AtomicCache.h

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#ifndef VolViz_AtomicCache_h
#define VolViz_AtomicCache_h

#include <gsl/gsl>

#include <atomic>

#pragma clang diagnostic ignored "-Wpadded"

namespace VolViz {

template <class T> class AtomicCache {
public:
  template <class FetchOp>
  AtomicCache(FetchOp fetchOperation)
      : fetchOperation_(fetchOperation) {
    Expects(fetchOperation_);
    dirtyFlag_.clear();
  }

  inline void markAsDirty() noexcept { dirtyFlag_.clear(); }

  inline operator T const &() const noexcept {
    if (dirtyFlag_.test_and_set()) return value_;

    Expects(fetchOperation_);
    value_ = std::move(fetchOperation_());
    return value_;
  }

private:
  mutable T value_;

  mutable std::atomic_flag dirtyFlag_;

  std::function<T()> const fetchOperation_;
};

} // namespace VolViz

#endif // VolViz_AtomicCache_h