原文地址
什么是线程安全
当一段代码被多个线程执行，执行后的结果和多个线程依次执行后的结果一致，那么这段代码就是线程安全的。
产生线程不安全原因
- 线程是抢占执行的。
- 有的操作不是原子的。当 cpu 执行一个线程过程时，调度器可能调走CPU，去执行另一个线程，此线程的操作可能还没有结束；（通过锁来解决）
- 多个线程尝试修改同一个变量
- 内存可变性
为什么要线程安全
线程安全是程序能够正确执行并得到预期结果的保证
数组怎么实现线程安全
- NSLock 等互斥锁
- GCD barrier
- 读写锁(pthread_rwlock_t)
pthread_rwlock_t 实现数组安全
import Foundation
// MARK: - ThreadSafeArray
public class ThreadSafeArray {
private var array: [Element] = []
private var lock = pthread_rwlock_t()
public init() {
let status = pthread_rwlock_init(&lock, nil)
assert(status == 0)
}
public convenience init(array: [Element]) {
self.init()
self.array = array
}
deinit {
pthread_rwlock_destroy(&lock)
}
}
// MARK: - Properties
public extension ThreadSafeArray {
var first: Element? {
var result: Element?
pthread_rwlock_rdlock(&lock)
result = array.first
pthread_rwlock_unlock(&lock)
return result
}
var last: Element? {
var result: Element?
pthread_rwlock_rdlock(&lock)
result = array.last
pthread_rwlock_unlock(&lock)
return result
}
var count: Int {
pthread_rwlock_rdlock(&lock)
let count = array.count
pthread_rwlock_unlock(&lock)
return count
}
var isEmpty: Bool {
pthread_rwlock_rdlock(&lock)
let result = (array.count > 0)
pthread_rwlock_unlock(&lock)
return result
}
var description: String {
pthread_rwlock_rdlock(&lock)
let str = array.description
pthread_rwlock_unlock(&lock)
return str
}
}
// MARK: - Immutable
public extension ThreadSafeArray {
func first(where predicate: (Element)->Bool)->Element? {
pthread_rwlock_rdlock(&lock)
let result = array.first(where: predicate)
pthread_rwlock_unlock(&lock)
return result
}
func last(where predicate: (Element)->Bool)->Element? {
pthread_rwlock_rdlock(&lock)
let result = array.last(where: predicate)
pthread_rwlock_unlock(&lock)
return result
}
func filter(isIncluded: @escaping (Element)->Bool) ->ThreadSafeArray {
pthread_rwlock_rdlock(&lock)
let result = array.filter(isIncluded)
pthread_rwlock_unlock(&lock)
return ThreadSafeArray(array: result)
}
func index(where predicate: (Element)->Bool)-> Int? {
pthread_rwlock_rdlock(&lock)
let result = array.firstIndex(where: predicate)
pthread_rwlock_unlock(&lock)
return result
}
func sorted(by areInIncreasingOrder: (Element, Element)->Bool)->ThreadSafeArray {
pthread_rwlock_rdlock(&lock)
let result = array.sorted(by: areInIncreasingOrder)
let newArray = ThreadSafeArray(array: result)
pthread_rwlock_unlock(&lock)
return newArray
}
func map(_ transform: @escaping (Element)->T) ->[T] {
pthread_rwlock_rdlock(&lock)
let result = array.map(transform)
pthread_rwlock_unlock(&lock)
return result
}
func compactMap(_ transform: (Element)->T)->[T] {
pthread_rwlock_rdlock(&lock)
let result = array.compactMap(transform)
pthread_rwlock_unlock(&lock)
return result
}
func reduce(initialResult: T, _ nexPartialResult: @escaping (T, Element)->T)->T {
pthread_rwlock_rdlock(&lock)
let result = array.reduce(initialResult, nexPartialResult)
pthread_rwlock_unlock(&lock)
return result
}
func forEach(_ body: (Element)->Void) {
pthread_rwlock_rdlock(&lock)
array.forEach(body)
pthread_rwlock_unlock(&lock)
}
func contains(where predicate: (Element)->Bool)->Bool {
pthread_rwlock_rdlock(&lock)
let result = array.contains(where: predicate)
pthread_rwlock_unlock(&lock)
return result
}
func allSatisfy(_ predicate: (Element)->Bool)->Bool {
pthread_rwlock_rdlock(&lock)
let result = array.allSatisfy(predicate)
pthread_rwlock_unlock(&lock)
return result
}
}
// MARK: - Mutable
public extension ThreadSafeArray {
func append(_ element: Element) {
pthread_rwlock_wrlock(&lock)
array.append(element)
pthread_rwlock_unlock(&lock)
}
func append(_ elements: [Element]) {
pthread_rwlock_wrlock(&lock)
array += elements
pthread_rwlock_unlock(&lock)
}
func insert(_ element: Element, at index: Int) {
pthread_rwlock_wrlock(&lock)
array.insert(element, at: index)
pthread_rwlock_unlock(&lock)
}
func remove(at index: Int, completion: ((Element)->Void)? = nil) {
pthread_rwlock_wrlock(&lock)
if index > 0, index < count {
let e = array.remove(at: index)
completion?(e)
}
pthread_rwlock_unlock(&lock)
}
func remove(where predicate: @escaping (Element)->Bool, completion: (([Element])->Void)? = nil) {
pthread_rwlock_wrlock(&lock)
var elements = [Element]()
while let index = array.firstIndex(where: predicate) {
elements.append(array.remove(at: index))
}
completion?(elements)
pthread_rwlock_unlock(&lock)
}
func removeAll(completion: (([Element])->Void)? = nil) {
pthread_rwlock_wrlock(&lock)
let elements = array
array.removeAll()
completion?(elements)
pthread_rwlock_unlock(&lock)
}
}
public extension ThreadSafeArray {
subscript(index: Int)->Element? {
get {
pthread_rwlock_rdlock(&lock)
var result: Element?
guard self.array.startIndex..Bool {
pthread_rwlock_rdlock(&lock)
let result = self.array.contains(element)
pthread_rwlock_unlock(&lock)
return result
}
}
// MARK: - Infix operators
public extension ThreadSafeArray {
/// Adds a new element at the end of the array.
///
/// - Parameters:
/// - left: The collection to append to.
/// - right: The element to append to the array.
static func +=(left: inout ThreadSafeArray, right: Element) {
left.append(right)
}
/// Adds new elements at the end of the array.
///
/// - Parameters:
/// - left: The collection to append to.
/// - right: The elements to append to the array.
static func +=(left: inout ThreadSafeArray, right: [Element]) {
left.append(right)
}
}
参考
iOS多线程到底哪里不安全
读写锁
Swift线程安全详解－概念，三种锁，死锁，Atomic，synchronized