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0 pointsjchw4y ago0 comments

I think you may be reading too much into what I said; I was working on a DAW-like toy, not a full DAW that uses VST plugins, and because I chose to write DSP code, I had to understand it. I don’t know what a real DAW looks like because I am not a subject expert.

That said, Rust seemed pretty promising for writing the audio engine of a DAW due to the memory ownership model. It was relatively easy to come up with a way to architect a very basic lock-free audio thread and feel sure that it was at least memory correct. I have no idea how a real DAW avoids certain pitfalls in the audio thread; lock-free isn’t too hard, but avoiding allocations in all circumstances seems tricky.

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PaulDavisThe1st4y ago· 1 in thread

Most DAWs do not avoid locks in RT context.

Take a listen to my interview with Justin Frankel of Reaper - somehow in our 3hr+ epic chat, he acknowledges that they don't avoid locks entirely. And Ardour, despite trying, also fails to do so. Anecdotally, from my conversations with other DAW developers, they also do no manage it 100%. As Justin put it, it's more about contention avoidance than lock avoidance.

Avoiding actual stack-based allocation is pretty easy in C++. You just have to want to do it, and remember to do it.

Memory correctness is really easy in the RT threads of a DAW precisely because they do (should) not allocate. You're dealing with pre-allocated memory blocks that do not change over time. It's almost the simplest case of memory mgmt that I know of within a DAW. I have seen several new-to-DAW developers adopting ill-advised schemes for memory mgmt in an RT context. The "list of blocks" is one pattern that I consider something to avoid (and unnecessady). Single-reader/single-writer lock-free (circular) FIFOs get you almost all the way there, for everything.

jchwOP4y ago

Interesting. I actually thought this was the case, but when I made a similar argument in a chatroom I got pretty severely roasted by people who were sure real audio engines never used locks in the audio thread. It seems like whichever way I go I’m wrong with audio :P but that’s OK, because I really am not pretending to be knowledgable here, for me it was only ever for fun.

The main reason I felt Rust was nice was simply the re-assurance that I could not, even if I wanted to, accidentally cause a data race within the confines of safe Rust. It’s not that the actual code was hard, but it did force me to ensure that what I was doing with the data model was actually safe. It wound up guiding how data flow worked in the playback engine.

Anyway, thanks for the pointer to the interview. I don’t expect myself to be writing the next Reaper or Ardour so it is probably OK if I don’t quite grok what you’re getting at. But, I do find this stuff rather interesting, so I would love to have a listen when I get a chance.

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