itkThreadPool.h

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/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef itkThreadPool_h
#define itkThreadPool_h
 
#include "itkConfigure.h"
#include "itkIntTypes.h"
 
#include <deque>
#include <functional>
#include <future>
#include <condition_variable>
#include <thread>
 
#include "itkObject.h"
#include "itkObjectFactory.h"
#include "itkSingletonMacro.h"
 
 
namespace itk
{

 
struct ThreadPoolGlobals;
 
class ITKCommon_EXPORT ThreadPool : public Object
{
public:
  ITK_DISALLOW_COPY_AND_MOVE(ThreadPool);

  using Self = ThreadPool;
  using Superclass = Object;
  using Pointer = SmartPointer<Self>;
  using ConstPointer = SmartPointer<const Self>;

  itkOverrideGetNameOfClassMacro(ThreadPool);

  static Pointer
  New();

  static Pointer
  GetInstance();

  template <class Function, class... Arguments>
  auto
  AddWork(Function && function, Arguments &&... arguments) -> std::future<std::invoke_result_t<Function, Arguments...>>
  {
    using return_type = std::invoke_result_t<Function, Arguments...>;
 
    auto task = std::make_shared<std::packaged_task<return_type()>>(
      [function, arguments...]() -> return_type { return function(arguments...); });
 
    std::future<return_type> res = task->get_future();
    {
      const std::lock_guard<std::mutex> lockGuard(this->GetMutex());
      m_WorkQueue.emplace_back([task]() { (*task)(); });
    }
    m_Condition.notify_one();
    return res;
  }

  void
  AddThreads(ThreadIdType count);
 
  ThreadIdType
  GetMaximumNumberOfThreads() const
  {
    const std::lock_guard<std::mutex> lockGuard(this->GetMutex());
    return static_cast<ThreadIdType>(m_Threads.size());
  }

  int
  GetNumberOfCurrentlyIdleThreads() const;

  static bool
  GetDoNotWaitForThreads();
  static void
  SetDoNotWaitForThreads(bool doNotWaitForThreads);
protected:
  std::mutex &
  GetMutex() const;
 
  ThreadPool();

  void
  CleanUp();
 
  ~ThreadPool() override { this->CleanUp(); }
 
  static void
  PrepareForFork();
  static void
  ResumeFromFork();
 
private:
  itkGetGlobalDeclarationMacro(ThreadPoolGlobals, PimplGlobals);

  std::deque<std::function<void()>> m_WorkQueue; // guarded by m_PimplGlobals->m_Mutex

  std::condition_variable m_Condition;

  std::vector<std::thread> m_Threads; // guarded by m_PimplGlobals->m_Mutex
 
  /* Has destruction started? */
  bool m_Stopping{ false }; // guarded by m_PimplGlobals->m_Mutex

  static ThreadPoolGlobals * m_PimplGlobals;

  static void
  ThreadExecute();
};
 
} // namespace itk
#endif