WorkQueueThread: Rework without Flags/Events

Source/Core/Common/WorkQueueThread.h

@@ -25,8 +25,8 @@ public:
   void Reset(std::function<void(T)> function)
   {
     Shutdown();
-    m_shutdown.Clear();
-    m_cancelled.Clear();
+    std::lock_guard lg(m_lock);
+    m_cancelled = false;
     m_function = std::move(function);
     m_thread = std::thread(&WorkQueueThread::ThreadLoop, this);
   }
@@ -34,85 +34,107 @@ public:
   template <typename... Args>
   void EmplaceItem(Args&&... args)
   {
-    if (!m_cancelled.IsSet())
+    std::lock_guard lg(m_lock);
+    if (m_shutdown)
     {
-      std::lock_guard lg(m_lock);
-      m_items.emplace(std::forward<Args>(args)...);
+      return;
     }
-    m_wakeup.Set();
+    m_items.emplace(std::forward<Args>(args)...);
+    m_idle = false;
+    m_worker_cond_var.notify_one();
   }
 
   void Push(T&& item)
   {
-    if (!m_cancelled.IsSet())
+    std::lock_guard lg(m_lock);
+    if (m_cancelled)
     {
-      std::lock_guard lg(m_lock);
-      m_items.push(item);
+      return;
     }
-    m_wakeup.Set();
+    m_items.push(item);
+    m_idle = false;
+    m_worker_cond_var.notify_one();
   }
 
   void Push(const T& item)
   {
-    if (!m_cancelled.IsSet())
-    {
       std::lock_guard lg(m_lock);
+      if (m_cancelled)
+      {
+        return;
+      }
       m_items.push(item);
-    }
-    m_wakeup.Set();
+      m_idle = false;
+      m_worker_cond_var.notify_one();
   }
 
   void Clear()
   {
-    {
-      std::lock_guard lg(m_lock);
-      m_items = std::queue<T>();
-    }
-    m_wakeup.Set();
+    std::lock_guard lg(m_lock);
+    m_items = std::queue<T>();
+    m_worker_cond_var.notify_one();
   }
 
   void Cancel()
   {
-    m_cancelled.Set();
-    Clear();
-    Shutdown();
-  }
+    if (!m_thread.joinable())
+    {
+      return;
+    }
 
-  bool IsCancelled() const { return m_cancelled.IsSet(); }
+    {
+      std::unique_lock lg(m_lock);
+      m_items = std::queue<T>();
+      m_cancelled = true;
+      m_shutdown = true;
+      m_worker_cond_var.notify_one();
+    }
+    m_thread.join();
+  }
 
   void Shutdown()
   {
-    if (m_thread.joinable())
+    if (!m_thread.joinable())
     {
-      m_shutdown.Set();
-      m_wakeup.Set();
-      m_thread.join();
+      return;
     }
+
+    {
+      std::unique_lock lg(m_lock);
+      m_shutdown = true;
+      m_worker_cond_var.notify_one();
+    }
+    m_thread.join();
   }
 
   // Doesn't return until the most recent function invocation has finished.
-  void FlushOne()
+  void ClearAndFlush()
   {
-    if (m_thread.joinable())
+    if (!m_thread.joinable())
     {
-      m_flush.Set();
-      Clear();
-      m_flushed.Wait();
+      return;
     }
+
+    std::unique_lock lg(m_lock);
+    m_items = std::queue<T>();
+    m_wait_cond_var.wait(lg, [&] {
+        return m_idle;
+    });
   }
 
-  // Doesn't return until the queue is empty.
+  // Doesn't return until the most recent function invocation has finished.
   void Flush()
   {
-    if (m_thread.joinable())
+    if (!m_thread.joinable())
     {
-      m_flush.Set();
-      m_wakeup.Set();
-      m_flushed.Wait();
+      return;
     }
-  }
 
-  bool IsFlushing() const { return m_flush.IsSet() || m_shutdown.IsSet(); }
+    std::unique_lock lg(m_lock);
+    m_wait_cond_var.wait(lg, [&] {
+        return m_idle;
+    });
+  }
 
 private:
   void ThreadLoop()
@@ -121,41 +143,37 @@ private:
 
     while (true)
     {
-      m_wakeup.Wait();
-
-      while (true)
+      std::unique_lock lg(m_lock);
+      if (m_items.empty())
       {
-        std::unique_lock lg(m_lock);
-        if (m_items.empty())
+        m_idle = true;
+        m_wait_cond_var.notify_all();
+        m_worker_cond_var.wait(lg, [&] {
+            return m_shutdown || !m_items.empty();
+        });
+        if (m_shutdown)
         {
-          if (m_flush.IsSet())
-          {
-            m_flush.Clear();
-            m_flushed.Set();
-          }
           break;
         }
-        T item{std::move(m_items.front())};
-        m_items.pop();
-        lg.unlock();
-
-        m_function(std::move(item));
+        continue;
       }
+      T item{std::move(m_items.front())};
+      m_items.pop();
+      lg.unlock();
 
-      if (m_shutdown.IsSet())
-        break;
+      m_function(std::move(item));
     }
   }
 
   std::function<void(T)> m_function;
   std::thread m_thread;
-  Common::Event m_wakeup;
-  Common::Flag m_shutdown;
-  Common::Flag m_cancelled;
-  Common::Flag m_flush;
-  Common::Event m_flushed;
   std::mutex m_lock;
   std::queue<T> m_items;
+  std::condition_variable m_wait_cond_var;
+  std::condition_variable m_worker_cond_var;
+  bool m_idle = true;
+  bool m_shutdown = false;
+  bool m_cancelled = false;
 };
 
 }  // namespace Common