Foundation in -[_NSXPCDistantObject methodSignatureForSelector:]

App & System Services Networking
ninja31312
ninja31312 OP
Created Apr ’16
Replies 15
Boosts 0
Views 7.9k
Participants

We encountered a large number of crashes about XPC reported by our tool, but we could not reproduce it.

All we know is that

- App crashes on iOS8 or iOS9.

- App crashes while it backed from background to foreground.

- There are something happened between com.apple.nsurlsessiond and our app.


Here is the crash log.


Date/Time: 2016-04-21T17:32:24Z
OS Version: iPhone OS 9.2.1 (13D15)
Report Version: 104
Exception Type: SIGABRT
Exception Codes: #0 at 0x18107c140
Crashed Thread: 0
Application Specific Information: *** Terminating app due to uncaught exception 'NSInvalidArgumentException',
reason: '*** -[_NSXPCDistantObject methodSignatureForSelector:]: No protocol has been set on connection <NSXPCConnection: 0x1471921a0> connection to service named com.apple.nsurlsessiond'
Last Exception Backtrace: 0
CoreFoundation 0x00000001814d9900 __exceptionPreprocess + 124 1 
libobjc.A.dylib 0x0000000180b47f80 objc_exception_throw + 56 2 
CoreFoundation 0x00000001814d9848 +[NSException raise:format:] + 120 3 
Foundation 0x0000000181dace7c -[_NSXPCDistantObject methodSignatureForSelector:] + 376 4 
CoreFoundation 0x00000001814dd324 ___forwarding___ + 212 5 
CoreFoundation 0x00000001813e168c _CF_forwarding_prep_0 + 92 6 
CoreFoundation 0x000000018147efc4 __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 20 7 
CoreFoundation 0x000000018147e7e4 _CFXRegistrationPost + 396 8 
CoreFoundation 0x000000018147e564 ___CFXNotificationPost_block_invoke + 60 9 
CoreFoundation 0x00000001814e3de4 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1532 10 
CoreFoundation 0x00000001813bf0f4 _CFXNotificationPost + 368 11 
Foundation 0x0000000181daed2c -[NSNotificationCenter postNotificationName:object:userInfo:] + 68 12 
UIKit 0x000000018644f9f8 -[UIApplication _sendWillEnterForegroundCallbacks] + 264 13 
UIKit 0x0000000186489988 -[UIApplication _handleApplicationActivationWithScene:transitionContext:completion:] + 1752 14 
UIKit 0x0000000186489038 -[UIApplication _handleApplicationLifecycleEventWithScene:transitionContext:completion:] + 448 15 
UIKit 0x0000000186473588 __70-[UIApplication scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke + 152 16 
UIKit 0x0000000186473210 -[UIApplication scene:didUpdateWithDiff:transitionContext:completion:] + 712 17 
FrontBoardServices 0x0000000182a8f790 -[FBSSerialQueue _performNext] + 184 18 
FrontBoardServices 0x0000000182a8fb10 -[FBSSerialQueue _performNextFromRunLoopSource] + 56 19 
CoreFoundation 0x0000000181490efc __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24 20 
CoreFoundation 0x0000000181490990 __CFRunLoopDoSources0 + 540 21 
CoreFoundation 0x000000018148e690 __CFRunLoopRun + 724 22 
CoreFoundation 0x00000001813bd680 CFRunLoopRunSpecific + 384 23
GraphicsServices 0x00000001828cc088 GSEventRunModal + 180 24 
UIKit 0x0000000186234d90 UIApplicationMain + 204 25


Does anyone know the root cause of this crash ?

Replies  15
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Apple Staff, DTS Engineer
DTS Engineer OP
Apple
Apr ’16

By an amazing coincidence I’ve been working with another developer (s. 639,485,677) who has bumped into this problem. At this point my best guess is that this is a bug in NSURLSession’s background session support. I believe it’s been around for a while (since NSURLSession background sessions were introduced in iOS 7) but folks seem to be hitting it more often now.

I’ve asked my other developer to file a bug report about this, but I haven’t yet heard back from them, so I’m going to ask you to do the same: please file a bug report about this then post your bug number here.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"
0
ninja31312
ninja31312 OP
Apr ’16

I created a bug report 25899758 for this issue. Thank you for your help !

