Re: sending data to an asynchronous process

[Nicolas Graner]

Jean Louis <bugs@gnu.support> wrote on 2021-04-02 20:18:
> * Nicolas Graner <nicolas@graner.name> [2021-04-02 13:21]:
>> I am writing a program that creates audio samples in an emacs
>> buffer, then sends them to an external program (sox) to play in
>> the background while I continue working with emacs. Part of the
>> code is roughly as follows:
>> 
> (setq process
>       (let ((process-connection-type nil))
>       (start-process "my-process" nil
>                      "sox" "-r" rate "-c" channels "-b" bits "-e" encoding 
> "-q" "-d")))
> (process-send-region process start end)
> (process-send-eof process)
>
> For process-send-region, it says:
>
> If PROCESS is a non-blocking network process that hasn’t been fully
> set up yet, this function will block until socket setup has completed.
>
> Maybe that applies.

No. No network involved whatsoever. Just running /usr/bin/sox which is a
regular file.

> It would be nice to show all the function you use there.

No other function is needed. If you want to reproduce the problem, just
fill a buffer with 1 MB of random binary data and evaluate this slightly
modified version of the above code:

(setq process
      (let ((process-connection-type nil))
        (start-process "my-process" nil
                       "/usr/bin/sox" "-r" "44100" "-c" "2" "-b" "32"
      "-e" "signed-integer" "-t" "raw" "-" "-q" "-d")))

(process-send-region process (point-min) (point-max))

(process-send-eof process)

If you have sox installed, be prepared to hear some horrible random noise :)
You will notice that the first expression above returns immediately as
expected, but the second (process-send-region ...) does not. That's the
problem I'm trying to solve.

> I would like to know if you play files or you feed data to sox to
> play files, where does that come from? Is it maybe an elevator
> music from an UDP port?

The data originally came from files that I read into a buffer and did
some processing on. At the time of calling the above code, all the data
is sitting quietly in an emacs buffer. No network, disk access or
anything else involved. Just sending the contents of a buffer through a
pipe to a program that was started as an asynchronous process.

Nicolas