我们如何在swift中使用协议实现并发线程? [关闭]
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【中文标题】我们如何在swift中使用协议实现并发线程? [关闭]【英文标题】:How can we implement concurrency thread using protocol in swift? [closed] 【发布时间】:2017-08-11 05:25:31 【问题描述】:我在 ios 开发者职位的面试中被问到这个问题。
// Please design a read-write task queue where you can tag the reader task with label,
// where the the task with the same label should be executed sequentially, and the
// tasks with different labels could be executed concurrently. However, the writer
// would get the exclusive access where no concurrent task would happen at the
// same time with the writer task
// For example:
protocol ConcurrentQueueWithSerialization
// Submits a labeled task.
// All tasks with the same label will be serialized.
// Tasks with different labels will run concurrently.
// Use this method to submit a "read" operation from a particular reader.
func async(with label: String, task: @escaping () -> Void)
// Submits a task that will run concurrently with all other tasks regardless of their labels.
func async(task: @escaping () -> Void)
// Submits a labeled and delayed task.
func asyncAfter(deadline: DispatchTime, with label: String, task: @escaping () -> Void)
// Submits an unlabeled and delayed task.
func asyncAfter(deadline: DispatchTime, task: @escaping () -> Void)
// Submits a barrier task. Only one barrier task is allowed to run at a time.
// Works as a critical section for the queue.
// Use this method to submit a writer task.
func asyncBarrier(task: @escaping () -> Void)
class MyDispatchQueue: ConcurrentQueueWithSerialization
//TODO: write your implementation
面试官要求我在 MyDispatchQueue 类中实现上述协议。我试过但找不到解决方案。请帮我。提前致谢。
【问题讨论】:
SO 不是代码编写服务。你试过什么?你遇到了什么问题? 您的问题仅包含要求 - 它并未显示您为自己解决此问题所做的任何努力。请在此问题中添加您的尝试 - 因为该站点不是免费的“我们为您提供(家庭)工作”服务。除此之外:请转至help center 了解如何/在这里问什么。谢谢! 【参考方案1】:之前我建议使用目标队列,但更好的是,创建一个主并发队列,然后为命名队列创建串行队列,然后通过该主并发队列调度所有内容。与目标队列方法不同,这将尊重分派到命名队列的任务调度与分派到未命名队列的任务。
使用该实现,这是一个示例(Instruments“兴趣点”配置文件),其中我为名为“fred”和“ginger”的队列添加了任务,还添加了一个添加到未命名队列的任务,然后我添加了一个屏障任务,然后在上述每个队列中再添加两个任务。
如您所见,它尊重命名队列的串行性质,未命名队列是并发的,并且所有这些队列相对于彼此是并发的,但屏障是所有队列之间的屏障。
class MyDispatchQueue: ConcurrentQueueWithSerialization
private var namedQueues = [String: DispatchQueue]()
private var queue = DispatchQueue(label: Bundle.main.bundleIdentifier! + ".target", attributes: .concurrent)
private let lock = NSLock()
private func queue(with label: String) -> DispatchQueue
lock.lock()
defer lock.unlock()
if let queue = namedQueues[label] return queue
let queue = DispatchQueue(label: Bundle.main.bundleIdentifier! + "." + label)
namedQueues[label] = queue
return queue
func async(with label: String, task: @escaping () -> Void)
queue.async
self.queue(with: label).sync(execute: task)
func async(task: @escaping () -> Void)
queue.async(execute: task)
func asyncAfter(deadline: DispatchTime, with label: String, task: @escaping () -> Void)
queue.asyncAfter(deadline: deadline)
self.queue(with: label).sync(execute: task)
func asyncAfter(deadline: DispatchTime, task: @escaping () -> Void)
queue.asyncAfter(deadline: deadline, execute: task)
func asyncBarrier(task: @escaping () -> Void)
queue.async(flags: .barrier, execute: task)
注意,我还同步访问namedQueues
数组,以保证这个类的线程安全。
【讨论】:
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