[Webkit-unassigned] [Bug 217183] New: [iOS 14] Hang in -[WKUserDefaults _notifyObserversOfChangeFromValuesForKeys:toValuesForKeys:]

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=217183

            Bug ID: 217183
           Summary: [iOS 14] Hang in -[WKUserDefaults
                    _notifyObserversOfChangeFromValuesForKeys:toValuesForK
                    eys:]
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKit API
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: ajuma at chromium.org
                CC: pvollan at apple.com

Chrome for iOS is getting a significant number of hang reports in -[WKUserDefaults _notifyObserversOfChangeFromValuesForKeys:toValuesForKeys:] on iOS 14.

This code was added in bug 203420.

We don't have steps to reproduce, but the reports suggest that this happens after the app is backgrounded.

Here's the stack:
(libobjc.A.dylib)       class_conformsToProtocol
(libobjc.A.dylib)       +[NSObject conformsToProtocol:]
(Foundation)            -[NSCoder validateClassSupportsSecureCoding:]
(Foundation)            _encodeObject
(Foundation)            +[NSKeyedArchiver archivedDataWithRootObject:requiringSecureCoding:error:]
(WebKit)                -[WKUserDefaults _notifyObserversOfChangeFromValuesForKeys:toValuesForKeys:]
(CoreFoundation)        -[CFPrefsSource forEachObserver:]
(CoreFoundation)        -[CFPrefsSource _notifyObserversOfChangeFromValuesForKeys:toValuesForKeys:]
(CoreFoundation)        ___CFPrefsDeliverPendingKVONotificationsGuts_block_invoke
(CoreFoundation)        __CFDictionaryApplyFunction_block_invoke
(CoreFoundation)        CFBasicHashApply
(CoreFoundation)        CFDictionaryApplyFunction
(CoreFoundation)        _CFPrefsDeliverPendingKVONotificationsGuts
(CoreFoundation)        __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__
(CoreFoundation)        __CFRunLoopDoBlocks
(CoreFoundation)        __CFRunLoopRun
(CoreFoundation)        CFRunLoopRunSpecific
(GraphicsServices)      GSEventRunModal
(UIKitCore)             -[UIApplication _run]
(UIKitCore)             UIApplicationMain

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