我已经搜索了Swift的书籍,但找不到@synchronized的Swift版本。我如何做互斥在Swift?
当前回答
类似于Objective-C中的@synchronized指令,在Swift中可以有任意的返回类型和漂亮的重抛出行为。
// Swift 3
func synchronized<T>(_ lock: AnyObject, _ body: () throws -> T) rethrows -> T {
objc_sync_enter(lock)
defer { objc_sync_exit(lock) }
return try body()
}
使用defer语句可以直接返回一个值,而不需要引入临时变量。
在Swift 2中,为闭包添加@noescape属性可以进行更多的优化:
// Swift 2
func synchronized<T>(lock: AnyObject, @noescape _ body: () throws -> T) rethrows -> T {
objc_sync_enter(lock)
defer { objc_sync_exit(lock) }
return try body()
}
基于GNewc[1](我喜欢任意返回类型)和Tod Cunningham[2](我喜欢延迟)的答案。
其他回答
你可以使用GCD。它比@synchronized更详细一点,但可以作为替代品:
let serialQueue = DispatchQueue(label: "com.test.mySerialQueue")
serialQueue.sync {
// code
}
使用Swift的属性包装器,这是我现在使用的:
@propertyWrapper public struct NCCSerialized<Wrapped> {
private let queue = DispatchQueue(label: "com.nuclearcyborg.NCCSerialized_\(UUID().uuidString)")
private var _wrappedValue: Wrapped
public var wrappedValue: Wrapped {
get { queue.sync { _wrappedValue } }
set { queue.sync { _wrappedValue = newValue } }
}
public init(wrappedValue: Wrapped) {
self._wrappedValue = wrappedValue
}
}
然后你可以这样做:
@NCCSerialized var foo: Int = 10
or
@NCCSerialized var myData: [SomeStruct] = []
然后像往常一样访问变量。
细节
Xcode 8.3.1, Swift 3.1
Task
从不同的线程读写值(异步)。
Code
class AsyncObject<T>:CustomStringConvertible {
private var _value: T
public private(set) var dispatchQueueName: String
let dispatchQueue: DispatchQueue
init (value: T, dispatchQueueName: String) {
_value = value
self.dispatchQueueName = dispatchQueueName
dispatchQueue = DispatchQueue(label: dispatchQueueName)
}
func setValue(with closure: @escaping (_ currentValue: T)->(T) ) {
dispatchQueue.sync { [weak self] in
if let _self = self {
_self._value = closure(_self._value)
}
}
}
func getValue(with closure: @escaping (_ currentValue: T)->() ) {
dispatchQueue.sync { [weak self] in
if let _self = self {
closure(_self._value)
}
}
}
var value: T {
get {
return dispatchQueue.sync { _value }
}
set (newValue) {
dispatchQueue.sync { _value = newValue }
}
}
var description: String {
return "\(_value)"
}
}
使用
print("Single read/write action")
// Use it when when you need to make single action
let obj = AsyncObject<Int>(value: 0, dispatchQueueName: "Dispatch0")
obj.value = 100
let x = obj.value
print(x)
print("Write action in block")
// Use it when when you need to make many action
obj.setValue{ (current) -> (Int) in
let newValue = current*2
print("previous: \(current), new: \(newValue)")
return newValue
}
完整的样品
扩展DispatchGroup
extension DispatchGroup {
class func loop(repeatNumber: Int, action: @escaping (_ index: Int)->(), completion: @escaping ()->()) {
let group = DispatchGroup()
for index in 0...repeatNumber {
group.enter()
DispatchQueue.global(qos: .utility).async {
action(index)
group.leave()
}
}
group.notify(queue: DispatchQueue.global(qos: .userInitiated)) {
completion()
}
}
}
类ViewController
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
//sample1()
sample2()
}
func sample1() {
print("=================================================\nsample with variable")
let obj = AsyncObject<Int>(value: 0, dispatchQueueName: "Dispatch1")
DispatchGroup.loop(repeatNumber: 5, action: { index in
obj.value = index
}) {
print("\(obj.value)")
}
}
func sample2() {
print("\n=================================================\nsample with array")
let arr = AsyncObject<[Int]>(value: [], dispatchQueueName: "Dispatch2")
DispatchGroup.loop(repeatNumber: 15, action: { index in
arr.setValue{ (current) -> ([Int]) in
var array = current
array.append(index*index)
print("index: \(index), value \(array[array.count-1])")
return array
}
}) {
print("\(arr.value)")
}
}
}
试题:NSRecursiveLock
一种锁,可以被同一线程多次获得 导致死锁。
let lock = NSRecursiveLock()
func f() {
lock.lock()
//Your Code
lock.unlock()
}
func f2() {
lock.lock()
defer {
lock.unlock()
}
//Your Code
}
Objective-C同步特性支持递归和 可重入代码。线程可以多次使用同一个信号量 递归的方式;其他线程被阻止使用它,直到 线程释放使用它获得的所有锁;也就是说,每一个 @synchronized()块正常退出或通过异常退出。 源
是什么
final class SpinLock {
private let lock = NSRecursiveLock()
func sync<T>(action: () -> T) -> T {
lock.lock()
defer { lock.unlock() }
return action()
}
}
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