Support WASM threads

[Joe-Palmer]

Multi-threading support is coming to WASM and has just finished an origin trial in Chrome! Continuing in my effort to use the VP9 encoder, I had to explicitly set the encoder to use 1 thread which got it working. However, while this allows the development of our solution to continue, it is too slow to use in a practice.

I have been trying to use the new WASM threading support by enabling this flag and increasing the g_threads by it goes back to giving the original error.

So my questions are, should it be theoretically possible to use WASM threads to support multi-threading in the VP9 encoder? Should it just be a matter of getting the compilation and implementation correct or would the actual VP9 encoder need changing? Is this something that may one day be officially supported in this project? Do you have any tips or suggestions for me to continue working on this?

Many thanks for any advice you can provide.

[surma]

Theoretically it should be possible to use threads with VP8 and VP9. I am not sure why this is turning out to be complicated.

I’ll loop in @RReverser on this in case he has some bandwidth to take a look — both #7 and this. Supporting VP9 and threading should probably all be separate builds, but I think it’d be great to offer them.

[Joe-Palmer]

That's great, thanks @surma and @RReverser!

I have successfully got lossless VP9 encoding reasonably fast (depending on CPU power). I have committed just the encoder configuration changes to this branch:

https://github.com/Joe-Palmer/webm-wasm/pull/1/files

I also made some changes to the live demo in another branch to support the new VP9 encoding:

https://github.com/Joe-Palmer/webm-wasm/blob/vp9/demo/live.html

When I tried adding -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=2 from this post to the build command, I got this error:

shared:ERROR: Memory growth is not yet supported with pthreads

So I removed -s ALLOW_MEMORY_GROWTH=1 and then I got this error:

shared:ERROR: only dlmalloc is possible when using pthreads

So I then switched emmalloc to dlmalloc and it compiled! But then when I load the demo page I get this error in the browser:

And this is as far as I got as I ran out of ideas of what to try next. Hopefully someone that understands this better then me can pick it up, it feels close.

Let me know if there is anything else I can try or do to help.

[sky0014]

Probably your xhr url has some problem，change

webm-wasm/build.sh

Line 15 in 15e06bb

export OPTIMIZE="-Os"

this to -O1 will make it better to debug.

[alectrocute]

@Joe-Palmer Did you ever figure this one out?

[Joe-Palmer]

Unfortunately not 😕

[RReverser]

I think a lot has changed since the issues described (e.g. memory growth with threads is definitely supported now), so it's just worth for someone to try again.