itkThreadPool.h

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/*=========================================================================
 *
 *  Copyright Insight Software Consortium
 *
 *  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
 *
 *         http://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_ASSIGN(ThreadPool);

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

  itkTypeMacro(ThreadPool, Object);

  static Pointer New();

  static Pointer GetInstance();

  template< class Function, class... Arguments >
  auto
  AddWork( Function&& function, Arguments&&... arguments )
    -> std::future< typename std::result_of< Function( Arguments... ) >::type >
  {
    using return_type = typename std::result_of< Function( Arguments... ) >::type;

    auto task = std::make_shared< std::packaged_task< return_type() > >(
      std::bind( std::forward< Function >( function ), std::forward< Arguments >( arguments )... ) );

    std::future< return_type > res = task->get_future();
    {
      std::unique_lock< std::mutex > lock( this->GetMutex() );
      m_WorkQueue.emplace_back( [task]() { ( *task )(); } );
    }
    m_Condition.notify_one();
    return res;
  }

  void AddThreads(ThreadIdType count);

  ThreadIdType GetMaximumNumberOfThreads() const
  {
    return static_cast< ThreadIdType >( m_Threads.size() );
  }

  int GetNumberOfCurrentlyIdleThreads() const;

  static bool GetDoNotWaitForThreads();
  static void SetDoNotWaitForThreads(bool doNotWaitForThreads);

protected:

  /* We need access to the mutex in AddWork, and the variable is only
   * visible in .cxx file, so this method returns it. */
  std::mutex& GetMutex();

  ThreadPool();
  ~ThreadPool() override;

private:

  itkGetGlobalDeclarationMacro(ThreadPoolGlobals, PimplGlobals);

  std::deque< std::function< void() > > m_WorkQueue;

  std::condition_variable m_Condition;

  std::vector< std::thread > m_Threads;

  /* Has destruction started? */
  bool m_Stopping{ false };

  static ThreadPoolGlobals * m_PimplGlobals;

  static void ThreadExecute();
};

}
#endif