Alamofire和并发操作队列 [英] Alamofire and Concurrent Operation Queues

问题描述

我在并发操作队列中使用 Alamofire （AF）在我的项目中运行网络命令。有时候，AF的完成处理程序不会触发，而使我的NSOperation挂起（等待它永远不会收到的结束消息）。

I'm using Alamofire (AF) in a concurrent operation queue to run network commands in my project. Sometimes AF's completionHandler doesn't fire, leaving my NSOperation hanging (waiting for a finish message that it will never receive).

例如。我将看到响应日志，但下面的AF的dispatch_async没有相应的看到我日志：

Eg. I'll see the "response" log, but no corresponding "see me" log from AF's dispatch_async below:

public func response(priority: Int = DISPATCH_QUEUE_PRIORITY_DEFAULT, queue: dispatch_queue_t? = nil, serializer: (NSURLRequest, NSHTTPURLResponse?, NSData?, NSError?) -> (AnyObject?, NSError?), completionHandler: (NSURLRequest, NSHTTPURLResponse?, AnyObject?, NSError?) -> Void) -> Self {
NSLog("markse-response")

    dispatch_async(self.delegate.queue, {
NSLog("markse-see me")
        dispatch_async(dispatch_get_global_queue(priority, 0), {
            if var error = self.delegate.error {
                dispatch_async(queue ?? dispatch_get_main_queue(), {
                    completionHandler(self.request, self.response, nil, error)
                })
            } else {
                let (responseObject: AnyObject?, serializationError: NSError?) = serializer(self.request, self.response, self.delegate.data, nil)

                dispatch_async(queue ?? dispatch_get_main_queue(), {
                    completionHandler(self.request, self.response, responseObject, serializationError)
                })
            }
        })
    })

    return self
}

这是我的NSOperation（AsynchronousCommand是NSOperation的子类）：

This is my NSOperation (AsynchronousCommand is an NSOperation subclass):

import Alamofire

class SettingsListCommand: AsynchronousCommand {

    override func execute() {
        if cancelled { return }

        let endpoint = "https://api.github.com/users/cog404/orgs"

        DLogVerbose("AF request")
        weak var weakSelf = self
        Alamofire.request(.GET,
            endpoint,
            parameters:nil)
            .responseJSON {(request, response, JSON, error) in
                DLogVerbose("AF response")
                if let strongSelf = weakSelf {
                    if strongSelf.cancelled {
                        strongSelf.finish()
                        return
                    }
                    DLogVerbose(JSON)
                    strongSelf.finish()
                }
        }
    }

}

这仅偶尔发生，这使得调试非常困难。

This only happens 'occasionally', making this very difficult to debug.

对线程有深入了解的人知道会出什么问题吗？

Does anyone with a good understanding of threading know what could be going wrong?

任何建议非常感谢。 此处。

Any advice very much appreciated. A project to help illustrate the problem is here.

推荐答案

请求委托的分派队列是串行的，这意味着它仅一次处理一个块，以分派块（FIFO）的顺序。如果第二条日志语句未触发，则是因为前一个语句块尚未完成。

The request delegate's dispatch queue is serial, meaning that it will only process a single block at a time, in order of when the blocks were dispatched (FIFO). If the second log statement isn't firing, it's because the previous block didn't yet finish.

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