0
Apple Staff, DTS Engineer
DTS Engineer OP
Apple
May ’16

ninja31312 wrote:

I created a bug report 25899758 for this issue.

Thanks. By now you’ll know that your bug was closed as a dup of another bug (r. 24449114). I had cause to dig into that bug and I believe that I know what’s going on. I forgot to loop back here to post an update; sorry.

AFAICT this crash is caused by NSURLSession’s background session support. This passes work to its daemon (

nsurlsessiond
) using NSXPCConnection (not part of the iOS SDK, but public API on OS X, so you can read up about it there). NSXPCConnection has the notion of interrupted connections, that is, the IPC connection between the client and the server has torn but can be re-established. NSURLSession’s background session support, like all NSXPCConnection clients, must handle these interruptions as a matter of course.

Alas, there’s a bug in the way it does that. This bug is a race condition that manifest itself as this crash. We hope to fix this in a future OS release but I can’t share any concrete details.

robotive wrote:

Do you think this is related?

No. The above-mentioned crash is specific to NSXPCConnection based on the 

No protocol has been set on connection
message. Your case looks like a standard ‘dangling notification’ problem, that is, some object has registered for a 
UIApplicationDidEnterBackgroundNotification
and then been deallocated without unregistering.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"

WWDC runs Mon, 13 Jun through to Fri, 17 Jun. During that time all of DTS will be at the conference, helping folks out face-to-face. http://developer.apple.com/wwdc/

0
morimoto
morimoto OP
Jun ’16

We were able to resolve this issue simply by switching to ephemeralSessionConfiguration in-place:

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration ephemeralSessionConfiguration];


An obvious fix in hindsight, but when we found our crash, with code we weren't familiar with, it wasn't clear.

Hope this helps some others shortcut if they are able to use it.

0
dive
dive OP
Oct ’16

Hi, eskimo! Thank you for the information.

Can you confirm or deny that the issue is fixed in iOS 10? As far as I can see from our statistics it's still here for iOS 9.3.5, but no crashes for iOS 10.


Thanks!

Artem

0
Apple Staff, DTS Engineer
DTS Engineer OP
Apple
Oct ’16

Can you confirm or deny that the issue is fixed in iOS 10?

It was reported as fixed in iOS 10.

As far as I can see from our statistics it's still here for iOS 9.3.5, but no crashes for iOS 10.

Cool. It looks like the patch stuck (-:

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"
0
dive
dive OP
Oct ’16

Thanks a lot, eskimo!

0
Apple Staff, DTS Engineer
DTS Engineer OP
Apple
Oct ’16

Fabric.io reports that this issue still appears in both iOS 10.0.1 and 10.0.2.

Are you sure it’s exactly the same issue? I’ve seen 10.x reports of similar looking issues with a subtly different backtrace.

Regardless, if you’re app is crashing with errors like this and you believe that you’re using NSURLSession correctly, you should file your own bug report about it. Please post your bug number, just for the record.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"
0
Apple Staff, DTS Engineer
DTS Engineer OP
Apple
Nov ’16

ephemeralSessionConfiguration is available from iOS10+

What makes you say that? 

+ephemeralSessionConfiguration
has been present since NSURLSession was introduce in iOS 7.

Ah, I see, the API Reference page for 

+ephemeralSessionConfiguration
says “iOS 10.0+”. This is simply wrong. I’ve filed a bug about that (r. 29107609). Sorry about the mixup.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"
0
Apple Staff, DTS Engineer
DTS Engineer OP
Apple
Nov ’16

I don't see this bug on [Apple Bug Reporter].

Right. In general you can only see the bug reports that you file yourself; that’s one of the reasons I generally ask folks to file their own bug reports.

I post bug numbers like this so that Future Quinn™ has a reference for this issue when folks ask about it in the… well… future.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware 

let myEmail = "eskimo" + "1" + "@apple.com"
0
ninja31312
ninja31312 OP
Jan ’17

Thank you very much! Eskimo. 🙂

This issue is solved in iOS 10.

0
Foundation in -[_NSXPCDistantObject methodSignatureForSelector:]
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