Band-Aid for libretro Savestate load

[m4xw]

Proper would be using PPSSPP's Queue.
This will need frontend extensions to do it sanely.
Fixes #11429 (mitigate for now)

[unknownbrackets]

Hmm looking at this again, I'd suggest using Core_EnableStepping. That would work on all backends. Stepping is in other words debugging, and while debugging the CPU is paused regardless of thread behavior.

Example:

static serializeWasStepping = false;

size_t retro_serialize_size(void) {
	serializeWasStepping = Core_IsStepping();
	Core_EnableStepping(true);
	// If we're on the CPU thread actually, this may just stall for 16ms...
	Core_WaitInactive(16);

	// Intentionally leaving in stepping.
	// TODO: Not sure if 0x800000 alignment is necessary (that's 8MB.)
	return CChunkFileReader::MeasurePtr(state);
}

bool retro_serialize(void *data, size_t size) {
	if (Core_IsActive()) {
		ERROR_LOG(SYSTEM, "retro_serialize_size() must be called before retro_serialize()");
		return false;
	}
	if (size < CChunkFileReader::MeasurePtr(state)) {
		ERROR_LOG(SYSTEM, "retro_serialize() called with too small a size");
		return false;
	}

	bool retVal = CChunkFileReader::SavePtr(...);

	if (!serializeWasStepping) {
		Core_EnableStepping(false);
		// No need to wait for active, it'll resume on its own.
	}

	return retVal;
}

That said, probably doing this thread pausing stuff will work too, at least for GL. Would have to save the std::thread id or something and compare to know if Core_WaitInactive needs to be called, I suppose.

-[Unknown]

[hrydgard]

Merging as-is because the workaround apparently is highly in demand - @m4xw has promised to try and switch to EnableStepping later.

[orbea]

@m4xw Thanks a lot for taking time to work on ppsspp issues!

[NeoNight1986]

I am pretty confused, what do I need to do to fix the safe state freezing?