how to keep dataTask communication in background mode

See my response here.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Dear Eskimo

Thanks for your reply very much!

I get a lot of very important informations from your reply as following:

Even if you use a background task to continue long transfers, it's still important that your app support resumable transfers. There are numerous situations where this might be useful:

if it's running on a device that doesn't support multitasking

if the network connection is interrupted during the transfer

if your app asks to start a background task and the system refuses to do so (that is, if -[UIApplication beginBackgroundTaskWithExpirationHandler:] returns UIBackgroundTaskInvalid)

if system resources get low and thus the system must suspend or terminate your app before its background tasks are complete

if the transfer takes more time than the background task will allow

Return back to my question, according to the information above, can I think the URLSession can not be kept for ever because of some reasons such as "if your app asks to start a background task and the system refuses to do so", or "if system resources get low and thus the system must suspend or terminate your app before its background tasks are complete" and so on ?

• Could you please tell me why "the system refuses to do so" ?

• What is the detail conditions of "if system resources get low" , which means low battery, low memory or some other reason?

• In my experiment, the URLSession communication will be stopped suddenly and restarted suddenly, could you please tell me how long the URLSession communication will take from stop to start normally?

Best Regards,

Your specific questions don’t have answers. Well, the answer is that we don’t document the specific conditions under which the system will or won’t start background activities. That’s because the algorithm used to determine this is an implementation detail that changes from release to release.

I think you missed the key point of the post I referenced, namely this:

If you’re uploading small amounts of data and you want low latency, you can prevent your application from suspending and use a standard session. … Or you can use a hybrid approach, where you first try a standard session and then revert to a background session if you run out of time.

If latency is important and you’re transferring a small amount of data, don’t use a background session. Or rather, don’t start off using a background session. Rather, use a UIApplication background task to keep your process away for a short period of time and use that time to attempt an upload using a standard session.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Dear Eskimo

Thank you very much!

About the key point you mentioned above, you suggested me to use a standard session to upload a small amounts of data. But Instead of sending data only once, my system is hoped to send data in the background periodically and contineously.

Do you think my system can work well without background session or using the hybrid approach?

Best Regard

But Instead of sending data only once, my system is hoped to send data in the background periodically and contineously.

Right. But presumably something is causing your app to run in the background in order to generate that data. That mechanism will give you background execution time to run your networking. Or maybe it won’t. The exact details of the execution time given to you by Core Bluetooth are not something I’m familiar with.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Dear Eskimo

Thanks a lot!

As I introduced at the beginning, my program receives the Beacon's signal every second as a trigger to call Corelocation's handler, in which the URLSession (dataTask) is used to forward data received from Beacon to sever.

And for each communication with server, only several bytes data ( small amount of data) is sent to server.

The prcessing from receiving the Beacon's signal to Call Corelocation's handler seems no problem and can be kept foever in background.

And my problem is that URLSession (dataTask) is usually stopped and restarted suddenly in background, although only small amount of data is sent each time, which is send periodly and not sent without intervals.

 That mechanism will give you background execution time to run your networking. Or maybe it won’t.

You means is sometimes my program(URLSession communication) can not be excuted for some reason(some mechanism in iOS)?

Best Regards

And my problem is that URLSession (dataTask) is usually stopped and restarted suddenly in background

Are you using a UIApplication background task to keep your app running while the request is in flight?

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

Dear Eskimo

Thanks for your reply very much!

Are you using a UIApplication background task to keep your app running while the request is in flight?

The "UIApplication background task" you wrote above meant the API such as "UIApplication.shared.beginBackgroundTask()"?

My program is shown in following:

let config:URLSessionConfiguration = URLSessionConfiguration.background(withIdentifier: "abcd")
self.session = URLSession(configuration: config, delegate: nil, delegateQueue: nil)
let task: URLSessionDataTask = session!.dataTask(with: myRequest as URLRequest)
task.resume()

Hope to continue to get your help！

The "UIApplication background task" you wrote above meant the API such as "UIApplication.shared.beginBackgroundTask()"?

Yes. See my UIApplication Background Task Notes post for a whole bunch o’ backstory on that.

My program is shown in following:

OK. That’s running your task is a background session and my advice is that you explore running in a standard session.

Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"