I've implemented a Widget Extension (i.e. an iOS 14 widget, using WidgetKit) for my app. Ordinarily the widget works just fine, but occasionally it'll get into a state where it flickers repeatedly and eventually just freezes. I've tried connecting a debugger to the widget process, but it doesn't catch any crashes or exceptions. However I did see in my device logs repeated crashes (~25 over the course of one minute) in the chronod process. The reports all look basically the same:
Incident Identifier: ...
CrashReporter Key: ...
Hardware Model: iPhone10,3
Process: chronod [96919]
Path: /System/Library/PrivateFrameworks/ChronoCore.framework/Support/chronod
Identifier: chronod
Version: ???
Code Type: ARM-64 (Native)
Role: Unspecified
Parent Process: launchd [1]
Coalition: com.apple.chronod [443]
Date/Time: 2020-09-30 13:41:06.1434 -0700
Launch Time: 2020-09-30 13:41:05.6902 -0700
OS Version: iPhone OS 14.0 (18A373)
Release Type: User
Baseband Version: 6.02.01
Report Version: 104
Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000001, 0x0000000197017d08
Termination Signal: Trace/BPT trap: 5
Termination Reason: Namespace SIGNAL, Code 0x5
Terminating Process: exc handler [96919]
Triggered by Thread: 0
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0 SwiftUI 0x0000000197017d08 CodablePlatformFont.init+ 6647048 (from:) + 2744
1 SwiftUI 0x0000000197017a00 CodablePlatformFont.init+ 6646272 (from:) + 1968
2 SwiftUI 0x0000000197017d34 protocol witness for Decodable.init+ 6647092 (from:) in conformance CodablePlatformFont + 20
3 libswiftCore.dylib 0x0000000194548f80 dispatch thunk of Decodable.init+ 2957184 (from:) + 16
4 libswiftFoundation.dylib 0x0000000194162ccc __PlistDecoder.unbox<A>+ 326860 (_:as:) + 372
5 libswiftFoundation.dylib 0x000000019416d820 _PlistKeyedDecodingContainer.decode<A>+ 370720 (_:forKey:) + 660
6 libswiftFoundation.dylib 0x000000019416fc54 protocol witness for KeyedDecodingContainerProtocol.decode<A>+ 379988 (_:forKey:) in conformance _PlistKeyedDecodingContainer<A> + 48
7 libswiftFoundation.dylib 0x000000019416f9b4 protocol witness for KeyedDecodingContainerProtocol.decode<A>+ 379316 (_:forKey:) in conformance _PlistKeyedDecodingContainer<A> + 20
8 libswiftCore.dylib 0x00000001942cb2cc _KeyedDecodingContainerBox.decode<A, B>+ 344780 (_:forKey:) + 296
9 libswiftCore.dylib 0x00000001942be9e4 KeyedDecodingContainer.decode<A>+ 293348 (_:forKey:) + 40
10 SwiftUI 0x0000000197014374 CodableAttributes.init+ 6632308 (from:) + 832
11 SwiftUI 0x0000000197015170 protocol witness for Decodable.init+ 6635888 (from:) in conformance CodableAttributes + 20
12 libswiftCore.dylib 0x0000000194548f80 dispatch thunk of Decodable.init+ 2957184 (from:) + 16
13 libswiftFoundation.dylib 0x0000000194162ccc __PlistDecoder.unbox<A>+ 326860 (_:as:) + 372
14 libswiftFoundation.dylib 0x00000001941702ec _PlistUnkeyedDecodingContainer.decode<A>+ 381676 (_:) + 776
15 libswiftFoundation.dylib 0x0000000194172110 protocol witness for UnkeyedDecodingContainer.decode<A>+ 389392 (_:) in conformance _PlistUnkeyedDecodingContainer + 12
