How to let a mutex timeout?

Question

I want to let my modem-AT-command-writing-thread only write to the modem's /dev/ttyUSB3 when the modem-AT-command-reading-thread has seen an "OK" or an "ERROR".

This initially sounds like a job for a Mutex<()>, but I have an additional requirement: If the modem-AT-command-reading-thread does not see an "OK" or "ERROR" within three seconds, the writing thread should just get on with sending the next AT command. i.e. If the reading thread gets nothing, the writing thread should still send one of its AT commands every three seconds. (Modems' AT command interfaces are often not nicely behaved.)

At the moment, I have a workaround using mpsc::channel:

Set-up:

let (sender, receiver) = channel::<()>();

modem-AT-command-reading-thread:

if line.starts_with("OK") || line.contains("ERROR") {
    debug!("Sending go-ahead to writing_thread.");
    sender.send(()).unwrap();
}

modem-AT-command-writing-thread:

/* This receive is just a way of blocking until the modem is ready. */
match receiver.recv_timeout(Duration::from_secs(3)) {
    Ok(_) => {
        debug!("Received go-ahead from reading thread.");
        /*
         * Empty the channel, in case the modem was too effusive.  We don't want
         * to "bank" earlier OK/ERRORs to allow multiple AT commands to be sent in
         * quick succession.
         */
        while let Ok(_) = receiver.try_recv() {}
    }
    Err(err) => match err {
        RecvTimeoutError::Timeout => {
            debug!("Timed-out waiting for go-ahead from reading thread.");
        }
        RecvTimeoutError::Disconnected => break 'outer
    },
}

I cannot find a Mutex::lock_with_timeout().

How can I implement this properly, using a Mutex<()> or similar?

Answer 1

You can use parking_lot's Mutex, it has try_lock_for().