linuxaudio.org

Paul Davis wrote:

quoted text
> On Tue, 2008-10-14 at 23:00 +0200, Olivier Guilyardi wrote:

>> This isn't the same as Jack's ring buffer. It's a little wrapper around

>> Portaudio's ring buffer, which as said above, features memory barriers. Jack's

>> ring buffer has no memory barrier AFAIK.

>

> it doesn't, but it would be nice if someone would add them. i don't know

> why people feel the need to be snarky about the "oh-so-famed JACK

> ringbuffer" ... its famed only because when we first implemented it

> nobody in the LAD community could find an open source implementation of

> the idea. i don't believe anybody has ever claimed that its the bees

> knees of lock-free ringbuffers (and if they did, they don't know what

> they are talking about). lennart also claims that the JACK

> implementation is borked because of "misuse of volatile". it would be

> nice if that was fixed too. 

I'm no memory barrier expert, but from what I read this looks like a complex

topic. Adding them to jack's ring buffer may be hazardous without carefully

crafted test cases. Bugs related to missing barriers may or may not happen

according to various hardware-related issues.
Here's what Ross Bencina says about it: "the correct implementation of these

algorithms also requires an understanding of the use of memory barriers to force

the order of some memory reads and writes on SMP systems. This is because memory

controllers may reorder reads and writes as observed by other processors on an

SMP system (or by prehipherals on a uniprocessor system)."
As a user of these projects I sense that people from Portaudio, PulseAudio and

Jack could collaborate on this topic. And Ross Bencina's initiative may be the

right place for this:

http://www.audiomulch.com/~rossb/code/lockfree/liblfds/index.htm
Best regards,
--

  Olivier Guilyardi / Samalyse

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