ProductBase.h

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#ifndef CUDADataFormats_Common_ProductBase_h
#define CUDADataFormats_Common_ProductBase_h

#include <atomic>
#include <memory>

#include "HeterogeneousCore/CUDAUtilities/interface/SharedStreamPtr.h"
#include "HeterogeneousCore/CUDAUtilities/interface/SharedEventPtr.h"

namespace cms {
  namespace cuda {
    namespace impl {
      class ScopedContextBase;
    }

    class ProductBase {
    public:
      ProductBase() = default;  // Needed only for ROOT dictionary generation
      ~ProductBase();

      ProductBase(const ProductBase&) = delete;
      ProductBase& operator=(const ProductBase&) = delete;
      ProductBase(ProductBase&& other)
          : stream_{std::move(other.stream_)},
            event_{std::move(other.event_)},
            mayReuseStream_{other.mayReuseStream_.load()},
            device_{other.device_} {}
      ProductBase& operator=(ProductBase&& other) {
        stream_ = std::move(other.stream_);
        event_ = std::move(other.event_);
        mayReuseStream_ = other.mayReuseStream_.load();
        device_ = other.device_;
        return *this;
      }

      bool isValid() const { return stream_.get() != nullptr; }
      bool isAvailable() const;

      int device() const { return device_; }

      // cudaStream_t is a pointer to a thread-safe object, for which a
      // mutable access is needed even if the cms::cuda::ScopedContext itself
      // would be const. Therefore it is ok to return a non-const
      // pointer from a const method here.
      cudaStream_t stream() const { return stream_.get(); }

      // cudaEvent_t is a pointer to a thread-safe object, for which a
      // mutable access is needed even if the cms::cuda::ScopedContext itself
      // would be const. Therefore it is ok to return a non-const
      // pointer from a const method here.
      cudaEvent_t event() const { return event_.get(); }

    protected:
      explicit ProductBase(int device, SharedStreamPtr stream, SharedEventPtr event)
          : stream_{std::move(stream)}, event_{std::move(event)}, device_{device} {}

    private:
      friend class impl::ScopedContextBase;
      friend class ScopedContextProduce;

      // The following function is intended to be used only from ScopedContext
      const SharedStreamPtr& streamPtr() const { return stream_; }

      bool mayReuseStream() const {
        bool expected = true;
        bool changed = mayReuseStream_.compare_exchange_strong(expected, false);
        // If the current thread is the one flipping the flag, it may
        // reuse the stream.
        return changed;
      }

      // The cudaStream_t is really shared among edm::Event products, so
      // using shared_ptr also here
      SharedStreamPtr stream_;  
      // shared_ptr because of caching in cms::cuda::EventCache
      SharedEventPtr event_;  

      // This flag tells whether the CUDA stream may be reused by a
      // consumer or not. The goal is to have a "chain" of modules to
      // queue their work to the same stream.
      mutable std::atomic<bool> mayReuseStream_ = true;  

      // The CUDA device associated with this product
      int device_ = -1;  
    };
  }  // namespace cuda
}  // namespace cms

#endif