CPU thread can run ahead of GPU thread too much

[taisel]

We need to add a check to futexWait the emulation core thread if the gfx thread is reporting a line counter lagging too far behind the command buffer's own line counter value. I haven't seen this issue happen at all, because CPU emulation is more heavyweight than the graphics thread, but I just want to add this check to be safe due to how it theoretically can occur.

[taisel]

We specifically designed around the cpu emulation running in parallel and slighty ahead of the gpu emulation, but we need to set hard limits. We do have a limit, but it's the size of the command buffer queue, which should really never ever be filled fully ever. I'd say 2 frames worth of counter incrementation is a nice hard limit we should add.*

*I say 2 and not 1 because we support triple buffering by design.

[taisel]

We specifically designed around the cpu emulation running in parallel and slighty ahead of the gpu emulation, but we need to set hard limits. We do have a limit, but it's the size of the command buffer queue, which should really never ever be filled fully ever. I'd say 2 frames worth of counter incrementation is a nice hard limit we should add.*

*I say 2 and not 1 because we support triple buffering by design.