okla
1
Some users of my app report that it crashes on launch. In Xcode (13) Organizer I see a lot of crashes titled
Protocol witness for Decodable.init(from:) in conformance Library.State + 20
Library.State is a simple struct with two fields that conforms to Codable (I don't override its methods). Is it a bug on my side or in JSONDecoder?
Here is a sample crash report
Hardware Model: iPhone12,3
Process: App [10894]
Path: /private/var/containers/Bundle/Application/2E147D70-2F05-46B0-BD4D-608F3DA7B7FC/App.app/App
Identifier: Developer.App
Version: 509 (3)
AppStoreTools: 12E506
AppVariant: 1:iPhone12,3:14
Beta: YES
Code Type: ARM-64 (Native)
Role: unknown
Parent Process: launchd [1]
Coalition: Developer.App [2507]
Date/Time: 2021-08-01 00:53:51.8245 +0200
Launch Time: 2021-08-01 00:53:45.2800 +0200
OS Version: iPhone OS 15.0 (19A5307g)
Release Type: Beta
Baseband Version: 2.50.05
Report Version: 104
Exception Type: EXC_CRASH (SIGKILL)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Triggered by Thread: 0
Kernel Triage:
VM - pmap_enter failed with resource shortage
VM - pmap_enter failed with resource shortage
VM - pmap_enter failed with resource shortage
VM - pmap_enter failed with resource shortage
VM - pmap_enter failed with resource shortage
Thread 0 name:
Thread 0 Crashed:
0 libswiftCore.dylib 0x00000001892029c8 swift::metadataimpl::ValueWitnesses<swift::metadataimpl::ObjCRetainableBox>::destroy(swift::OpaqueValue*, swift::TargetMetadata<swift::InProcess> const*) + 0 (MetadataImpl.h:146)
1 libswiftFoundation.dylib 0x0000000188ba1df8 _JSONUnkeyedDecodingContainer.decode<A>(_:) + 2276 (JSONEncoder.swift:1990)
2 libswiftFoundation.dylib 0x0000000188ba3778 protocol witness for UnkeyedDecodingContainer.decode<A>(_:) in conformance _JSONUnkeyedDecodingContainer + 16 (<compiler-generated>:0)
3 libswiftCore.dylib 0x0000000188eefbc4 Dictionary<>.init(from:) + 4116 (Codable.swift:5622)
4 libswiftCore.dylib 0x0000000188ef0454 protocol witness for Decodable.init(from:) in conformance <> [A : B] + 40 (<compiler-generated>:0)
5 libswiftCore.dylib 0x00000001891c33d4 dispatch thunk of Decodable.init(from:) + 32
6 libswiftFoundation.dylib 0x0000000188b7de88 __JSONDecoder.unbox_(_:as:) + 1268 (JSONEncoder.swift:2546)
7 libswiftFoundation.dylib 0x0000000188b7ab34 _JSONKeyedDecodingContainer.decode<A>(_:forKey:) + 848 (JSONEncoder.swift:2521)
8 libswiftFoundation.dylib 0x0000000188b8453c protocol witness for KeyedDecodingContainerProtocol.decode<A>(_:forKey:) in conformance _JSONKeyedDecodingContainer<A> + 56
9 libswiftFoundation.dylib 0x0000000188b823d4 protocol witness for KeyedDecodingContainerProtocol.decode<A>(_:forKey:) in conformance _JSONKeyedDecodingContainer<A> + 36
10 libswiftCore.dylib 0x0000000188edc21c _KeyedDecodingContainerBox.decode<A, B>(_:forKey:) + 520 (Codable.swift:4324)
11 libswiftCore.dylib 0x0000000188ecc5ac KeyedDecodingContainer.decode<A>(_:forKey:) + 68 (Codable.swift:1759)
12 App 0x0000000100a54af8 specialized Library.State.init(from:) + 256 (<compiler-generated>:0)
13 App 0x0000000100a50334 Library.State.init(from:) + 4 (<compiler-generated>:0)
14 App 0x0000000100a50334 protocol witness for Decodable.init(from:) in conformance Library.State + 20
15 libswiftCore.dylib 0x00000001891c33d4 dispatch thunk of Decodable.init(from:) + 32
16 libswiftFoundation.dylib 0x0000000188b7de88 __JSONDecoder.unbox_(_:as:) + 1268 (JSONEncoder.swift:2546)
17 libswiftFoundation.dylib 0x0000000188b697f8 JSONDecoder.decode<A>(_:from:) + 1332 (JSONEncoder.swift:2521)
