我希望能够原子地增加一个计数器，我找不到任何关于如何做的参考。
根据评论添加更多信息：
我想做这样的事情：
class Counter {
private var mux Mutex
private (set) value Int
func increment (){
mux.lock()
value += 1
mux.unlock()
}
}
答案 0 :(得分：57)
有一长串OSAtomicIncrement和OSAtomicDecrement 允许您递增和递减整数值的函数 以原子方式 - 线程安全，无需锁定（或使用 队列）。如果您需要增加全局计数器，这些可能很有用 从多个线程进行统计。如果你所做的只是增加一个 全局计数器，无障碍OSAtomicIncrement版本很好， 当没有争用时，他们打电话便宜。
这些函数适用于固定大小的整数，您可以选择 32位或64位变体，具体取决于您的需求：
class Counter {
private (set) var value : Int32 = 0
func increment () {
OSAtomicIncrement32(&value)
}
}
（注意：正如Erik Aigner正确注意到的那样，OSAtomicIncrement32和
朋友们从macOS 10.12 / iOS 10.10开始被弃用。 Xcode 8建议使用<stdatomic.h>中的函数。然而，这似乎很难，
比较Swift 3: atomic_compare_exchange_strong和https://openradar.appspot.com/27161329。
因此，以下基于GCD的方法似乎是最好的
解决方案现在。）
或者，可以使用GCD队列进行同步。 来自“并发编程指南”中的Dispatch Queues：
...使用调度队列，您可以将两个任务都添加到序列中 调度队列以确保只有一个任务修改了资源 任何给定的时间。这种基于队列的同步更多 比锁更有效，因为锁总是需要昂贵的内核 陷入有争议和无争议的案件，而派遣 queue主要在应用程序的进程空间中工作 在绝对必要时调用内核。
在你的情况下
// Swift 2:
class Counter {
private var queue = dispatch_queue_create("your.queue.identifier", DISPATCH_QUEUE_SERIAL)
private (set) var value: Int = 0
func increment() {
dispatch_sync(queue) {
value += 1
}
}
}
// Swift 3:
class Counter {
private var queue = DispatchQueue(label: "your.queue.identifier")
private (set) var value: Int = 0
func increment() {
queue.sync {
value += 1
}
}
}
有关更复杂的示例，请参阅Adding items to Swift array across multiple threads causing issues (because arrays aren't thread safe) - how do I get around that?或GCD with static functions of a struct。这个帖子 What advantage(s) does dispatch_sync have over @synchronized?也非常有趣。
答案 1 :(得分：24)
在这种情况下，队列是一种矫枉过正。您可以为此目的使用 Swift 3 中引入的DispatchSemaphore，如下所示：
import Foundation
public class AtomicInteger {
private let lock = DispatchSemaphore(value: 1)
private var value = 0
// You need to lock on the value when reading it too since
// there are no volatile variables in Swift as of today.
public func get() -> Int {
lock.wait()
defer { lock.signal() }
return value
}
public func set(_ newValue: Int) {
lock.wait()
defer { lock.signal() }
value = newValue
}
public func incrementAndGet() -> Int {
lock.wait()
defer { lock.signal() }
value += 1
return value
}
}
该课程的最新版本可用over here。
答案 2 :(得分：10)
我知道这个问题已经有点老了，但我最近偶然发现了同样的问题。 经过一番研究和阅读http://www.cocoawithlove.com/blog/2016/06/02/threads-and-mutexes.html这样的帖子后，我想出了一个原子计数器的解决方案。也许它也会帮助别人。
import Foundation
class AtomicCounter {
private var mutex = pthread_mutex_t()
private var counter: UInt = 0
init() {
pthread_mutex_init(&mutex, nil)
}
deinit {
pthread_mutex_destroy(&mutex)
}
func incrementAndGet() -> UInt {
pthread_mutex_lock(&mutex)
defer {
pthread_mutex_unlock(&mutex)
}
counter += 1
return counter
}
}
答案 3 :(得分：7)
import Foundation
struct AtomicInteger<Type>: BinaryInteger where Type: BinaryInteger {
typealias Magnitude = Type.Magnitude
typealias IntegerLiteralType = Type.IntegerLiteralType
typealias Words = Type.Words
fileprivate var value: Type
private var semaphore = DispatchSemaphore(value: 1)
fileprivate func _wait() { semaphore.wait() }
fileprivate func _signal() { semaphore.signal() }
init() { value = Type() }
init(integerLiteral value: AtomicInteger.IntegerLiteralType) {
self.value = Type(integerLiteral: value)
}
init<T>(_ source: T) where T : BinaryInteger {
value = Type(source)
}
init(_ source: Int) {
value = Type(source)
}
init<T>(clamping source: T) where T : BinaryInteger {
value = Type(clamping: source)
}
init?<T>(exactly source: T) where T : BinaryInteger {