16 libswiftCore.dylib 0x00000001942d5bd0 Array<A>.init+ 388048 (from:) + 332
17 libswiftCore.dylib 0x00000001942d6178 protocol witness for Decodable.init+ 389496 (from:) in conformance <A> [A] + 28
18 libswiftCore.dylib 0x00000001942d5c8c protocol witness for Decodable.init+ 388236 (from:) in conformance <A> [A] + 20
19 libswiftCore.dylib 0x0000000194548f80 dispatch thunk of Decodable.init+ 2957184 (from:) + 16
20 libswiftFoundation.dylib 0x0000000194162ccc __PlistDecoder.unbox<A>+ 326860 (_:as:) + 372
21 libswiftFoundation.dylib 0x000000019416d820 _PlistKeyedDecodingContainer.decode<A>+ 370720 (_:forKey:) + 660
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. (Shortened the stack trace for readability, lots more Plist decoding here)
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153 libswiftCore.dylib 0x00000001942cb2cc _KeyedDecodingContainerBox.decode<A, B>+ 344780 (_:forKey:) + 296
154 libswiftCore.dylib 0x00000001942be9e4 KeyedDecodingContainer.decode<A>+ 293348 (_:forKey:) + 40
155 SwiftUI 0x0000000196bd0560 _ArchivedViewStates.State.init+ 2159968 (from:) + 304
156 SwiftUI 0x0000000196bd08d4 protocol witness for Decodable.init+ 2160852 (from:) in conformance _ArchivedViewStates.State + 20
157 libswiftCore.dylib 0x0000000194548f80 dispatch thunk of Decodable.init+ 2957184 (from:) + 16
158 libswiftFoundation.dylib 0x0000000194162ccc __PlistDecoder.unbox<A>+ 326860 (_:as:) + 372
159 libswiftFoundation.dylib 0x0000000194162a08 PropertyListDecoder.decode<A>+ 326152 (_:fromTopLevel:) + 344
160 libswiftFoundation.dylib 0x000000019416278c PropertyListDecoder.decode<A>+ 325516 (_:from:format:) + 296
161 libswiftFoundation.dylib 0x0000000194162658 PropertyListDecoder.decode<A>+ 325208 (_:from:) + 44
162 libswiftFoundation.dylib 0x00000001941732f4 dispatch thunk of PropertyListDecoder.decode<A>+ 393972 (_:from:) + 20
163 SwiftUI 0x0000000196bd1204 _ArchivedViewStates.state+ 2163204 (at:) + 416
164 WidgetKit 0x0000000196973ab0 0x19693a000 + 236208
165 WidgetKit 0x00000001969748d4 0x19693a000 + 239828
166 WidgetKit 0x00000001969a4794 0x19693a000 + 436116
167 ChronoKit 0x00000001b9999c34 0x1b990d000 + 576564
168 ChronoKit 0x00000001b99b3d20 0x1b990d000 + 683296
169 ChronoKit 0x00000001b99b47a0 0x1b990d000 + 685984
170 ChronoKit 0x00000001b99b4944 0x1b990d000 + 686404
171 ChronoKit 0x00000001b99b17c0 0x1b990d000 + 673728
172 SwiftUI 0x0000000196d22bdc ViewBodyAccessor.body+ 3546076 (of:) + 32
173 SwiftUI 0x0000000196ff87ac closure #1 in DynamicBody.updateValue+ 6518700 () + 156
174 SwiftUI 0x0000000196ff861c DynamicBody.updateValue+ 6518300 () + 1660
175 SwiftUI 0x0000000196d43d8c partial apply for implicit closure #2 in implicit closure #1 in closure #1 in closure #1 in Attribute.init<A>+ 3681676 (_:) + 28
176 AttributeGraph 0x00000001b6bf6064 AG::Graph::UpdateStack::update+ 20580 () + 484
177 AttributeGraph 0x00000001b6bf6474 AG::Graph::update_attribute+ 21620 (AG::data::ptr<AG::Node>, bool) + 328
178 AttributeGraph 0x00000001b6bfb678 AG::Graph::input_value_ref_slow+ 42616 (AG::data::ptr<AG::Node>, AG::AttributeID, unsigned int, AGSwiftMetadata const*, bool*, long) + 380
