SDL2 application will break when using pthreads

[aliasdevelopment]

I have made a SDL2 application using the linker flag "-s USE_SDL=2" which works as expected.
I have made a ASIO application using https://github.com/emscripten-ports/asio which works as expected.
I have made a ASIO/pthread application with works as expected using the linker flags "-s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=4 -s PROXY_TO_PTHREAD=1"

But I can not merge these applications together. It seems as if USE_SDL and USE_PTHREADS/PROXY_TO_PTHREAD works against each other. I known that many older tutorials states that multithreading is not possible, but also knows that a lot of activities has been done to change this.

I get the following error when combining SDL and pthreads:
pthread-main.js onmessage() captured an uncaught exception: ReferenceError: screen is not defined

I can understand that I would make sense that the resources for rendering would only be available for the main thread, but pthread is missing some features/resources for SDL to possible.

Is it by design that USE_SDL and USE_PTHREADS/PROXY_TO_PTHREAD work against each other?
Would it be possible to use SDL from the main thread and still use pthreads for additional work?

[jakogut]

I'm encountering this same issue. USE_SDL and USE_PTHREAD/PROXY_TO_PTHREAD seem to be incompatible.

[jakogut]

Digging into the issue further, the stack trace shows:

ReferenceError: screen is not defined
    at Array.ASM_CONSTS (http://localhost:6931/test.js:1501:32)
    at _emscripten_asm_const_i (http://localhost:6931/test.js:1526:26)
    at _Emscripten_VideoInit (wasm-function[17363]:43)
    at _SDL_VideoInit (wasm-function[17486]:635)
    at _SDL_InitSubSystem (wasm-function[17481]:203)
    at _SDL_Init (wasm-function[17612]:3)
    at _main (wasm-function[310]:133)
    at Module._main (http://localhost:6931/test.js:11418:75)
    at ___call_main (http://localhost:6931/test.js:1877:24)
    at ___emscripten_thread_main (wasm-function[18150]:23)
onmessage @ test.worker.js:181

Looking at the Emscripten port of SDL2, video/emscripten/SDL_emscriptenvideo.c:145:

mode.w = EM_ASM_INT_V({
    return screen.width;
}); 

mode.h = EM_ASM_INT_V({
    return screen.height;
}); 

So it seems that the Emscripten_VideoInit function tries to get the screen dimensions from the JS object screen, but the object isn't being proxied to the new thread main is running in.

[jakogut]

I've resolved the issues with proxying EM_ASM calls in the sdl2 port (my fixes are available at https://github.com/jakogut/SDL2/tree/sdl2-proxy-pthread-fixes), now I'm getting:

TypeError: Cannot read property 'getContext' of undefined
    at Object.createContext (http://localhost:6931/test.js:6608:19)
    at _eglCreateContext (http://localhost:6931/test.js:6793:24)
    at _SDL_EGL_CreateContext (wasm-function[17463]:337)
    at _Emscripten_GLES_CreateContext (wasm-function[17453]:12)
    at _SDL_GL_CreateContext (wasm-function[17025]:143)
    at _GLES2_CreateRenderer (wasm-function[17017]:489)
    at _SDL_CreateRenderer (wasm-function[17662]:303)
    at _main (wasm-function[388]:376)
    at Module._main (http://localhost:6931/test.js:12316:33)
    at ___call_main (http://localhost:6931/test.js:2000:24)

Doing a little digging around seems to indicate that the EGL code at src/library_egl.js is unable to access the canvas object, probably because those calls need proxied as well. @kripken, can you shed any light on this issue?

[kripken]

This may be stuff that has not been proxied yet, yes - @juj can confirm.

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 7 days. Feel free to re-open at any time if this issue is still relevant.

[kripken]

Looks like the PR for this is #9336 - would be good to get that landed. @jakogut - is there something blocking it?

[jakogut]

@kripken No blockers, just have to address the feedback given. I can look at doing that later this week.

[thany-noroozpour]

Hi, is there any update for this issue?

[janpaul123]

For those coming across this, it looks like emscripten-ports/SDL2#127 is still open.

[SoapyMan]

So question is... when? 😅