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.