Linux support ?

[chris-zen]

Hi, I am wondering if could it be possible to include support for Linux (if it actually makes sense). I am not an expert in the field but would like to contribute if you give me a clue on where to start looking at.

Best

[padenot]

This is not supported at the moment because doing the classis system calls to switch to SCHED_RR require elevated privileges on Linux, and I've been writing this for Firefox, which is not running with elevated privileges.

Ideally we'd use rtkit, but it does not work on my machine (stock ubuntu 18.10), I'm missing some some caps probably. Even the program rtkit-test provided in rtkit does not work immediately. Maybe we should start by figuring out what is needed to have rtkit bump a thread to real-time prio.

[chris-zen]

@padenot thanks for the answer. After reading the rtkit announcement thread and this article, I realised how complex the topic is for Linux. Now I understand that it is not just a matter of using a lib like thread_priority to request a thread to be RT, but there are all kind of security measures that makes that a non trivial thing for the regular user (I am wondering why isn't this a problem for macOS or Win, perhaps they implement better scheduling policies for RT).

After some search for RealtimeKit, I was not able to find much information or documentation, so it is not really clear to me whether it is something dead or not, although it seems to be included in the repositories of several important distros.

I'll keep an eye for this in the background, and revisit this issue if I find new information.
Meanwhile, I'll keep using this lib for Win and macOS. Thank you very much for the contribution ;-)

[padenot]

I found a way to do this that works on my Ubuntu 18.10, without modification, and without root, as long as rtkit is installed, and it's a dep of PulseAudio, so it should be a reasonably common setup.

I'm going to update this crate when I have a minute, as it's going to be very important for us as well. I'll write something up.

Thanks for opening this issue that prompted me to have another look at this, and thanks to @jcristau here in the office that found why the rtkit examples weren't working (a nanosecond vs. microsecond unit mismatch) and fixed them. This was in fact already patched in debian, as he pointed out later.

[padenot]

#2 does most of what's needed here, thanks @jcristau.

I'll update later to something that makes sense based on the buffer size and the sample-rate, so that we request what the audio callback needs, not more, but this will work for now. I'll also check that the scheduler is truly back to normal when demoting the thread.

[chris-zen]

@padenot great news ! Thanks a lot !
Looking forward for the release to crates.io ;-)

[padenot]

Looking forward for the release to crates.io ;-)

It's been released for some time now, fwiw.