179 AttributeGraph 0x00000001b6c0c258 AGGraphGetValue + 228
180 SwiftUI 0x0000000196d32cc4 SubscriptionView.ChildAttribute.view.getter + 68
181 SwiftUI 0x0000000196d32ef8 SubscriptionView.ChildAttribute.updateValue+ 3612408 () + 520
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. (Shortened the stack trace for readability, lots more AttributeGraph stuff here)
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222 AttributeGraph 0x00000001b6bf6064 AG::Graph::UpdateStack::update+ 20580 () + 484
223 AttributeGraph 0x00000001b6bf6474 AG::Graph::update_attribute+ 21620 (AG::data::ptr<AG::Node>, bool) + 328
224 AttributeGraph 0x00000001b6bfb678 AG::Graph::input_value_ref_slow+ 42616 (AG::data::ptr<AG::Node>, AG::AttributeID, unsigned int, AGSwiftMetadata const*, bool*, long) + 380
225 AttributeGraph 0x00000001b6c0c258 AGGraphGetValue + 228
226 SwiftUI 0x0000000196d3da50 DynamicPreferenceCombiner.info.getter + 92
227 SwiftUI 0x0000000196d3dc00 DynamicPreferenceCombiner.value.getter + 168
228 SwiftUI 0x0000000196b2cda0 implicit closure #2 in implicit closure #1 in closure #1 in closure #1 in Attribute.init<A>+ 1490336 (_:) + 84
229 AttributeGraph 0x00000001b6bf6064 AG::Graph::UpdateStack::update+ 20580 () + 484
230 AttributeGraph 0x00000001b6bf6474 AG::Graph::update_attribute+ 21620 (AG::data::ptr<AG::Node>, bool) + 328
231 AttributeGraph 0x00000001b6bfb0f4 AG::Graph::value_ref+ 41204 (AG::AttributeID, AGSwiftMetadata const*, bool*) + 152
232 AttributeGraph 0x00000001b6c0c2a0 AGGraphGetValue + 300
233 SwiftUI 0x00000001972a5d38 GraphHost.updatePreferences+ 9325880 () + 52
234 SwiftUI 0x0000000196e32528 ViewGraph.updateOutputs+ 4658472 (at:) + 100
235 SwiftUI 0x0000000197212644 closure #1 in ViewRendererHost.render+ 8721988 (interval:updateDisplayList:) + 1316
236 SwiftUI 0x0000000197211aec ViewRendererHost.render+ 8719084 (interval:updateDisplayList:) + 316
237 SwiftUI 0x000000019735f528 _UIHostingView.layoutSubviews+ 10085672 () + 184
238 SwiftUI 0x000000019735f554 @objc _UIHostingView.layoutSubviews+ 10085716 () + 24
239 UIKitCore 0x0000000193609954 -[UIView+ 16935252 (CALayerDelegate) layoutSublayersOfLayer:] + 2464
240 QuartzCore 0x0000000193b099e8 -[CALayer layoutSublayers] + 288
241 QuartzCore 0x0000000193b0feb4 CA::Layer::layout_if_needed+ 1420980 (CA::Transaction*) + 520
242 QuartzCore 0x0000000193b1b1d0 CA::Layer::layout_and_display_if_needed+ 1466832 (CA::Transaction*) + 140
243 QuartzCore 0x0000000193a67500 CA::Context::commit_transaction+ 730368 (CA::Transaction*, double, double*) + 416
244 QuartzCore 0x0000000193a91698 CA::Transaction::commit+ 902808 () + 728
245 UIKitCore 0x00000001931217ac __34-[UIApplication _firstCommitBlock]_block_invoke_2 + 80
246 CoreFoundation 0x0000000190844fa0 __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 20
247 CoreFoundation 0x0000000190844228 __CFRunLoopDoBlocks + 404
248 CoreFoundation 0x000000019083ea54 __CFRunLoopRun + 796
249 CoreFoundation 0x000000019083e200 CFRunLoopRunSpecific + 572
250 GraphicsServices 0x00000001a6939598 GSEventRunModal + 160
