Exception: Null Object Reference - Clicking on Button

[piotrzarzycki21]

Another NPE in our application - it occurs much often when I'm clicking on Button. Code of that buttons is here - Button is created in following way

[2024-02-26 10:15:58][FATAL][Genesis/Source/genesis/application/GenesisApplication.hx:557] Fatal exception : Null Object Reference
Details : Exception: Null Object Reference
Called from openfl.text.TextField.__getBounds (openfl/text/TextField.hx line 1807)
Called from openfl.display.DisplayObject.getBounds (openfl/display/DisplayObject.hx line 1184)
Called from openfl.text.TextField.__updateScrollH (openfl/text/TextField.hx line 2304)
Called from openfl.text.TextField.setSelection (openfl/text/TextField.hx line 1380)
Called from openfl.text.TextField.__updateLayout (openfl/text/TextField.hx line 2264)
Called from openfl.text.TextField.get_textWidth (openfl/text/TextField.hx line 3048)
Called from feathers.controls.Button.refreshText (feathers/controls/Button.hx line 1061)
Called from feathers.controls.Button.commitChanges (feathers/controls/Button.hx line 769)
Called from feathers.controls.BasicButton.update (feathers/controls/BasicButton.hx line 223)
Called from genesis.application.components.GenesisButton.update (genesis/application/components/GenesisButton.hx line 46)
Called from feathers.core.ValidatingSprite.validateNow (feathers/core/ValidatingSprite.hx line 289)
Called from feathers.core.FeathersControl.validateNow (feathers/core/FeathersControl.hx line 715)
Called from feathers.controls.LayoutGroup.validateChildren (feathers/controls/LayoutGroup.hx line 900)
Called from feathers.controls.LayoutGroup.update (feathers/controls/LayoutGroup.hx line 568)
Called from feathers.core.ValidatingSprite.validateNow (feathers/core/ValidatingSprite.hx line 289)
Called from feathers.core.FeathersControl.validateNow (feathers/core/FeathersControl.hx line 715)
Called from feathers.controls.LayoutGroup.validateNow (feathers/controls/LayoutGroup.hx line 517)
Called from feathers.core.ValidationQueue.validateNow (feathers/core/ValidationQueue.hx line 156)
Called from feathers.core.ValidationQueue.validationQueue_stage_renderHandler (feathers/core/ValidationQueue.hx line 162)
Called from openfl.events.EventDispatcher.__dispatchEvent (openfl/events/EventDispatcher.hx line 426)
Called from openfl.display.DisplayObject.__dispatch (openfl/display/DisplayObject.hx line 1398)
Called from openfl.display.Stage.__broadcastEvent (openfl/display/Stage.hx line 1187)
Called from openfl.display.Stage.__render (openfl/display/Stage.hx line 2062)
Called from openfl.display.Stage.__onLimeRender (openfl/display/Stage.hx line 2186)
Called from lime.app._Event_lime_graphics_RenderContext_Void.dispatch (lime/_internal/macros/EventMacro.hx line 91)
Called from lime._internal.backend.native.NativeApplication.handleRenderEvent (lime/_internal/backend/native/NativeApplication.hx line 375)
Called from lime._internal.backend.native.NativeApplication.exec (lime/_internal/backend/native/NativeApplication.hx line 146)
Called from lime.app.Application.exec (lime/app/Application.hx line 150)
Called from openfl.display.Application.exec (openfl/display/Application.hx line 130)
Called from ApplicationMain.create (ApplicationMain.hx line 142)
Native : null
Stack : null

[joshtynjala]

Looks like another null value from Rectangle.__pool. This is probably a symptom of the same issue that caused #164.

[piotrzarzycki21]

I got again crash today clicking on same Button, but stack trace look a bit different. Maybe it will be helpful.

