Common: add WorkQueueThread

Source/Core/Common/Common.vcxproj

@@ -152,6 +152,7 @@
     <ClInclude Include="TraversalClient.h" />
     <ClInclude Include="TraversalProto.h" />
     <ClInclude Include="UPnP.h" />
+    <ClInclude Include="WorkQueueThread.h" />
     <ClInclude Include="x64ABI.h" />
     <ClInclude Include="x64Emitter.h" />
     <ClInclude Include="x64Reg.h" />

Source/Core/Common/Common.vcxproj.filters

@@ -68,6 +68,7 @@
     <ClInclude Include="SysConf.h" />
     <ClInclude Include="Thread.h" />
     <ClInclude Include="Timer.h" />
+    <ClInclude Include="WorkQueueThread.h" />
     <ClInclude Include="x64ABI.h" />
     <ClInclude Include="x64Emitter.h" />
     <ClInclude Include="x64Reg.h" />

Source/Core/Common/WorkQueueThread.h

@@ -0,0 +1,86 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <functional>
+#include <queue>
+#include <thread>
+
+#include "Common/Event.h"
+#include "Common/Flag.h"
+
+// A thread that executes the given function for every item placed into its queue.
+
+namespace Common
+{
+template <typename T>
+class WorkQueueThread
+{
+public:
+  WorkQueueThread() = default;
+  WorkQueueThread(std::function<void(T)> function) { Reset(std::move(function)); }
+  ~WorkQueueThread() { Shutdown(); }
+  void Reset(std::function<void(T)> function)
+  {
+    Shutdown();
+    m_shutdown.Clear();
+    m_function = std::move(function);
+    m_thread = std::thread([this] { ThreadLoop(); });
+  }
+
+  template <typename... Args>
+  void EmplaceItem(Args&&... args)
+  {
+    {
+      std::unique_lock<std::mutex> lg(m_lock);
+      m_items.emplace(std::move(args)...);
+    }
+    m_wakeup.Set();
+  }
+
+private:
+  void Shutdown()
+  {
+    if (m_thread.joinable())
+    {
+      m_shutdown.Set();
+      m_wakeup.Set();
+      m_thread.join();
+    }
+  }
+
+  void ThreadLoop()
+  {
+    while (true)
+    {
+      m_wakeup.Wait();
+
+      while (true)
+      {
+        T item;
+        {
+          std::unique_lock<std::mutex> lg(m_lock);
+          if (m_items.empty())
+            break;
+          item = m_items.front();
+          m_items.pop();
+        }
+        m_function(std::move(item));
+      }
+
+      if (m_shutdown.IsSet())
+        break;
+    }
+  }
+
+  std::function<void(T)> m_function;
+  std::thread m_thread;
+  Common::Event m_wakeup;
+  Common::Flag m_shutdown;
+  std::mutex m_lock;
+  std::queue<T> m_items;
+};
+
+}  // namespace Common