src/dawn/native/RefCountedWithExternalCount.h

// Copyright 2022 The Dawn & Tint Authors
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#ifndef SRC_DAWN_NATIVE_REFCOUNTEDWITHEXTERNALCOUNT_H_
#define SRC_DAWN_NATIVE_REFCOUNTEDWITHEXTERNALCOUNT_H_

#include "dawn/common/RefCounted.h"

namespace dawn::native {

// RecCountedWithExternalCountBase is a version of RefCounted which tracks a separate
// refcount for calls to APIReference/APIRelease (refs added/removed by the application).
// The external refcount starts at 0, and the total refcount starts at 1 - i.e. the first
// ref isn't an external ref.
// When the external refcount drops to zero, WillDropLastExternalRef is called. and it can be called
// more than once.
// The derived class should override the behavior of WillDropLastExternalRef.
template <typename T>
class RefCountedWithExternalCountBase : public T {
  public:
    static constexpr bool HasExternalRefCount = true;

    using T::Reference;
    using T::Release;
    using T::T;

    void APIReference() {
        IncrementExternalRefCount();
        T::APIReference();
    }

    void APIRelease() {
        if (mExternalRefCount.Decrement()) {
            WillDropLastExternalRef();
        }
        T::APIRelease();
    }

    void IncrementExternalRefCount() { mExternalRefCount.Increment(); }

    uint64_t GetExternalRefCountForTesting() const {
        return mExternalRefCount.GetValueForTesting();
    }

  protected:
    using T::DeleteThis;

  private:
    virtual void WillDropLastExternalRef() = 0;

    RefCount mExternalRefCount{/*initCount=*/0, /*payload=*/0};
};

using RefCountedWithExternalCount = RefCountedWithExternalCountBase<RefCounted>;

}  // namespace dawn::native

#endif  // SRC_DAWN_NATIVE_REFCOUNTEDWITHEXTERNALCOUNT_H_