guard let value = Type(exactly: source) else { return nil }
self.value = value
}
init<T>(truncatingIfNeeded source: T) where T : BinaryInteger {
value = Type(truncatingIfNeeded: source)
}
init?<T>(exactly source: T) where T : BinaryFloatingPoint {
guard let value = Type(exactly: source) else { return nil }
self.value = value
}
init<T>(_ source: T) where T : BinaryFloatingPoint {
value = Type(source)
}
}
// Instance Properties
extension AtomicInteger {
var words: Type.Words {
_wait(); defer { _signal() }
return value.words
}
var bitWidth: Int {
_wait(); defer { _signal() }
return value.bitWidth
}
var trailingZeroBitCount: Int {
_wait(); defer { _signal() }
return value.trailingZeroBitCount
}
var magnitude: Type.Magnitude {
_wait(); defer { _signal() }
return value.magnitude
}
}
// Type Properties
extension AtomicInteger {
static var isSigned: Bool { return Type.isSigned }
}
// Instance Methods
extension AtomicInteger {
func quotientAndRemainder(dividingBy rhs: AtomicInteger<Type>) -> (quotient: AtomicInteger<Type>, remainder: AtomicInteger<Type>) {
_wait(); defer { _signal() }
rhs._wait(); defer { rhs._signal() }
let result = value.quotientAndRemainder(dividingBy: rhs.value)
return (AtomicInteger(result.quotient), AtomicInteger(result.remainder))
}
func signum() -> AtomicInteger<Type> {
_wait(); defer { _signal() }
return AtomicInteger(value.signum())
}
}
extension AtomicInteger {
fileprivate static func atomicAction<Result, Other>(lhs: AtomicInteger<Type>,
rhs: Other, closure: (Type, Type) -> (Result)) -> Result where Other : BinaryInteger {
lhs._wait(); defer { lhs._signal() }
var rhsValue = Type(rhs)
if let rhs = rhs as? AtomicInteger {
rhs._wait(); defer { rhs._signal() }
rhsValue = rhs.value
}
let result = closure(lhs.value, rhsValue)
return result
}
fileprivate static func atomicActionAndResultSaving<Other>(lhs: inout AtomicInteger<Type>,
rhs: Other, closure: (Type, Type) -> (Type)) where Other : BinaryInteger {
lhs._wait(); defer { lhs._signal() }
var rhsValue = Type(rhs)
if let rhs = rhs as? AtomicInteger {
rhs._wait(); defer { rhs._signal() }
rhsValue = rhs.value
}
let result = closure(lhs.value, rhsValue)
lhs.value = result
}
}
// Math Operator Functions
extension AtomicInteger {
static func != <Other>(lhs: AtomicInteger, rhs: Other) -> Bool where Other : BinaryInteger {
return atomicAction(lhs: lhs, rhs: rhs) { $0 != $1 }
}
static func != (lhs: AtomicInteger, rhs: AtomicInteger) -> Bool {
return atomicAction(lhs: lhs, rhs: rhs) { $0 != $1 }
}
static func % (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 % $1 }
return self.init(value)
}
static func %= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 % $1 }
}
static func & (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 & $1 }
return self.init(value)
}
static func &= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 & $1 }
}
static func * (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 * $1 }
return self.init(value)
}
static func *= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 * $1 }
}
static func + (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 + $1 }
return self.init(value)
}
static func += (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 + $1 }
}
static func - (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 - $1 }
return self.init(value)
}
static func -= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 - $1 }
}
static func / (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 / $1 }
