How to interrupt BufferedReader's readLine

Question

I am trying to read input from a socket line by line in multiple threads. How can I interrupt readLine() so that I can gracefully stop the thread that it\'s bl

Answer 1

you can design a Timer class around the read() block.

you need to set a timeout for your timer.

on timeout just interrupt your thread.

Answer 2

Without closing the socket, no question the best solution with the least overhead is to simply avoid using the blocking read methods until the BufferedReader is ready, or a timeout is reached.

public String readLineTimeout(BufferedReader reader, long timeout) throws TimeoutException, IOException {
    long start = System.currentTimeMillis();

    while (!reader.ready()) {
        if (System.currentTimeMillis() - start >= timeout)
            throw new TimeoutException();

        // optional delay between polling
        try { Thread.sleep(50); } catch (Exception ignore) {}
    }

    return reader.readLine(); // won't block since reader is ready
}

Answer 3

Without closing the socket:

The difficult problem isn't the BufferedReader.readLine, but the underlying read. If a thread is blocked reading, the only way to get it going is to supply some actual data or close the socket (interrupting the thread probably should work, but in practice does not).

So the obvious solution is to have two threads. One that reads the raw data, and will remain blocked. The second, will be the thread calling readLine. Pipe data from the first the second. You then have access to a lock than can be used to wakeup the second thread, and have it take appropriate action.

There are variations. You could have the first thread using NIO, with a single thread instance shared between all consumers.

Alternatively you could write a readLine that works with NIO. This could even take a a relatively simple single-threaded form, as Selector.wakeup exists and works.