VideoCommon: Add AsyncShaderCompiler class implementation

Source/Core/VideoCommon/AsyncShaderCompiler.h

@@ -0,0 +1,83 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <atomic>
+#include <condition_variable>
+#include <deque>
+#include <functional>
+#include <memory>
+#include <mutex>
+#include <thread>
+#include <vector>
+
+#include "Common/CommonTypes.h"
+#include "Common/Event.h"
+#include "Common/Flag.h"
+
+namespace VideoCommon
+{
+class AsyncShaderCompiler
+{
+public:
+  class WorkItem
+  {
+  public:
+    virtual ~WorkItem() = default;
+    virtual bool Compile() = 0;
+    virtual void Retrieve() = 0;
+  };
+
+  using WorkItemPtr = std::unique_ptr<WorkItem>;
+
+  AsyncShaderCompiler();
+  virtual ~AsyncShaderCompiler();
+
+  template <typename T, typename... Params>
+  static WorkItemPtr CreateWorkItem(Params... params)
+  {
+    return std::unique_ptr<WorkItem>(new T(params...));
+  }
+
+  void QueueWorkItem(WorkItemPtr item);
+  void RetrieveWorkItems();
+  bool HasPendingWork();
+
+  // Simpler version without progress updates.
+  void WaitUntilCompletion();
+
+  // Calls progress_callback periodically, with completed_items, and total_items.
+  void WaitUntilCompletion(const std::function<void(size_t, size_t)>& progress_callback);
+
+  // Needed because of calling virtual methods in shutdown procedure.
+  void StartWorkerThreads(u32 num_worker_threads);
+  bool HasWorkerThreads() const;
+  void StopWorkerThreads();
+
+protected:
+  virtual bool WorkerThreadInitMainThread(void** param);
+  virtual bool WorkerThreadInitWorkerThread(void* param);
+  virtual void WorkerThreadExit(void* param);
+
+private:
+  void WorkerThreadEntryPoint(void* param);
+  void WorkerThreadRun();
+
+  Common::Flag m_exit_flag;
+  Common::Event m_init_event;
+
+  std::vector<std::thread> m_worker_threads;
+  std::atomic_bool m_worker_thread_start_result{false};
+
+  std::deque<WorkItemPtr> m_pending_work;
+  std::mutex m_pending_work_lock;
+  std::condition_variable m_worker_thread_wake;
+  std::atomic_size_t m_busy_workers{0};
+
+  std::deque<WorkItemPtr> m_completed_work;
+  std::mutex m_completed_work_lock;
+};
+
+}  // namespace VideoCommon