return self.init(value)
}
static func /= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 / $1 }
}
}
// Shifting Operator Functions
extension AtomicInteger {
static func << <RHS>(lhs: AtomicInteger<Type>, rhs: RHS) -> AtomicInteger where RHS : BinaryInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 << $1 }
return self.init(value)
}
static func <<= <RHS>(lhs: inout AtomicInteger, rhs: RHS) where RHS : BinaryInteger {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 << $1 }
}
static func >> <RHS>(lhs: AtomicInteger, rhs: RHS) -> AtomicInteger where RHS : BinaryInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 >> $1 }
return self.init(value)
}
static func >>= <RHS>(lhs: inout AtomicInteger, rhs: RHS) where RHS : BinaryInteger {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 >> $1 }
}
}
// Comparing Operator Functions
extension AtomicInteger {
static func < <Other>(lhs: AtomicInteger<Type>, rhs: Other) -> Bool where Other : BinaryInteger {
return atomicAction(lhs: lhs, rhs: rhs) { $0 < $1 }
}
static func <= (lhs: AtomicInteger, rhs: AtomicInteger) -> Bool {
return atomicAction(lhs: lhs, rhs: rhs) { $0 <= $1 }
}
static func == <Other>(lhs: AtomicInteger, rhs: Other) -> Bool where Other : BinaryInteger {
return atomicAction(lhs: lhs, rhs: rhs) { $0 == $1 }
}
static func > <Other>(lhs: AtomicInteger, rhs: Other) -> Bool where Other : BinaryInteger {
return atomicAction(lhs: lhs, rhs: rhs) { $0 > $1 }
}
static func > (lhs: AtomicInteger, rhs: AtomicInteger) -> Bool {
return atomicAction(lhs: lhs, rhs: rhs) { $0 > $1 }
}
static func >= (lhs: AtomicInteger, rhs: AtomicInteger) -> Bool {
return atomicAction(lhs: lhs, rhs: rhs) { $0 >= $1 }
}
static func >= <Other>(lhs: AtomicInteger, rhs: Other) -> Bool where Other : BinaryInteger {
return atomicAction(lhs: lhs, rhs: rhs) { $0 >= $1 }
}
}
// Binary Math Operator Functions
extension AtomicInteger {
static func ^ (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 ^ $1 }
return self.init(value)
}
static func ^= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 ^ $1 }
}
static func | (lhs: AtomicInteger, rhs: AtomicInteger) -> AtomicInteger {
let value = atomicAction(lhs: lhs, rhs: rhs) { $0 | $1 }
return self.init(value)
}
static func |= (lhs: inout AtomicInteger, rhs: AtomicInteger) {
atomicActionAndResultSaving(lhs: &lhs, rhs: rhs) { $0 | $1 }
}
static prefix func ~ (x: AtomicInteger) -> AtomicInteger {
x._wait(); defer { x._signal() }
return self.init(x.value)
}
}
// Hashable
extension AtomicInteger {
var hashValue: Int {
_wait(); defer { _signal() }
return value.hashValue
}
func hash(into hasher: inout Hasher) {
_wait(); defer { _signal() }
value.hash(into: &hasher)
}
}
// Get/Set
extension AtomicInteger {
// Single actions
func get() -> Type {
_wait(); defer { _signal() }
return value
}
mutating func set(value: Type) {
_wait(); defer { _signal() }
self.value = value
}
// Multi-actions
func get(closure: (Type)->()) {
_wait(); defer { _signal() }
closure(value)
}
mutating func set(closure: (Type)->(Type)) {
_wait(); defer { _signal() }
self.value = closure(value)
}
}
// Usage Samples
let numA = AtomicInteger<Int8>(0)
let numB = AtomicInteger<Int16>(0)
let numC = AtomicInteger<Int32>(0)
let numD = AtomicInteger<Int64>(0)
var num1 = AtomicInteger<Int>(0)
num1 += 1
num1 -= 1
num1 = 10
num1 = num1/2
var num2 = 0
num2 = num1.get()
num1.set(value: num2*5)
// lock num1 to do several actions
num1.get { value in
//...
