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//关联`debounceAsyncAfter` 的调用的键。
struct DebounceKey: Equatable, Hashable {
        fileprivate let lockedState = UnfairLockedState<UInt64>(0)
        init() {}
        
        static func == (lhs: DebounceKey, rhs: DebounceKey) -> Bool {
            return lhs.lockedState === rhs.lockedState
        }
        
        func hash(into hasher: inout Hasher) {
            hasher.combine(ObjectIdentifier(lockedState))
        }
}

//限定时间内只发生一个去抖动的异步块
func debounceAsyncAfter(deadline: DispatchTime, key: DebounceKey, qos: DispatchQoS = .unspecified, flags: DispatchWorkItemFlags = [], execute work: @escaping () -> Void) {
        let epoch = key.lockedState.sync { (x) -> UInt64 in
            x += 1
            return x
        }
        asyncAfter(deadline: deadline, qos: qos, flags: flags) {
            guard epoch == key.lockedState.sync({ $0 }) else { return }
            work()
        }
}

//限定时间内只发生去抖动的一组异步块
func debounceAsyncAfter(wallDeadline: DispatchWallTime, key: DebounceKey, qos: DispatchQoS = .unspecified, flags: DispatchWorkItemFlags = [], execute work: @escaping () -> Void) {
        let epoch = key.lockedState.sync { (x) -> UInt64 in
            x += 1
            return x
        }
        asyncAfter(wallDeadline: wallDeadline, qos: qos, flags: flags) {
            guard epoch == key.lockedState.sync({ $0 }) else { return }
            work()
        }
}