Further discussion about threading and overlays

[vanfanel]

Hi there,

I am opening this to discuss the use of this as a workaround for the several seconds stalls in DL2:

hypseus/src/video/video.cpp

Line 710 in c2d4dea

SDL_CondWaitTimeout(g_yuv_surface->pending_update_cond, g_yuv_surface->mutex, 100);

Original PR:

#24

Original analysis by @lmerckx is copied here for convenience:

Some games (bega, astron, ...) freezes during some seconds and restart after a timeout message VLDP error! Timed out waiting for internal thread to accept command!:
This problems seems due to the "lock" system between methods vid_blit and vid_update_yuv_overlay.
Indeed, these methods use SDL_CondWait and SDL_CondSignal to avoid conflict when changing same texture.
But for these games, vid_update_yuv_overlay is called twice (setting vid_update_yuv_overlay to true) without any call to vid_blit.
It leads in a blocking call to vid_update_yuv_overlay, which also blocks the command handler; and avoid processing other command.
Only the timeout, after about 7 seconds, unblocks the emulator.
So, I replace SDL_CondWait by SDL_CondWaitTimeout (with a timeout of 100 ms) to solve the problem.

The blocking should not happen to start with. This seems like a workaround and not a true solution. Any ideas?

[lmerckx]

Indeed, I'm not very proud of this workaround.

As you say, the proper way could be to avoid calling twice the method "vid_update_yuv_overlay" but I didn't find how to do that previously.
Now, it's very far from my memory :)

[vanfanel]

@lmerckx @h0tw1r3 What's the game trying to archieve if it calls vid_update_yuv_overlay and does not call vid_blit?

My understanding is that all games should call vid_blit to show something on screen, be it a FMV frame and/or superinposed info like sprites or scoreboards, right?

Maybe I should simply let the games call vid_update_yuv_overlay unconditionally without waiting for a vid_blit call?

Maybe I am misunderstanding the internal architecture of the program here...

@h0tw1r3 I know you are busy but I need your input about this too.

[vanfanel]

In other words: there MUST be a "central" function that calls SDL_RenderPresent, and that function is, from my understanding, vid_blit.

A game can update the YUV surface (via vid_update_yuv_overlay) but that doesn't send the YUV surface contents to the screen: that has to be done in vid_blit.

That or I just don't get how hypseus is supposed to present the video.

[vanfanel]

Well, in the end I decided to disable waiting for texture updates for now.
If a game wants to update the YUV surface but doesn't want the video to be blit immediately, so be it.
It will prevent the VLDP thread to get stuck, at least. I didn't see any caveats, so here it goes, please merge:
#33