ios - 使用 NSURLSession 发出同步请求

Question

我在另一个线程中调用了一些函数:

dispatch_async(dispatch_get_global_queue(priority, 0)) {
     self.someFunction()
}

然后在这个函数中我想做同步请求:

let config = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: config)
let dataSemaphore = dispatch_semaphore_create(0)

let task = session.dataTaskWithRequest(urlRequest, completionHandler: { (data, response, error) in
guard let responseData = data else {
    print("Error: did not receive data")
    return
}
guard error == nil else {
    print("error calling GET")
    print(error)
    return
    }
    print("ASYNC")
})
task.resume()

dispatch_semaphore_wait(dataSemaphore, DISPATCH_TIME_FOREVER)

print("SYNC")

但是线程在这一行停止dispatch_semaphore_wait(dataSemaphore, DISPATCH_TIME_FOREVER)

Answer 1

你从来没有发出信号量，把它放在你的完成处理程序的末尾:

dispatch_semaphore_signal(dataSemaphore)