New threads API index different then context after an eglMakeCurrent.

[Brandon Schaefer]

Say you have 2 threads A/B.

Thread A:
Starts running application, does an eglBindAPI(OPENGL), so the threads API index is 2
eglMakeCurrent(context) <--- The contexts API is 2
<renders stuff>
<start to swtich over to thread B>
eglMakeCurrent(EGL_NO_CONTEXT, EGL_NO_SURFACE) ... etc.

Thread B:
New thread created. Defaults the API index to OPENGL_ES. So the threads API index is 0.
eglcurrent.c:149: t->CurrentAPIIndex = _eglConvertApiToIndex(EGL_OPENGL_ES_API);

eglMakeCurrent(context) <--- The contexts API index is 2

--The Problem--
When it gets down to _eglBindContextToThread, it uses the contexts API index. So it binds the context to index 2, and returns TRUE.
On the next eglSwapBuffers, it does an _eglGetCurrentContext(), which uses the threads API index, which is 0. This returns an EGL_NO_CONTEXT (0x0), causing EGL_BAD_SURFACE, causing lots of other fun problems after. Mainly, after this happens, no rendering is possible.

_eglBindContextToThread:459 uses:
   apiIndex = (ctx) ?
      _eglConvertApiToIndex(ctx->ClientAPI) : t->CurrentAPIIndex;

To get the api index.

_eglGetCurrentContext:
   return t->CurrentContexts[t->CurrentAPIIndex];

So possibly, when a context is bound to a thread it should check if the threads api index != context api index, if so then set the threads api index to the contexts api index.

[Chris Halse Rogers (raof)]

So, reading the spec (specifically, section 3.7), I believe the current mesa behaviour is wrong and you should be perfectly able to eglMakeCurrent(context). Indeed, it looks like you should even be able to call SwapBuffers on thread 2 even without making a context current there.

However, I don't think the proposed solution is correct, either; as I read the spec we actually need the the context (and surface) to have a reference to their own API index, separate to the thread's API index - you can have multiple contexts of different APIs active on a same thread.

To the mesa devel lists!