Read timeout becomes immediate after a number of timed out read attempts

[craigraw]

I am finding that a configured read timeout is not respected when communicating with an ESP32 device. The code is fairly straightforward:

serialPort.openPort();
serialPort.setComPortParameters(115200, 8, 1, 0);
serialPort.setComPortTimeouts(SerialPort.TIMEOUT_READ_SEMI_BLOCKING, 500, 1000);
serialPort.clearRTS();
serialPort.clearDTR();

//write to port, then wait for response as follows:

InputStream in = serialPort.getInputStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] readBuffer = new byte[64];
int numBytes;

while(true) {
    long time = System.currentTimeMillis();
    try {
        while((numBytes = in.read(readBuffer)) != -1) {
            if(numBytes > 0) {
                baos.write(readBuffer, 0, numBytes);
            }
        }
    } catch(SerialPortTimeoutException e) {
        System.out.println("Timed out after " + (System.currentTimeMillis() - time) + " ms");
    }
}

This results in the following output:

Timed out after 578 ms true
Timed out after 609 ms true
Timed out after 502 ms true
Timed out after 502 ms true
Timed out after 501 ms true
Timed out after 502 ms true
Timed out after 501 ms true
Timed out after 501 ms true
Timed out after 277 ms
Timed out after 0 ms
Timed out after 0 ms
Timed out after 0 ms
Timed out after 0 ms
Timed out after 0 ms
<repeated endlessly until the ESP32 sends data>

[craigraw]

Update: This issue appears to be caused by the nature of the USB connection. I was able to avoid it by connecting directly rather than through a USB hub, although it's still a mystery why this would cause immediate read timeouts.