CallOnceNoWait.h

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#ifndef FWCore_Utilities_CallOnceNoWait_h
#define FWCore_Utilities_CallOnceNoWait_h
// -*- C++ -*-
//
// Package:     FWCore/Utilities
// Class  :     CallOnceNoWait
//
//
// Original Author:  Chris Jones
//         Created:  Fri, 15 Nov 2013 14:29:51 GMT
//

// system include files
#include <atomic>

// user include files

// forward declarations

namespace edm {
  class CallOnceNoWait {
  public:
    CallOnceNoWait() : m_called(false) {}

    template <typename T>
    void operator()(T iCall) {
      bool expected = false;
      if (m_called.compare_exchange_strong(expected, true, std::memory_order_acq_rel)) {
        iCall();
      }
    }

  private:
    std::atomic<bool> m_called;
  };
}  // namespace edm

#endif