unsubscribe on channel enumeration causing crash

[mattheworiordan]

Which version of the Ably SDK are you using?

github "ably/ably-ios" == 1.1.2

On which platform does the issue happen?

iOS 12

What did you do?

        channels.forEach {
            ablyClient.channels.get($0).unsubscribe()
        }

What did you expect to happen?

Not a crash!

What happened instead?

[ricardopereira]

realtime.channels.get("groups").subscribe("foo", onAttach: { error in
    self.realtime.channels.get("groups").unsubscribe() //<-- crash
}, callback: { message in
    print(message)
})

^ this will crash with a EXC_BAD_INSTRUCTION (SIGTRAP).

Stack trace:

#0	0x000000010efa10c7 in __DISPATCH_WAIT_FOR_QUEUE__ ()
#1	0x00007000052f1e90 in 0x7000052f1e90 ()
#2	0x000000010efa0ab9 in _dispatch_sync_f_slow ()
#3	0x000000010bf8c18c in -[ARTChannels getChannel:options:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTChannels.m:80
#4	0x000000010bf8bd0b in -[ARTChannels get:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTChannels.m:61
#5	0x000000010c00f99e in -[ARTRealtimeChannels get:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTRealtimeChannels.m:52
#6	0x000000010b852412 in closure #1 in ViewController.sendNotificationButtonTapped(_:) at /Users/mac/dev/ably-experiments/source/ViewController.swift:57
#7	0x000000010b8524ad in partial apply for closure #1 in ViewController.sendNotificationButtonTapped(_:) ()
#8	0x000000010b8524f2 in thunk for @escaping @callee_guaranteed (@guaranteed ARTErrorInfo?) -> () ()
#9	0x000000010bf9dbb3 in __24-[ARTEventEmitter once:]_block_invoke at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTEventEmitter.m:227
#10	0x000000010c8e8706 in -[__NSObserver _doit:] ()
#11	0x000000010de0e5ec in __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ ()
#12	0x000000010de0da6f in _CFXRegistrationPost ()
#13	0x000000010de0d7b3 in ___CFXNotificationPost_block_invoke ()
#14	0x000000010def15e2 in -[_CFXNotificationRegistrar find:object:observer:enumerator:] ()
#15	0x000000010de0d101 in _CFXNotificationPost ()
#16	0x000000010c8e8eaf in -[NSNotificationCenter postNotificationName:object:userInfo:] ()
#17	0x000000010bf9e8d3 in -[ARTEventEmitter emit:with:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTEventEmitter.m:275
#18	0x000000010c0020d5 in -[ARTRealtimeChannel setAttached:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTRealtimeChannel.m:658
#19	0x000000010c000f0e in -[ARTRealtimeChannel onChannelMessage:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTRealtimeChannel.m:590
#20	0x000000010bfe7ee0 in -[ARTRealtime onChannelMessage:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTRealtime.m:938
#21	0x000000010bff07b3 in -[ARTRealtime realtimeTransport:didReceiveMessage:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTRealtime.m:1328
#22	0x000000010c044e1f in -[ARTWebSocketTransport receive:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTWebSocketTransport.m:106
#23	0x000000010c044eee in -[ARTWebSocketTransport receiveWithData:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTWebSocketTransport.m:111
#24	0x000000010c047d74 in -[ARTWebSocketTransport webSocketMessageData:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTWebSocketTransport.m:366
#25	0x000000010c0478d0 in -[ARTWebSocketTransport webSocket:didReceiveMessage:] at /Users/mac/dev/ably-experiments/Pods/Ably/Source/ARTWebSocketTransport.m:348
#26	0x000000010d382b02 in __43-[SRWebSocket _handleFrameWithData:opCode:]_block_invoke.252 at /Users/mac/dev/ably-experiments/Pods/SocketRocketAblyFork/SocketRocket/SRWebSocket.m:829

The onAttachCallback is probably calling the block in the internal queue and it's wrong.

[mattheworiordan]

is probably calling the block in the internal queue and it's wrong.

Thanks for investifgating. @ricardopereira are you saying thtat that's fault though in the SDK or the caller. I would argue that whilst odd, it's still valid.

[ricardopereira]

@mattheworiordan It's a SDK issue. All user callbacks should use the user queue, not the internal one.

[mattheworiordan]

It's a SDK issue

Ok.

[ricardopereira]

@mattheworiordan Fix has been implemented. Just waiting for the CI.