly shutdown; so, a blocking readline call would be fine - actually preferable to spinning off while loop iterations - because this is on another thread. However, it seem's now I need to spin off while loops in order to figure out when the shut down occurs.

• Is readline the issue here? if so:
  • Is readline supposed to be blocking?
  • How can I get around a blocking ?

Answer 1

使用reader.ready()检查下一次调用readLine()是否会阻塞当前线程

Answer 2

You can have non bocking IO only on sockets. To interrupt disk operation or any other IO of a Reader the Reader thread should be interrupted. In the most cases you will get InterruptedIOException , which will break the loop.