How to handle timeout on read with Java comm API

Question

Hi All, my app uses the Java serial comm api. From reading the docs the inputstream.read() method blocks if there is no data available.

I tried setting a timeout on the serialport object but the isReceiveTimeoutEnabled() methods returns false, indicating my driver does not natively support timeouts.

So what's the best way to implement a read timeout given the above?

Thanks, Fred

Answer 1

If its not working for you just toss that inputstream into a thread and implement your own time out. If it times out call close() on the stream to unblock and close that thread

Answer 2

You will need two threads.

A watchdog thread will monitor a reading thread and interrupt it when a timeout is detected.

Have the reading thread tell the watchdog thread that it's about to start reading, and when it completed a read.

Have the watchdog thread start a timer when a read begins and interrupt the reading thread when it times out or stop listening for a time out when the reading is complete.

Read up on Java threading if you're not familiar with it. It's easy to have multi-threading bugs.

Answer 3

You can check with the InputStream.available() method if the next read() will block or not.

Answer 4

You can also use a SerialPortEventListener as a callback to get notified of newly available data and only call read when there is something to do.

final SerialPort serialPort = ...;
final InputStream in = serialPort.getInputStream();
serialPortal.notifyOnDataAvailable(true);
serialPort.addEventListener(new SerialPortEventListener() {
    public void serialEvent(SerialPortEvent event) {
        if (event.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
            // read from InputSteam
        }
    }
});