Cancel Reading Over A Socket

I am attempting to cancel a running process that is reading data
coming in via a socket from an external (non-Java) application. The
cancel *does* work, except I always get an exception. Here is the
code in question...

    private void process() throws ProcessException {
        socketWriter.println("START PROCESSING");

        try {
            File outFile = new File(workingFolder, "output.txt");
            FileWriter fw = new FileWriter(outFile, false);
            BufferedWriter bw = new BufferedWriter(fw);

            String line = socketReader.readLine();
            while
(line.indexOf(NativeProcessDistributed.COMPLETED_RUN) == -1) {
                bw.write(line);
                bw.newLine();
                line = socketReader.readLine();
            }

            bw.flush();
        } catch (IOException e) {
            throw new
ProcessException(NativeProcess.CANT_WRITE_OUTPUT);
        }
    }

Basically, I start the processing (via START PROCESSING written to the
application) and then watch the input for a string that means the run
has completed. Until then, I write out all output to an output file
(so someone can examine the output if anything goes wrong with the
processing).

I want the user to cancel the run at any time in the GUI via a cancel
button. This is the method that's fired when the cancel button is
pressed

    public void cancel() {
        try {
            // write a suicide file/flag to force the processing to
halt
            File suicide = new File(runFolder + SUICIDE_FILE);
            suicide.createNewFile();

            this.cleanup();

            status = CANCELLED;
            stateChanged();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

The cleanup() method is as follows:

    private void cleanup() {
        try {
            socketReader.close();
            socketWriter.close();
            clientSocket.close();
            nativeProcess.destroy();
        } catch (IOException e) {
        }
    }

What's happening (as far as I can tell) is that I'm closing the
clientSocket while the "while" loop in the process() method is still
looping, thus causing the exception to be thrown. I am not sure how
to sync the two methods up so that I can cancel the process AND the
while loop in the distribute method stops (the socketReader.readLine()
is what is throwing the actual exception, BTW). It may be a threading
issue, but I'm having difficulty figuring out what the issue actually
is.

Thanks for any help with this frustrating problem.