[2024-02-28 09:54:05][FATAL][Genesis/Source/genesis/application/GenesisApplication.hx:557] Fatal exception : Null Object Reference
Details : Exception: Null Object Reference
Called from openfl.display.DisplayObject.__dispatchWithCapture (openfl/display/DisplayObject.hx line 1461)
Called from openfl.display.DisplayObject.dispatchEvent (openfl/display/DisplayObject.hx line 1134)
Called from feathers.events.FeathersEvent.dispatch (feathers/events/FeathersEvent.hx line 136)
Called from feathers.controls.dataRenderers.LayoutGroupItemRenderer.set_selected (feathers/controls/dataRenderers/LayoutGroupItemRenderer.hx line 129)
Called from feathers.controls.ListView.refreshItemRendererProperties (feathers/controls/ListView.hx line 1364)
Called from feathers.controls.ListView.updateItemRenderer (feathers/controls/ListView.hx line 1337)
Called from feathers.controls.ListView.findUnrenderedData (feathers/controls/ListView.hx line 1269)
Called from feathers.controls.ListView.refreshItemRenderers (feathers/controls/ListView.hx line 1151)
Called from feathers.controls.supportClasses.AdvancedLayoutViewPort.refreshLayout (feathers/controls/supportClasses/AdvancedLayoutViewPort.hx line 350)
Called from feathers.controls.supportClasses.AdvancedLayoutViewPort.update (feathers/controls/supportClasses/AdvancedLayoutViewPort.hx line 334)
Called from feathers.core.ValidatingSprite.runWithInvalidationFlagsOnly (feathers/core/ValidatingSprite.hx line 183)
Called from feathers.controls.supportClasses.AdvancedLayoutViewPort.update (feathers/controls/supportClasses/AdvancedLayoutViewPort.hx line 329)
Called from feathers.core.ValidatingSprite.validateNow (feathers/core/ValidatingSprite.hx line 289)
Called from feathers.core.FeathersControl.validateNow (feathers/core/FeathersControl.hx line 715)
Called from feathers.controls.supportClasses.BaseScrollContainer.refreshViewPort (feathers/controls/supportClasses/BaseScrollContainer.hx line 1294)
Called from feathers.controls.supportClasses.BaseScrollContainer.update (feathers/controls/supportClasses/BaseScrollContainer.hx line 1105)
Called from feathers.controls.ListView.update (feathers/controls/ListView.hx line 1071)
Called from feathers.core.ValidatingSprite.validateNow (feathers/core/ValidatingSprite.hx line 289)
Called from feathers.core.FeathersControl.validateNow (feathers/core/FeathersControl.hx line 715)
Called from feathers.core.ValidationQueue.validateNow (feathers/core/ValidationQueue.hx line 156)
Called from feathers.core.ValidationQueue.validationQueue_stage_renderHandler (feathers/core/ValidationQueue.hx line 162)
Called from openfl.events.EventDispatcher.__dispatchEvent (openfl/events/EventDispatcher.hx line 426)
Called from openfl.display.DisplayObject.__dispatch (openfl/display/DisplayObject.hx line 1398)
Called from openfl.display.Stage.__broadcastEvent (openfl/display/Stage.hx line 1187)
Called from openfl.display.Stage.__render (openfl/display/Stage.hx line 2062)
Called from openfl.display.Stage.__onLimeRender (openfl/display/Stage.hx line 2186)
Called from lime.app._Event_lime_graphics_RenderContext_Void.dispatch (lime/_internal/macros/EventMacro.hx line 91)
Called from lime._internal.backend.native.NativeApplication.handleRenderEvent (lime/_internal/backend/native/NativeApplication.hx line 375)
Called from lime._internal.backend.native.NativeApplication.exec (lime/_internal/backend/native/NativeApplication.hx line 146)
Called from lime.app.Application.exec (lime/app/Application.hx line 150)
Called from openfl.display.Application.exec (openfl/display/Application.hx line 130)
Called from ApplicationMain.create (ApplicationMain.hx line 142)
Native : null
Stack : null

[joshtynjala]

Interesting! That one also appears to be caused by an ObjectPool returning null, but it's a different ObjectPool this time. Perhaps this means it is a bug in the ObjectPool class.

[piotrzarzycki21]

I just catch that exception in Moonshine debugger. Here is screenshot. Maybe it helps you at some point:

I think stack var is null. Should I do something specific when I catch that again ?

[joshtynjala]

I just made this small change to ObjectPool in Lime: openfl/lime@5f63ef1

If you could try that change in ObjectPool with a debug build, that might help give us some clues.

