Reworked FenceGLImpl to use std::atomic

2 files changed, 22 insertions, 10 deletions

diff --git a/Graphics/GraphicsEngineOpenGL/include/FenceGLImpl.hpp b/Graphics/GraphicsEngineOpenGL/include/FenceGLImpl.hpp
index 108a676d..bd2a78a4 100644
--- a/Graphics/GraphicsEngineOpenGL/include/FenceGLImpl.hpp
+++ b/Graphics/GraphicsEngineOpenGL/include/FenceGLImpl.hpp
@@ -31,6 +31,8 @@
 /// Declaration of Diligent::FenceGLImpl class
 
 #include <deque>
+#include <atomic>
+
 #include "FenceGL.h"
 #include "RenderDeviceGL.h"
 #include "FenceBase.hpp"
@@ -67,8 +69,12 @@ public:
     void Wait(Uint64 Value, bool FlushCommands);
 
 private:
+    void UpdateFenceValue(Uint64 NewValue);
+
+private:
     std::deque<std::pair<Uint64, GLObjectWrappers::GLSyncObj>> m_PendingFences;
-    volatile Uint64                                            m_LastCompletedFenceValue = 0;
+
+    std::atomic_uint64_t m_LastCompletedFenceValue{0};
 };
 
 } // namespace Diligent
diff --git a/Graphics/GraphicsEngineOpenGL/src/FenceGLImpl.cpp b/Graphics/GraphicsEngineOpenGL/src/FenceGLImpl.cpp
index 78c840f1..ce23b5c9 100644
--- a/Graphics/GraphicsEngineOpenGL/src/FenceGLImpl.cpp
+++ b/Graphics/GraphicsEngineOpenGL/src/FenceGLImpl.cpp
@@ -51,6 +51,15 @@ FenceGLImpl::~FenceGLImpl()
 {
 }
 
+void FenceGLImpl::UpdateFenceValue(Uint64 NewValue)
+{
+    auto CurrValue = m_LastCompletedFenceValue.load();
+    while (!m_LastCompletedFenceValue.compare_exchange_strong(CurrValue, std::max(CurrValue, NewValue)))
+    {
+        // If exchange fails, CurrValue will hold the actual value of m_LastCompletedFenceValue
+    }
+}
+
 Uint64 FenceGLImpl::GetCompletedValue()
 {
     while (!m_PendingFences.empty())
@@ -64,8 +73,7 @@ Uint64 FenceGLImpl::GetCompletedValue()
             );
         if (res == GL_ALREADY_SIGNALED)
         {
-            if (val_fence.first > m_LastCompletedFenceValue)
-                m_LastCompletedFenceValue = val_fence.first;
+            UpdateFenceValue(val_fence.first);
             m_PendingFences.pop_front();
         }
         else
@@ -74,7 +82,7 @@ Uint64 FenceGLImpl::GetCompletedValue()
         }
     }
 
-    return m_LastCompletedFenceValue;
+    return m_LastCompletedFenceValue.load();
 }
 
 void FenceGLImpl::Wait(Uint64 Value, bool FlushCommands)
@@ -89,17 +97,15 @@ void FenceGLImpl::Wait(Uint64 Value, bool FlushCommands)
         VERIFY_EXPR(res == GL_ALREADY_SIGNALED || res == GL_CONDITION_SATISFIED);
         (void)res;
 
-        if (val_fence.first > m_LastCompletedFenceValue)
-            m_LastCompletedFenceValue = val_fence.first;
+        UpdateFenceValue(val_fence.first);
         m_PendingFences.pop_front();
     }
 }
 
-void FenceGLImpl::Reset(Uint64 Value)
+void FenceGLImpl::Reset(Uint64 NewValue)
 {
-    DEV_CHECK_ERR(Value >= m_LastCompletedFenceValue, "Resetting fence '", m_Desc.Name, "' to the value (", Value, ") that is smaller than the last completed value (", m_LastCompletedFenceValue, ")");
-    if (Value > m_LastCompletedFenceValue)
-        m_LastCompletedFenceValue = Value;
+    DEV_CHECK_ERR(NewValue >= m_LastCompletedFenceValue, "Resetting fence '", m_Desc.Name, "' to the value (", NewValue, ") that is smaller than the last completed value (", m_LastCompletedFenceValue, ")");
+    UpdateFenceValue(NewValue);
 }
 
 } // namespace Diligent