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
基于ɲeuroburɳ,测试一个子类用例
class Foo: NSObject {
func test() {
print("1")
objc_sync_enter(self)
defer {
objc_sync_exit(self)
print("3")
}
print("2")
}
}
class Foo2: Foo {
override func test() {
super.test()
print("11")
objc_sync_enter(self)
defer {
print("33")
objc_sync_exit(self)
}
print("22")
}
}
let test = Foo2()
test.test()
输出:
1
2
3
11
22
33
总之,这里给出了更常见的方法,包括返回值或void和throw
import Foundation
extension NSObject {
func synchronized<T>(lockObj: AnyObject!, closure: () throws -> T) rethrows -> T
{
objc_sync_enter(lockObj)
defer {
objc_sync_exit(lockObj)
}
return try closure()
}
}
Dispatch_barrier_async是更好的方法,同时不会阻塞当前线程。
dispatch_barrier_async (accessQueue, { 字典对象。ID = object })
在现代Swift 5中,具有返回功能:
/**
Makes sure no other thread reenters the closure before the one running has not returned
*/
@discardableResult
public func synchronized<T>(_ lock: AnyObject, closure:() -> T) -> T {
objc_sync_enter(lock)
defer { objc_sync_exit(lock) }
return closure()
}
像这样使用它,以利用返回值功能:
let returnedValue = synchronized(self) {
// Your code here
return yourCode()
}
或者像这样:
synchronized(self) {
// Your code here
yourCode()
}
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)")
}
}
}
推荐文章
- 我应该如何从字符串中删除所有的前导空格?- - - - - -斯威夫特
- 为什么这个Java程序会终止,尽管它显然不应该(也没有)终止?
- 同步vs锁定
- Swift:理解// MARK
- Swift -转换为绝对值
- Swift编译器错误:“框架模块内的非模块化头”
- 从父iOS访问容器视图控制器
- NSRange从Swift Range?
- 我可以使用范围操作符与if语句在Swift?
- LMAX的干扰模式是如何工作的?
- 在Swift中转换字符串为日期
- 点击按钮时如何打开手机设置?
- 在Swift中使用自定义消息抛出错误/异常的最简单方法?
- 编译器错误:带有Objective-C选择器的方法与前面带有相同Objective-C选择器的声明冲突
- 如何在Swift中获得唯一的设备ID ?