How to terminate a thread blocking on socket IO operation instantly?

Solution 1:

There are (potentially) three ways to do this:

• Calling Socket.close() on the socket will close the associated InputStream and OutputStream objects, and cause any threads blocked in Socket or (associated) stream operations to be unblocked. According to the javadoc, operations on the socket itself will throw a SocketException.

• Calling Thread.interrupt() will (under some circumstances that are not specified) interrupt a blocking I/O operation, causing it to throw an InterruptedIOException.

  ^{Note the caveat. Apparently the "interrupt()" approach doesn't work on "most" modern Java platforms. (If someone else had the time and inclination, they could possible investigate the circumstances in which this approach works. However, the mere fact that the behavior is platform specific should be sufficient to say that you should only use it if you only need your application to work on a specific platform. At which point you can easily "try it" for yourself.)}

• A possible third way to do this is to call Socket.shutdownInput() and/or Socket.shutdownOutput(). The javadocs don't say explicitly what happens with read and/or write operations that are currently blocked, but it is not unreasonable to think that they will unblock and throw an exception. However, if the javadoc doesn't say what happens then the behavior should be assumed to be platform specific.

Solution 2:

I know this question is old but as nobody seems to have solved the "mystery" of Thread.interrupt() on "modern platforms" I did some research.

This is tested on Java 8 on Windows7 (64-bit) (but it will possibly be true for other platforms as well).

Calling Thread.interrupt() does not throw an InterruptedIOException What happens is that the InputStream.read() method returns with -1 and Thread.interrupted()-flag is set.

So the following could be considered a 'corrected' read() throwing InterruptedIOException:

static final int read(Socket socket, byte[] inData) 
    throws SocketTimeoutException, // if setSoTimeout() was set and read timed out
           InterruptedIOException, // if thread interrupted
           IOException             // other erors
{
    InputStream in = socket.getInputStream();

    int readBytes = in.read( inData, 0, inData.length);

    if  ( Thread.interrupted() )
    {
        throw new InterruptedIOException( "Thread interrupted during socket read");
    }

    return readBytes;
}