EmuWindow::PollEvents was called from the GPU thread (or the CPU thread
in sync-GPU mode) when swapping buffers. It had three implementations:
- In GRenderWindow, it didn't actually poll events, just set a flag and
emit a signal to indicate that a frame was displayed.
- In EmuWindow_SDL2_Hide, it did nothing.
- In EmuWindow_SDL2, it did call SDL_PollEvents, but this is wrong
because SDL_PollEvents is supposed to be called on the thread that set
up video - in this case, the main thread, which was sleeping in a
busyloop (regardless of whether sync-GPU was enabled). On macOS this
causes a crash.
To fix this:
- Rename EmuWindow::PollEvents to OnFrameDisplayed, and give it a
default implementation that does nothing.
- In EmuWindow_SDL2, do not override OnFrameDisplayed, but instead have
the main thread call SDL_WaitEvent in a loop.
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