Reauthentication is required upon reconnection. The following example shows the process of configuring callback to an ARA client on line 7. Line 7 will always be used for ARA callback, whether the incoming call enters line 4, 7, or 8. Download this chapter. Configuring Asynchronous Callback. Router config-if ppp callback initiate.
Defines a chat script to be applied when a PPP client requests callback. Specifies a per-username callback dial string. Specifies a per-username rotary group for callback. Specifies a per-username line or set of lines for callback.
Router config-line autoselect ppp. Configures automatic PPP startup on a line or set of lines. Applies a chat script to a line or set of lines. Router config service exec-callback. Defines a chat script to be applied when clients dial in to the EXEC prompt. Does not require authentication on EXEC callback. Applies a chat script to the line or a set of lines. Want I need to achieve is upon receiving a silent push, I need to send an ajax request to the server, get back the data and save it persist it with CoreData.
Of course all this happens without the user ever opening the app. When he do opens up the app, a fresh data will be waiting. This is the silent push call back:.
Now, the problem is that when a notification arrives and the delegate is called, the ajax code executes, make the call to the server , and then exits. The code inside the ajax callback will not run. But, when I open the app and brings it to the foreground, suddenly this code section wakes up and continues to run.
This is not the desirable behaviour because when I open the app I still need to wait seconds for the those operations to run updating the UI etc. NewData into the ajax callback, but still this dose not fix the original problem, which is that this ajax callback code block won't execute. Trying to put some code together. Calling this completion handler is like telling the iOS you're done with your task and it can now put your app back to sleep or to the background.
You're calling it immediately. The block to execute when the download operation is complete. When calling this block, pass in the fetch result value that best describes the results of your download operation. You must call this handler and should do so as soon as possible. And also this answer could be helpful. To add to this answer. When I do this, I have gotten spotty support when starting that background fetch after didReceiveRemoteNotification.
I can start an Alamofire connection, but it may not work, it will die almost immediately. But this semaphore approach to block the main thread so you can make an asynchronous method behave like a synchronous one is an inadvisable approach, anyway.
You should actually embrace the asynchronous patterns and employ the completion block techniques in your own code. That link, How do I wait for an asynchronously dispatched block to finish? Sadly, this technique is misused with alarming frequency.
Specifically, in this case, the semaphore is not the appropriate pattern in your scenario because the semaphore pattern will block the main thread, something that we should never do within an app. By way of background, the semaphore technique is fine in the scenario discussed in that other thread, because it's a very different technical problem. It is being use in a special situation of a testing framework, not an app, and in a situation where a the test, itself, must happen on the main thread; b for the testing framework to function, it must block the main thread until the asynchronous task completes.
Furthermore, it also happens to work in that testing scenario, because the completion block does not take place on the main queue, avoiding the deadlock issue you're experiencing. None of these three conditions hold in your case. To use the semaphore technique in your situation is inadvisable. So, let's step back and look at your problem. I'm assuming that you have some method that looks like:. Even if you didn't have your deadlock problem, this is still the wrong pattern.
The first thing to notice here is that downloadContentsOfUrl now takes two callback arguments, one to be executed once the url has been retrieved, and the second one to be executed once the image has been downloaded. This will require passing that uiUpdatingCallback through two functions, just so the second one can utilise it, which violates the Law of Demeter.
Here we are defining our uiUpdatingCallback in the view controller. This will be executed at the end of the process by the imageDownloadCallback which we define next.
The imageDownloadCallback will be executed when the JsonDownloader has finished downloading the json data containing the image url asynchronously. We then pass two callbacks to the downloadContentsOfUrl function call and this uses the first callback within it, but passes the second callback the ui updating one through to be used later once the image has been downloaded asynchronusly. Can you see how this is starting to become a bit of a nightmare? We just want to be able to define what will happen next in the correct place, synchronously , without having to pass callbacks within callbacks.
Let's take a look at the entry point first, our ViewController. There are other things we need to do to make this work involving promises, but for now, this is the top level code. We've placed the image downloader callable into a class, but that's not the main change here.
Secondly, we have await , which will wait for the promise within it to resolve asynchronously. These can be two, separate, asynchronous-using structs and as long as we use promises, they will wait.
No callbacks, no passing functions around. This means that an asynchronous piece of code can return a value, via it's Promise, and the await call handles the waiting for that value to be returned.
We're writing code that looks synchronous! You may be a little confused about why we don't just do the following directly in the view controller itself:. Looks great, right? But what if you have the background threading within the JsonDownloader class instead, as many other classes do, both core and third-party, and not within your view controller?
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