0.swift

// comparing atomic operation performance

import Foundation

final class Locking {

    static let shared = Locking()

    private(set) var isLocked: Bool = false
    private let _lock = NSLock()

    func lock() {
        _lock.lock(); defer { _lock.unlock(); }
        if isLocked { return }
        isLocked = true
    }

    func unlock() {
        _lock.lock(); defer { _lock.unlock(); }
        isLocked = false
    }
}

final class Atomic<A> {
    private let queue = DispatchQueue(label: "Atomic serial queue")
    private var _value: A
    init(_ value: A) {
        self._value = value
    }

    var value: A {
        get {
            return queue.sync { self._value }
        }
    }

    func mutate(_ transform: (inout A) -> ()) {
        queue.sync {
            transform(&self._value)
        }
    }
}

extension Date {
    var millisecondsSince1970:Int64 {
        return Int64((self.timeIntervalSince1970 * 1000.0).rounded())
    }

    init(milliseconds:Int64) {
        self = Date(timeIntervalSince1970: TimeInterval(milliseconds) / 1000)
    }
}

func measure(_ f: () -> ()) {
    let begin = Date().millisecondsSince1970
    f()
    let end = Date().millisecondsSince1970
    print(end - begin)
}

let l = Locking.shared
let a = Atomic(false)
//let uber = AtomicBool(initialValue: false)

let range = (0..<1000000)
measure {
    range.forEach { _ in l.lock(); l.unlock() }
}
measure {
    range.forEach { _ in a.mutate { $0 = true }; a.mutate { $0 = false } }
}
//measure {
//    range.forEach { _ in
//        uber.compareAndSet(expect: false, newValue: true)
//        uber.compareAndSet(expect: true, newValue: false)
//    }
//}
//measure {
//    range.forEach { _ in
//        _ = uber.getAndSet(newValue: true)
//        _ = uber.getAndSet(newValue: false)
//    }
//}