WaitingTaskWithArenaHolder.h

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#ifndef FWCore_Concurrency_WaitingTaskWithArenaHolder_h
#define FWCore_Concurrency_WaitingTaskWithArenaHolder_h
// -*- C++ -*-
//
// Package:     FWCore/Concurrency
// Class  :     WaitingTaskWithArenaHolder
//
//
// Original Author:  W. David Dagenhart
//         Created:  9 November 2017
//

#include <exception>
#include <memory>

#include "tbb/task_arena.h"

namespace edm {

  class WaitingTask;
  class WaitingTaskHolder;

  class WaitingTaskWithArenaHolder {
  public:
    WaitingTaskWithArenaHolder();

    // Note that the arena will be the one containing the thread
    // that runs this constructor. This is the arena where you
    // eventually intend for the task to be spawned.
    explicit WaitingTaskWithArenaHolder(WaitingTask* iTask);

    ~WaitingTaskWithArenaHolder();

    WaitingTaskWithArenaHolder(WaitingTaskWithArenaHolder const& iHolder);

    WaitingTaskWithArenaHolder(WaitingTaskWithArenaHolder&& iOther);

    WaitingTaskWithArenaHolder& operator=(const WaitingTaskWithArenaHolder& iRHS);

    WaitingTaskWithArenaHolder& operator=(WaitingTaskWithArenaHolder&& iRHS);

    // This spawns the task. The arena is needed to get the task spawned
    // into the correct arena of threads. Use of the arena allows doneWaiting
    // to be called from a thread outside the arena of threads that will manage
    // the task. doneWaiting can be called from a non-TBB thread.
    void doneWaiting(std::exception_ptr iExcept);

    // This next function is useful if you know from the context that
    // m_arena (which is set when the constructor was executes) is the
    // same arena in which you want to execute the doneWaiting function.
    // It allows an optimization which avoids the enqueue step in the
    // doneWaiting function.
    //
    // Be warned though that in general this function cannot be used.
    // Spawning a task outside the correct arena could create a new separate
    // arena with its own extra TBB worker threads if this function is used
    // in an inappropriate context (and silently such that you might not notice
    // the problem quickly).
    WaitingTaskHolder makeWaitingTaskHolderAndRelease();

  private:
    // ---------- member data --------------------------------
    WaitingTask* m_task;
    std::shared_ptr<tbb::task_arena> m_arena;
  };
}  // namespace edm
#endif