src/dawn/common/RefCounted.h

// Copyright 2017 The Dawn & Tint Authors
//
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// modification, are permitted provided that the following conditions are met:
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//    list of conditions and the following disclaimer.
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//    this list of conditions and the following disclaimer in the documentation
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#ifndef SRC_DAWN_COMMON_REFCOUNTED_H_
#define SRC_DAWN_COMMON_REFCOUNTED_H_

#include <atomic>
#include <cstdint>

namespace dawn {

namespace detail {
class WeakRefData;
}  // namespace detail

class RefCount {
  public:
    RefCount(uint64_t initCount, uint64_t payload);

    // Create a refcount with a payload. The refcount starts initially at one.
    explicit RefCount(uint64_t payload = 0);

    uint64_t GetValueForTesting() const;
    uint64_t GetPayload() const;

    // Perform atomic bitwise operations on the playload. External synchronization MUST be used if
    // threads are racing to modify and read the payload values.
    uint64_t PayloadFetchAnd(uint64_t arg);
    uint64_t PayloadFetchOr(uint64_t arg);

    // Add a reference, return true if the previous count is 0.
    bool Increment();

    // Tries to add a reference. Returns false if the ref count is already at 0. This is used when
    // operating on a raw pointer to a RefCounted instead of a valid Ref that may be soon deleted.
    bool TryIncrement();

    // Remove a reference. Returns true if this was the last reference.
    bool Decrement();

  private:
    std::atomic<uint64_t> mRefCount;
};

class RefCounted {
  public:
    static constexpr bool HasExternalRefCount = false;

    explicit RefCounted(uint64_t payload = 0);

    uint64_t GetRefCountForTesting() const;
    uint64_t GetRefCountPayload() const;
    uint64_t RefCountPayloadFetchAnd(uint64_t arg);
    uint64_t RefCountPayloadFetchOr(uint64_t arg);

    void AddRef();
    // Release() is called by internal code, so it's assumed that there is already a thread
    // synchronization in place for destruction.
    void Release();

    // Tries to add a reference. Returns false if the ref count is already at 0. This is used when
    // operating on a raw pointer to a RefCounted instead of a valid Ref that may be soon deleted.
    bool TryAddRef();

    void APIAddRef() { AddRef(); }
    void APIRelease() { Release(); }

  protected:
    virtual ~RefCounted();

    void ReleaseAndLockBeforeDestroy();

    // A Derived class may override these if they require a custom deleter.
    virtual void DeleteThis();
    // This calls DeleteThis() by default.
    virtual void LockAndDeleteThis();

    RefCount mRefCount;
};

}  // namespace dawn

#endif  // SRC_DAWN_COMMON_REFCOUNTED_H_