connect_but_block_self.h

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#ifndef ServiceRegistry_connect_but_block_self_h
#define ServiceRegistry_connect_but_block_self_h
// -*- C++ -*-
//
// Package:     ServiceRegistry
// Class  :     connect_but_block_self
//
//
// Original Author:  Chris Jones
//         Created:  Thu Sep 22 20:42:32 CEST 2005
//

// system include files
#include <memory>
#include "FWCore/Utilities/interface/Signal.h"

// user include files

// forward declarations
namespace edm {
  namespace serviceregistry {
    template <typename Func>
    class BlockingWrapper {
    public:
      BlockingWrapper(Func iFunc) : func_(iFunc), numBlocks_(0) {}
      //virtual ~BlockingWrapper();

      // ---------- const member functions ---------------------
      template <typename... Args>
      void operator()(Args&&... args) {
        std::shared_ptr<void> guard(static_cast<void*>(nullptr), std::bind(&BlockingWrapper::unblock, this));
        if (startBlocking()) {
          func_(std::forward<Args>(args)...);
        }
      }

      // ---------- static member functions --------------------

      // ---------- member functions ---------------------------

    private:
      // ---------- member data --------------------------------
      bool startBlocking() { return 1 == ++numBlocks_; }
      void unblock() { --numBlocks_; }
      Func func_;
      int numBlocks_;
    };

    template <class Func, class Signal>
    void connect_but_block_self(Signal& oSignal, const Func& iFunc) {
      oSignal.connect(BlockingWrapper<Func>(iFunc));
    }
  }  // namespace serviceregistry
}  // namespace edm

#endif