如何让另一个异步调用等待

Question

如果其中一个异步调用捕捉到需要在继续其他调用之前先完成的条件，如何暂停另一个异步呼叫？根据下面的代码(简化(，当makeRequest得到401时，它应该调用refreshSession并暂停其他调用，直到这个调用完成。

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

如果在获取401时需要重试API，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401。

实现的完整示例可以在这里找到。希望有帮助，加油！