18 libswiftFoundation.dylib 0x0000000188ba2948 dispatch thunk of JSONDecoder.decode<A>(_:from:) + 56
19 App 0x0000000100a7edd0 0x100a3c000 + 273872
20 SwiftUI 0x000000018bfbc418 static App.main() + 112 (App.swift:114)
21 App 0x0000000100a4869c 0x100a3c000 + 50844
22 dyld 0x0000000100b719e4 start + 520 (dyldMain.cpp:876)
Thread 1:
0 libsystem_pthread.dylib 0x00000001f3ddfdf4 0x1f3ddf000 + 3572
Thread 0 crashed with ARM Thread State (64-bit):
x0: 0x000000016f3c2ab0 x1: 0x00000001dea5b680 x2: 0x00000001dea59fe0 x3: 0x00000001892029c8
x4: 0x000000016f3c2958 x5: 0x000000016f3c2950 x6: 0x0000000000000001 x7: 0x0000000000000000
x8: 0x0000000000000001 x9: 0x0000000189201eec x10: 0x0000000001000000 x11: 0x000f000282bd0100
x12: 0x0000000000000007 x13: 0x0000000282bd0160 x14: 0x00000000e6cfe800 x15: 0x00000001dd91c408
x16: 0x04f80001dea59fe0 x17: 0x00000001dea59fd8 x18: 0x0000000000000000 x19: 0x000000016f3c29d0
x20: 0x0000000000000000 x21: 0x0000000000000000 x22: 0x00000001dea54e78 x23: 0x0000000000000003
x24: 0x00000001dea4fc98 x25: 0x00000001dea54e78 x26: 0x000000016f3c29a0 x27: 0x00000001dea59b08
x28: 0x0000000000000000 fp: 0x000000016f3c2bc0 lr: 0x0000000188ba1df8
sp: 0x000000016f3c2990 pc: 0x00000001892029c8 cpsr: 0x60000000
esr: 0x56000080 Address size fault
Binary Images:
0x100a3c000 - 0x100a97fff App arm64 <0412067b611237958e315d06d3fb80c9> /private/var/containers/Bundle/Application/2E147D70-2F05-46B0-BD4D-608F3DA7B7FC/App.app/App
0x100b58000 - 0x100baffff dyld arm64e <307ca1e7c12f31918ff5dbe126e7126a> /usr/lib/dyld
0x188b5d000 - 0x188e76fff libswiftFoundation.dylib arm64e <c8327e88a8d43d97be98616e89464fc2> /usr/lib/swift/libswiftFoundation.dylib
0x188e77000 - 0x1892c8fff libswiftCore.dylib arm64e <fe7d9e7294d53dc9877859b76410590a> /usr/lib/swift/libswiftCore.dylib
0x18be67000 - 0x18ce4afff SwiftUI arm64e <a25f98b4f2bc331ab68a42fb2ed42ca5> /System/Library/Frameworks/SwiftUI.framework/SwiftUI
0x1f3ddf000 - 0x1f3deafff libsystem_pthread.dylib arm64e <db2e203d50373d1d9c6d31955d713197> /usr/lib/system/libsystem_pthread.dylib
EOF
okla
2
Well, maybe Library.State is not so simple for the compiler/JSONDecoder?
enum Library {
typealias History = [UInt64]
typealias Snapshot = [UInt64: Item.Snapshot]
struct State: Codable, Equatable {
let snapshot: Snapshot
let history: History
}
}
extension Item {
struct Snapshot: Equatable, Codable {
let pc: Int
let lp: TimeInterval?
}
}
tera
3
would be super handy to see the corresponding json that causes this crash.
okla
4
Unfortunately, I can't reproduce this on my devices. All I have is the code and crash reports. Also, JSONDecoder().decode() call is used with try? so JSON can be any and still shouldn't crash, isn't it?
I have also run into this kind of crash. But I haven't been able to get a reliable test case to report it in a meaningful way.
In my experience decoding the same object will work the majority of the time and then sometimes it just fails. The only difference I've been able to tell is that the functions on the stack are different. And this is all in Swift/Combine/SwiftUI land not our app directly dropping to unsafe operations.
Jon_Shier
(Jon Shier)
6
This looks like a Swift runtime crash, so you can report it to bugs.swift.org without a reproducer. These sorts of crashes happen semi-regularly and there isn't much to do about them except report and hope they get prioritized and investigated. You'll want to include the version of Xcode / Swift you used to compile the crashing version as well.
