ReleaseCallbackId 是 SurfaceFlinger 在显示之后设置的，通过 onTransactionCompleted() 传递给 client。Client 通过该对象查找回调函数执行 release 操作。

class ReleaseCallbackId : public Parcelable {
public:
    static const ReleaseCallbackId INVALID_ID;

    uint64_t bufferId;
    uint64_t framenumber;
    ReleaseCallbackId() {}
    ReleaseCallbackId(uint64_t bufferId, uint64_t framenumber)
          : bufferId(bufferId), framenumber(framenumber) {}
    status_t writeToParcel(Parcel* output) const override;
    status_t readFromParcel(const Parcel* input) override;

    bool operator==(const ReleaseCallbackId& rhs) const {
        return bufferId == rhs.bufferId && framenumber == rhs.framenumber;
    }
    bool operator!=(const ReleaseCallbackId& rhs) const { return !operator==(rhs); }
    std::string to_string() const {
        if (*this == INVALID_ID) return "INVALID_ID";

        return "bufferId:" + std::to_string(bufferId) +
                " framenumber:" + std::to_string(framenumber);
    }
};