FiberManager.h

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* (c) Copyright 1998-2024 CERN for the benefit of the LHCb and ATLAS collaborations *
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* This software is distributed under the terms of the Apache version 2 licence,     *
* copied verbatim in the file "LICENSE".                                            *
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#pragma once
 
#include <boost/fiber/algo/shared_work.hpp>
#include <boost/fiber/condition_variable.hpp>
#include <boost/fiber/fiber.hpp>
#include <boost/fiber/mutex.hpp>
 
#include <fmt/format.h>
 
class FiberManager {
public:
  FiberManager( int n_threads ) {
    for ( int i = 0; i < n_threads; ++i ) {
      m_threads.emplace_back( std::thread( [this]() {
        boost::fibers::use_scheduling_algorithm<boost::fibers::algo::shared_work>( true );
        std::unique_lock lck{ m_shuttingDown_mtx };
        m_shuttingDown_cv.wait( lck );
      } ) );
    }
  }
 
  ~FiberManager() {
    m_shuttingDown_cv.notify_all();
 
    for ( std::thread& t : m_threads ) { t.join(); }
  }
 
  template <typename F>
  void schedule( F&& func ) {
    if ( !m_activated ) {
      // Since we never call boost::this_fiber::yield, fibers never actually run on this thread
      boost::fibers::use_scheduling_algorithm<boost::fibers::algo::shared_work>( true );
      m_activated = true;
    }
    boost::fibers::fiber( boost::fibers::launch::post, std::forward<F>( func ) ).detach();
  }
 
private:
  boost::fibers::condition_variable m_shuttingDown_cv{};
  boost::fibers::mutex              m_shuttingDown_mtx{};
  std::vector<std::thread>          m_threads;
  bool                              m_activated = false; // set to true when first fiber is scheduled
};