在Swift 3.0中跟踪一批HTTP请求的解决方案 [英] A solution to track a batch of HTTP requests in swift 3.0

问题描述

我正在使用在iOS 10.0下运行的swift 3.0，我想制作一些在满足批处理条件时将触发的代码.

I am using swift 3.0 running under iOS 10.0 and I want to craft some code that fires when a batch condition is met.

for i in 0 ..< rex {
   async code, disappears and does it stuff
}

想象一下，异步代码是URL请求的集合，当我循环遍历它们时，它们基本上是后台的.现在，当"rex"请求完成后，我该如何触发更多代码?

Imagine the async code is a collection of URL requests, that basically background as soon as I loop thru them. Now how can I fire off more code when "rex" requests have completed?

我想设置一个计时器来监视和检查每一秒，但这肯定不是一个好的解决方案.

I thought of setting up a timer to watch and check every second, but its surely not a good solution.

我以为可以启动另一个线程来简单地监视正在收集的数据，并在其配额已满时触发，但这确实比计时器更糟糕.

I thought kicking off another thread to simply watch the data being collected, and fire when its quota is full, but well that's worse then the timer really.

我正在考虑在每个URL请求的末尾包含一个测试，以查看它是否是最后一个完成并使用NotificationCenter的示例，但这是最佳解决方案吗?

I am thinking to include a test at the end of each URL request to see if it was the last that completed and than uses the NotificationCenter, but is this the optimal solution?

推荐答案

虽然OperationQueue(又名NSOperationQueue)在很多情况下都是不错的选择，但它并不适合您的用例.问题在于URL请求被异步调用.您的NSOperation将在您从网络服务获得响应之前完成.

While OperationQueue (aka NSOperationQueue) is a good choice in many cases, it's not suitable for your use case. The problem is that URL requests are called asynchronously. Your NSOperation will finish before you get a response from the webservice.

改为使用DispatchGroup

let group = DispatchGroup()

// We need to dispatch to a background queue because we have 
// to wait for the response from the webservice
DispatchQueue.global(qos: .utility).async {
    for i in 0 ..< rex {
        group.enter()          // signal that you are starting a new task
        URLSession.shared.dataTask(with: urls[i]) { data, response, error in
            // handle your response
            // ....
            group.leave()      // signal that you are done with the task
        }.resume()
    }

    group.wait()               // don't ever call wait() on the main queue

    // Now all requests are complete
}

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