made savestates synchronous and immediate. this allows saving or loading while the emulator is paused, fixes issues where savestate hotkeys would get ignored if pressed too close together, might speed up savestates in some cases, and hopefully makes savestates more stable too.

the intent is to replace the haphazard scheduling and finger-crossing associated with saving/loading with the correct and minimal necessary wait for each thread to reach a known safe location before commencing the savestate operation, and for any already-paused components to not need to be resumed to do so.

Source/Core/VideoCommon/Src/Fifo.h

@@ -30,7 +30,9 @@ extern volatile bool g_bSkipCurrentFrame;
 
 void Fifo_Init();
 void Fifo_Shutdown();
+
 void Fifo_DoState(PointerWrap &f);
+void Fifo_PauseAndLock(bool doLock, bool unpauseOnUnlock);
 
 void ReadDataFromFifo(u8* _uData, u32 len);
 
@@ -45,6 +47,5 @@ void Fifo_SetRendering(bool bEnabled);
 
 // Implemented by the Video Backend
 void VideoFifo_CheckAsyncRequest();
-void VideoFifo_CheckStateRequest();
 
 #endif // _FIFO_H