VideoCommon: Clean up and eliminate the mutex in AsyncRequests using WaitableSPSCQueue.

Source/Core/VideoCommon/AsyncRequests.cpp

@@ -3,8 +3,6 @@
 
 #include "VideoCommon/AsyncRequests.h"
 
-#include <mutex>
-
 #include "Core/System.h"
 
 #include "VideoCommon/Fifo.h"
@@ -16,33 +14,25 @@ AsyncRequests AsyncRequests::s_singleton;
 
 AsyncRequests::AsyncRequests() = default;
 
-void AsyncRequests::PullEventsInternal()
+void AsyncRequests::PullEvents()
 {
+  if (m_queue.Empty())
+    return;
+
   // This is only called if the queue isn't empty.
   // So just flush the pipeline to get accurate results.
   g_vertex_manager->Flush();
 
-  std::unique_lock<std::mutex> lock(m_mutex);
-  m_empty.Set();
-
-  while (!m_queue.empty())
+  while (!m_queue.Empty())
   {
-    Event e = std::move(m_queue.front());
-    lock.unlock();
-    std::invoke(e);
-    lock.lock();
-
-    m_queue.pop();
+    std::invoke(std::move(m_queue.Front()));
+    m_queue.Pop();
   }
-
-  m_cond.notify_one();
 }
 
 void AsyncRequests::QueueEvent(Event&& event)
 {
-  m_empty.Clear();
-
-  m_queue.push(std::move(event));
+  m_queue.Push(std::move(event));
 
   auto& system = Core::System::GetInstance();
   system.GetFifo().RunGpu();
@@ -50,12 +40,10 @@ void AsyncRequests::QueueEvent(Event&& event)
 
 void AsyncRequests::WaitForEmptyQueue()
 {
-  std::unique_lock<std::mutex> lock(m_mutex);
-  m_cond.wait(lock, [this] { return m_queue.empty(); });
+  m_queue.WaitForEmpty();
 }
 
 void AsyncRequests::SetPassthrough(bool enable)
 {
-  std::unique_lock<std::mutex> lock(m_mutex);
   m_passthrough = enable;
 }

Source/Core/VideoCommon/AsyncRequests.h

@@ -3,14 +3,12 @@
 
 #pragma once
 
-#include <condition_variable>
+#include <concepts>
 #include <functional>
 #include <future>
-#include <mutex>
-#include <queue>
 
-#include "Common/Flag.h"
 #include "Common/Functional.h"
+#include "Common/SPSCQueue.h"
 
 struct EfbPokeData;
 class PointerWrap;
@@ -20,43 +18,39 @@ class AsyncRequests
 public:
   AsyncRequests();
 
-  void PullEvents()
-  {
-    if (!m_empty.IsSet())
-      PullEventsInternal();
-  }
-  void WaitForEmptyQueue();
-  void SetPassthrough(bool enable);
+  // Called from the Video thread.
+  void PullEvents();
 
-  template <typename F>
+  // The following are called from the CPU thread.
+  void WaitForEmptyQueue();
+
+  template <std::invocable<> F>
   void PushEvent(F&& callback)
   {
-    std::unique_lock<std::mutex> lock(m_mutex);
-
     if (m_passthrough)
     {
-      std::invoke(callback);
+      std::invoke(std::forward<F>(callback));
       return;
     }
 
     QueueEvent(Event{std::forward<F>(callback)});
   }
 
-  template <typename F>
+  template <std::invocable<> F>
   auto PushBlockingEvent(F&& callback) -> std::invoke_result_t<F>
   {
-    std::unique_lock<std::mutex> lock(m_mutex);
-
     if (m_passthrough)
-      return std::invoke(callback);
+      return std::invoke(std::forward<F>(callback));
 
     std::packaged_task task{std::forward<F>(callback)};
     QueueEvent(Event{[&] { task(); }});
 
-    lock.unlock();
     return task.get_future().get();
   }
 
+  // Not thread-safe. Only set during initialization.
+  void SetPassthrough(bool enable);
+
   static AsyncRequests* GetInstance() { return &s_singleton; }
 
 private:
@@ -64,14 +58,9 @@ private:
 
   void QueueEvent(Event&& event);
 
-  void PullEventsInternal();
-
   static AsyncRequests s_singleton;
 
-  Common::Flag m_empty;
-  std::queue<Event> m_queue;
-  std::mutex m_mutex;
-  std::condition_variable m_cond;
+  Common::WaitableSPSCQueue<Event> m_queue;
 
   bool m_passthrough = true;
 };