251 UIKitCore 0x0000000193104004 -[UIApplication _run] + 1052
252 UIKitCore 0x00000001931095d8 UIApplicationMain + 164
253 ChronoCore 0x00000001b92b23d4 0x1b922e000 + 541652
254 chronod 0x00000001000ab6a4 0x1000a8000 + 13988
255 libdyld.dylib 0x000000019051d598 start + 4
Thread 1:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 2:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 3:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 4:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 5 name: com.apple.uikit.eventfetch-thread
Thread 5:
0 libsystem_kernel.dylib 0x00000001bb1a38c4 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x00000001bb1a2cc8 mach_msg + 72
2 CoreFoundation 0x000000019084474c __CFRunLoopServiceMachPort + 376
3 CoreFoundation 0x000000019083ebd0 __CFRunLoopRun + 1176
4 CoreFoundation 0x000000019083e200 CFRunLoopRunSpecific + 572
5 Foundation 0x0000000191a48278 -[NSRunLoop+ 33400 (NSRunLoop) runMode:beforeDate:] + 228
6 Foundation 0x0000000191a48158 -[NSRunLoop+ 33112 (NSRunLoop) runUntilDate:] + 88
7 UIKitCore 0x00000001931af9fc -[UIEventFetcher threadMain] + 504
8 Foundation 0x0000000191ba4c48 __NSThread__start__ + 848
9 libsystem_pthread.dylib 0x00000001d6116b70 _pthread_start + 288
10 libsystem_pthread.dylib 0x00000001d611b880 thread_start + 8
Thread 6:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 7:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 8:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 9:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 10:
0 libsystem_pthread.dylib 0x00000001d611b86c start_wqthread + 0
Thread 0 crashed with ARM Thread State (64-bit):
x0: 0x00000001000d7200 x1: 0x0000000000000407 x2: 0x0000000000000407 x3: 0x0000000100384c40
x4: 0x0000000000000020 x5: 0x0000000100384c40 x6: 0x0000000000000002 x7: 0x0000000000000000
x8: 0x091bc10038780055 x9: 0x091bc10038780055 x10: 0x00000000000bcfa0 x11: 0x0000000000003fff
x12: 0x0000000100300000 x13: 0x0000000088c5e050 x14: 0x0000000088c5e014 x15: 0x0000000000003c93
x16: 0x00000001d6106ef0 x17: 0x00000000d0411000 x18: 0x0000000000000000 x19: 0x00000001deab4d20
x20: 0x0000000000000000 x21: 0x0000000000000000 x22: 0x00000001deb92018 x23: 0x0000000100384c70
x24: 0x000000016fd4b640 x25: 0x00000001deaa3f50 x26: 0x0000000106771e00 x27: 0x0000000106771ea0
x28: 0x0000000000000000 fp: 0x000000016fd4b760 lr: 0x0000000197017a00
sp: 0x000000016fd4b630 pc: 0x0000000197017d08 cpsr: 0x60000000
esr: 0xf2000001 Address size fault
So it seems pretty clear that the error has to do with decoding a Font object. I do use custom fonts in my app and widget which is likely relevant, but they show up just fine the first time they're displayed in the widget and I haven't had any issues in my app itself (which doesn't use SwiftUI).
It also looks like the process leading up to the error is the UI state being encoded and cached somewhere, then failing to be decoded for display later on. But none of that code is owned by me, making it exceedingly difficult to debug.
What's going wrong, and how can it be addressed?