[dxvk] Check whether CS thread is busy before synchronizing with it

Reduces unnecessary locking overhead, which may be relevant if this
function gets called frequently by GetData or WaitForResource.

src/d3d11/d3d11_context_imm.cpp

@@ -487,7 +487,8 @@ namespace dxvk {
     // recorded prior to this function will be run
     FlushCsChunk();
     
-    m_csThread.synchronize();
+    if (m_csThread.isBusy())
+      m_csThread.synchronize();
   }
   
   

src/dxvk/dxvk_cs.cpp

@@ -127,7 +127,7 @@ namespace dxvk {
     std::unique_lock<std::mutex> lock(m_mutex);
     
     m_condOnSync.wait(lock, [this] {
-      return m_chunksPending == 0;
+      return !m_chunksPending.load();
     });
   }
   

src/dxvk/dxvk_cs.h

@@ -407,6 +407,18 @@ namespace dxvk {
      */
     void synchronize();
     
+    /**
+     * \brief Checks whether the worker thread is busy
+     * 
+     * Note that this information is only reliable if
+     * only the calling thread dispatches jobs to the
+     * worker queue and if the result is \c false.
+     * \returns \c true if there is still work to do
+     */
+    bool isBusy() const {
+      return m_chunksPending.load() != 0;
+    }
+    
   private:
     
     const Rc<DxvkContext>       m_context;
@@ -416,10 +428,9 @@ namespace dxvk {
     std::condition_variable     m_condOnAdd;
     std::condition_variable     m_condOnSync;
     std::queue<DxvkCsChunkRef>  m_chunksQueued;
+    std::atomic<uint32_t>       m_chunksPending = { 0u };
     dxvk::thread                m_thread;
     
-    uint32_t                    m_chunksPending = 0;
-    
     void threadFunc();
     
   };