This post is from the WWDC26 SwiftUI Q&A.
We've been getting stack overflows in code we don't control, in the background AsyncRenderer thread in a chain of calls to updateInheritedViewAsync. But the stack is less than 200 calls deep, presumably because it's a background thread with a smaller stack limit. Is it possible to adjust AsyncRenderer's stack limit? Or otherwise, what limits should we be aware of to prevent running into this issue?
com.apple.SwiftUI.AsyncRenderer: EXC_BAD_ACCESS (code=2, address=0x16f5ebe30)
#0 0x000000019c6b4460 in function signature specialization <Arg[3] = Dead> of static SwiftUI.DisplayList.ViewUpdater.Model.merge(item: inout SwiftUI.DisplayList.Item, index: SwiftUI.DisplayList.Index, into: inout SwiftUI.DisplayList.ViewUpdater.Model.State) -> SwiftUI.DisplayList.ViewUpdater.Model.MergedViewRequirements ()
#1 0x000000019c7c2850 in SwiftUI.DisplayList.ViewUpdater.updateInheritedViewAsync(platform: SwiftUI.DisplayList.ViewUpdater.Platform, oldItem: SwiftUI.DisplayList.Item, oldParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>, newItem: SwiftUI.DisplayList.Item, newParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>) -> Swift.Optional<SwiftUI.Time> ()
#2 0x000000019c7c3ef0 in SwiftUI.DisplayList.ViewUpdater.updateInheritedViewAsync(platform: SwiftUI.DisplayList.ViewUpdater.Platform, oldItem: SwiftUI.DisplayList.Item, oldParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>, newItem: SwiftUI.DisplayList.Item, newParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>) -> Swift.Optional<SwiftUI.Time> ()
#3 0x000000019c7c3ef0 in SwiftUI.DisplayList.ViewUpdater.updateInheritedViewAsync(platform: SwiftUI.DisplayList.ViewUpdater.Platform, oldItem: SwiftUI.DisplayList.Item, oldParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>, newItem: SwiftUI.DisplayList.Item, newParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>) -> Swift.Optional<SwiftUI.Time> ()
#4 0x000000019c7c3ef0 in SwiftUI.DisplayList.ViewUpdater.updateInheritedViewAsync(platform: SwiftUI.DisplayList.ViewUpdater.Platform, oldItem: SwiftUI.DisplayList.Item, oldParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>, newItem: SwiftUI.DisplayList.Item, newParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>) -> Swift.Optional<SwiftUI.Time> ()
...
#147 0x000000019c7c364c in SwiftUI.DisplayList.ViewUpdater.updateInheritedViewAsync(platform: SwiftUI.DisplayList.ViewUpdater.Platform, oldItem: SwiftUI.DisplayList.Item, oldParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>, newItem: SwiftUI.DisplayList.Item, newParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>) -> Swift.Optional<SwiftUI.Time> ()
#148 0x000000019c7c2074 in SwiftUI.DisplayList.ViewUpdater.updateAsync(platform: SwiftUI.DisplayList.ViewUpdater.Platform, oldList: SwiftUI.DisplayList, oldParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>, newList: SwiftUI.DisplayList, newParentState: Swift.UnsafePointer<SwiftUI.DisplayList.ViewUpdater.Model.State>) -> Swift.Optional<SwiftUI.Time> ()
#149 0x000000019c7c1a78 in renderAsync ()
#150 0x000000019c60fc68 in renderDisplayList ()
#151 0x000000019c612094 in protocol witness for SwiftUI.ViewGraphRenderHost.renderDisplayList(_: SwiftUI.DisplayList, asynchronously: Swift.Bool, time: SwiftUI.Time, nextTime: SwiftUI.Time, targetTimestamp: Swift.Optional<SwiftUI.Time>, version: SwiftUI.DisplayList.Version, maxVersion: SwiftUI.DisplayList.Version) -> SwiftUI.Time in conformance SwiftUI.ViewGraph : SwiftUI.ViewGraphRenderHost in SwiftUI ()
#152 0x000000019c7c0dd0 in renderAsync ()
#153 0x000000019c7be6c8 in SwiftUI.ViewGraphHost.displayLinkTimer(timestamp: SwiftUI.Time, targetTimestamp: SwiftUI.Time, isAsyncThread: Swift.Bool) -> () ()
#154 0x000000019c7beab8 in SwiftUI.ViewGraphDisplayLink.displayLinkTimer(__C.CADisplayLink) -> () ()
#155 0x000000019c7be5a8 in @objc SwiftUI.ViewGraphDisplayLink.displayLinkTimer(__C.CADisplayLink) -> () ()
#156 0x0000000192fdbb24 in CA::Display::DisplayLinkItem::dispatch_ ()
#157 0x0000000192fb9164 in CA::Display::DisplayLink::dispatch_items ()
#158 0x0000000192f91870 in display_timer_callback ()
#159 0x000000019256d4cc in __CFMachPortPerform ()
#160 0x000000019259d0b0 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
#161 0x000000019259cfd8 in __CFRunLoopDoSource1 ()
#162 0x0000000192574c1c in __CFRunLoopRun ()
#163 0x0000000192573a6c in _CFRunLoopRunSpecificWithOptions ()
#164 0x0000000190533f54 in -[NSRunLoop(NSRunLoop) runMode:beforeDate:] ()
#165 0x000000018fb9a51c in -[NSRunLoop(NSRunLoop) run] ()
#166 0x000000019c7cd5b0 in function signature specialization <Arg[1] = Dead> of static SwiftUI.ViewGraphDisplayLink.asyncThread(arg: Swift.Optional<Any>) -> () ()
#167 0x000000019c7cd288 in @objc static SwiftUI.ViewGraphDisplayLink.asyncThread(arg: Swift.Optional<Any>) -> () ()
#168 0x000000018fbf321c in __NSThread__start__ ()
#169 0x00000001ef0d044c in _pthread_start ()
Hey! That shouldn't happen. Could you please file a feedback, (here are some great tips how to file a feedback), ideally with steps to reproduce? Small reproducer would be ideal but full project or even just the binary should work here with what actions trigger the issue.
Thank you!
