如何让另一个异步调用等待？

Question

如果其中一个异步调用捕获到在继续其他调用之前需要先完成的条件，如何暂停另一个异步调用？从下面的代码（简化）来看，当 makeRequest 得到 401 时，它应该调用 refreshSession 并暂停其他调用，直到这个完成。

let refreshSessionDispatchQueue = DispatchQueue(label: "refreshSession")
var refreshSessionJobQueue: [APIRequest] = []

// This function will be called by each of APIs that got 401 error code
private func refreshSession(errorCode: String? = nil, request: APIRequest) {
    refreshSessionDispatchQueue.async {
        self.refreshSessionJobQueue.append(request)
    }

    // The idea is, after all job appended to the jobQueue, let says after 1', it will call another function to execute another job
    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 1) {
        self.executeRefreshSessionJobQueue()
    }
}

// This is to execute refreshSession, and if it's succeed, all job on the jobQueue will be re-executed
private func executeRefreshSessionJobQueue() {
    DispatchQueue.main.async {
        let readyToRefreshSessionJobQueue = self.refreshSessionJobQueue
        
        if self.refreshSessionJobQueue.count > 0 {
            self.refreshSessionJobQueue = []

            self.refreshSession { [weak self] succeed in
                if succeed {
                    for job in readyToRefreshSessionJobQueue {
                        self?.makeRequest(baseURL: job.baseURL, endpoint: job.endpoint, method: job.method, encoding: job.encoding, headers: job.headers, params: job.params, customBody: job.customBody, completion: job.completion)
                    }
                    self?.refreshSessionJobQueue = []
                } else {
                    // And if it's failed, all the job should be removed and redirect the page to the login page
                    self?.refreshSessionJobQueue = []
                    ErrorHandler.relogin()
                }
            }
            
        }
    }
}

Answer 1

如果你在得到401时需要重试API，你可以尝试使用Alamofire的RequestInterceptor中的RequestRetrier。它基本上会重试遇到错误的请求，例如您的情况下的 401。

可以找到完整的实施示例 here。希望对你有帮助，干杯！

如何让另一个异步调用等待？

How to make another async call wait?

swift

queue

grand-central-dispatch

dispatch-queue