CompositorBase: Remove frame locking for now.

This resulted in undefined behaviour due to UE4 sometimes calling EndFrame from a different thread than BeginFrame.

Author: CrossVR

Revive/CompositorBase.cpp

@@ -61,7 +61,6 @@ CompositorBase::CompositorBase()
 , m_OverlayCount(0)
 , m_ActiveOverlays()
 , m_FrameMutex()
-, m_FrameLock(m_FrameMutex, std::defer_lock)
 , m_FrameEvent()
 {
 // We want to handle all graphics tasks explicitly instead of implicitly letting WaitGetPoses execute them
@@ -121,7 +120,6 @@ ovrResult CompositorBase::WaitToBeginFrame(ovrSession session, long long frameIn
 MICROPROFILE_SCOPE(WaitToBeginFrame);
 
 // Protect the wait order with a mutex
-// This also waits for any frame still in-flight
 std::unique_lock<std::mutex> lk(m_FrameMutex);
 
 // Wait for any extra frames beyond just the next frame
@@ -140,11 +138,6 @@ ovrResult CompositorBase::WaitToBeginFrame(ovrSession session, long long frameIn
 ovrResult CompositorBase::BeginFrame(ovrSession session, long long frameIndex)
 {
 MICROPROFILE_SCOPE(BeginFrame);
-
-// Lock the frame mutex only if we don't already own it
-if (!m_FrameLock)
-m_FrameLock.lock();
-
 session->FrameIndex = frameIndex;
 vr::VRCompositor()->SubmitExplicitTimingData();
 return session->Input->UpdateInputState();
@@ -255,8 +248,6 @@ ovrResult CompositorBase::EndFrame(ovrSession session, ovrLayerHeader const * co
 
 // Frame now completed so we can let anyone waiting on the next frame call WaitGetPoses
 m_FrameEvent.notify_all();
-if (m_FrameLock)
-m_FrameLock.unlock();
 
 if (m_MirrorTexture && error == vr::VRCompositorError_None)
 RenderMirrorTexture(m_MirrorTexture);

Revive/CompositorBase.h

@@ -52,6 +52,5 @@ class CompositorBase
 
 // Call order enforcement
 std::mutex m_FrameMutex;
-std::unique_lock<std::mutex> m_FrameLock;
 std::condition_variable m_FrameEvent;
 };