}
num1.set { value in
//...
return value
}
import Foundation
var x = AtomicInteger<Int>(0)
let dispatchGroup = DispatchGroup()
private func async(dispatch: DispatchQueue, closure: @escaping (DispatchQueue)->()) {
for _ in 0 ..< 100 {
dispatchGroup.enter()
dispatch.async {
print("Queue: \(dispatch.qos.qosClass)")
closure(dispatch)
dispatchGroup.leave()
}
}
}
func sample() {
let closure1: (DispatchQueue)->() = { _ in x += 1 }
let closure2: (DispatchQueue)->() = { _ in x -= 1 }
async(dispatch: .global(qos: .userInitiated), closure: closure1) // result: x += 100
async(dispatch: .global(qos: .utility), closure: closure1) // result: x += 100
async(dispatch: .global(qos: .background), closure: closure2) // result: x -= 100
async(dispatch: .global(qos: .default), closure: closure2) // result: x -= 100
}
sample()
dispatchGroup.wait()
print(x) // expected result x = 0
答案 4 :(得分：2)
我通过使用一些重载运算符改进了@florian的答案：
import Foundation
class AtomicInt {
private var mutex = pthread_mutex_t()
private var integer: Int = 0
var value : Int {
return integer
}
//MARK: - lifecycle
init(_ value: Int = 0) {
pthread_mutex_init(&mutex, nil)
integer = value
}
deinit {
pthread_mutex_destroy(&mutex)
}
//MARK: - Public API
func increment() {
pthread_mutex_lock(&mutex)
defer {
pthread_mutex_unlock(&mutex)
}
integer += 1
}
func incrementAndGet() -> Int {
pthread_mutex_lock(&mutex)
defer {
pthread_mutex_unlock(&mutex)
}
integer += 1
return integer
}
func decrement() {
pthread_mutex_lock(&mutex)
defer {
pthread_mutex_unlock(&mutex)
}
integer -= 1
}
func decrementAndGet() -> Int {
pthread_mutex_lock(&mutex)
defer {
pthread_mutex_unlock(&mutex)
}
integer -= 1
return integer
}
//MARK: - overloaded operators
static func > (lhs: AtomicInt, rhs: Int) -> Bool {
return lhs.integer > rhs
}
static func < (lhs: AtomicInt, rhs: Int) -> Bool {
return lhs.integer < rhs
}
static func == (lhs: AtomicInt, rhs: Int) -> Bool {
return lhs.integer == rhs
}
static func > (lhs: Int, rhs: AtomicInt) -> Bool {
return lhs > rhs.integer
}
static func < (lhs: Int, rhs: AtomicInt) -> Bool {
return lhs < rhs.integer
}
static func == (lhs: Int, rhs: AtomicInt) -> Bool {
return lhs == rhs.integer
}
func test() {
let atomicInt = AtomicInt(0)
atomicInt.increment()
atomicInt.decrement()
if atomicInt > 10 { print("bigger than 10") }
if atomicInt < 10 { print("smaller than 10") }
if atomicInt == 10 { print("its 10") }
if 10 > atomicInt { print("10 is bigger") }
if 10 < atomicInt { print("10 is smaller") }
if 10 == atomicInt { print("its 10") }
}
}
答案 5 :(得分：1)
您可以查看由 Apple 托管的支持通用类型的 Swift Atomics 库
答案 6 :(得分：0)
在撰写本文时，这被证明是最简单的解决方案，直到我们获得适当的Swift原子类型为止。您可以使用该通用类来设置任何种类的原子value。
为此滥用DispatchQueue是没有道理的。首先，您只能使用基于块的同步，创建可能不必要的闭包/堆栈框架，仅用于内部DispatchSemaphore队列，而不是直接创建队列。
final class Atomic<T> {
private let sema = DispatchSemaphore(value: 1)
private var _value: T
init (_ value: T) {
_value = value
}
var value: T {
get {
sema.wait()
defer {
sema.signal()
}
return _value
}
set {
sema.wait()
_value = newValue
sema.signal()
}
}
func swap(_ value: T) -> T {
sema.wait()
let v = _value
_value = value
sema.signal()
return v
}
}
用法：
let atomicBool = Atomic<Bool>(false)
atomicBool.value = true
let atomicInt = Atomic<Int>(0)
let oldInt = atomicInt.swap(1)
如果您想增加Int，请使用以下扩展名
extension Atomic where T == Int {
func increment(n: Int) -> Int {
sema.wait()
let v = _value + n
_value = v
sema.signal()
return v
}
}
答案 7 :(得分：0)