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Re: Threaded RS232 communication

by BrowserUk (Pope)
on Jan 30, 2013 at 10:48 UTC ( #1016023=note: print w/ replies, xml ) Need Help??


in reply to Threaded RS232 communication

First off, you are probably limiting your audience unnecessarily by mentioning "threads" in the title.

Your basic problem, that of needing a non-blocking read, has nothing to do with threading.

Secondly, do you really need to terminate your read thread? That is, if you detached it, it would just silently melt into the ether when your main thread decides to exit the process.

But if you do really need to, I think that you've already discovered the 'right' solution, namely read_bg(). All you nee to do is use the API correctly and alter your coding strategy a little. (NOTE: None of the following is tested.)

So I changed to "background read" my ($receivedBytes, $data) = $HandleToRS232->read_bg(); Doing this I got nothing in $data so I did a call to my($done, $count_in, $string_in) = $HandleToRS232->read_done(1); Then I receive the message in the $string_in variable, but the call to read_done is also blocking.

Based on my reading the source -- and I may well have misread it --

  • read_bg() uses overlapped IO to operate, therefore it is expected that it will (often) not return (somplete) data immediately

    It basically says, this is what I want to read, initiate that for me and return immediately (with any data that happens to have already arrived.)

    I'll call read_done() when I'm ready for (the rest of) it.

  • read_done() is only blocking if you pass a true argument (As you are:read_done(1);).

    To prevent it from blocking, pass 0;

    That will require you to recode your read thread so that instead of blocking in a read, you poll (with a delay!).

    Then within that polling loop you can check to see if you should exit the thread.


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Re^2: Threaded RS232 communication
by tobias_hofer (Friar) on Jan 30, 2013 at 13:48 UTC

    I went back to $HandleRS232->read();
    Because it is simpler for me and simply meets the requirements.
    I have also detached the threads so they can go into the ether. :-D
    It working perfect! Super!

    Thanks a lot!

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