[piotrzarzycki21]

I just made this small change to ObjectPool in Lime: openfl/lime@5f63ef1

If you could try that change in ObjectPool with a debug build, that might help give us some clues.

Maybe it helped in a way that I got crash doing almost same thing - clicking on button, but exception looks different:

In exception I see following classes ToastManager and Toast

[piotrzarzycki21]

This one came next:

: [2024-03-22 15:29:21][FATAL][Genesis/Source/genesis/application/GenesisApplication.hx:557] Fatal exception : [lime.utils.ObjectPool] ERROR: Object has already been released
: Details : Exception: [lime.utils.ObjectPool] ERROR: Object has already been released
: Called from lime.utils.Log.error (lime/utils/Log.hx line 37)
: Called from lime.utils.ObjectPool.release (lime/utils/ObjectPool.hx line 106)
: Called from openfl.text.TextField.__getBounds (openfl/text/TextField.hx line 1813)
: Called from openfl.display.DisplayObject.getBounds (openfl/display/DisplayObject.hx line 1184)
: Called from openfl.text.TextField.__updateScrollH (openfl/text/TextField.hx line 2304)
: Called from openfl.text.TextField.setSelection (openfl/text/TextField.hx line 1380)
: Called from openfl.text.TextField.__updateLayout (openfl/text/TextField.hx line 2264)
: Called from openfl.text.TextField.get_textWidth (openfl/text/TextField.hx line 3048)
: Called from feathers.controls.Label.refreshText (feathers/controls/Label.hx line 749)
: Called from feathers.controls.Label.update (feathers/controls/Label.hx line 583)
: Called from feathers.core.ValidatingSprite.validateNow (feathers/core/ValidatingSprite.hx line 289)
: Called from feathers.core.FeathersControl.validateNow (feathers/core/FeathersControl.hx line 715)
: Called from feathers.core.ValidationQueue.validateNow (feathers/core/ValidationQueue.hx line 156)
: Called from feathers.core.ValidationQueue.validationQueue_stage_renderHandler (feathers/core/ValidationQueue.hx line 162)
: Called from openfl.events.EventDispatcher.__dispatchEvent (openfl/events/EventDispatcher.hx line 426)
: Called from openfl.display.DisplayObject.__dispatch (openfl/display/DisplayObject.hx line 1398)
: Called from openfl.display.Stage.__broadcastEvent (openfl/display/Stage.hx line 1187)
: Called from openfl.display.Stage.__render (openfl/display/Stage.hx line 2062)
: Called from openfl.display.Stage.__onLimeRender (openfl/display/Stage.hx line 2186)
: Called from lime.app._Event_lime_graphics_RenderContext_Void.dispatch (lime/_internal/macros/EventMacro.hx line 91)
: Called from lime._internal.backend.native.NativeApplication.handleRenderEvent (lime/_internal/backend/native/NativeApplication.hx line 375)
: Called from lime._internal.backend.native.NativeApplication.exec (lime/_internal/backend/native/NativeApplication.hx line 146)
: Called from lime.app.Application.exec (lime/app/Application.hx line 150)
: Called from openfl.display.Application.exec (openfl/display/Application.hx line 130)
: Called from ApplicationMain.create (ApplicationMain.hx line 142)
: Native : null
: Stack : null
: [2024-03-22 15:29:21][FATAL][Genesis/Source/genesis/application/GenesisApplication.hx:557] Fatal exception : [lime.utils.ObjectPool] ERROR: Object has already been released
: Details : Exception: [lime.utils.ObjectPool] ERROR: Object has already been released
: Called from lime.utils.Log.error (lime/utils/Log.hx line 37)
: Called from lime.utils.ObjectPool.release (lime/utils/ObjectPool.hx line 106)
: Called from openfl.text.TextField.__getBounds (openfl/text/TextField.hx line 1813)
: Called from openfl.display.DisplayObject.getBounds (openfl/display/DisplayObject.hx line 1184)
: Called from openfl.text.TextField.__updateScrollH (openfl/text/TextField.hx line 2304)
: Called from openfl.text.TextField.setSelection (openfl/text/TextField.hx line 1380)
: Called from openfl.text.TextField.__updateLayout (openfl/text/TextField.hx line 2264)
: Called from openfl.text.TextField.get_textWidth (openfl/text/TextField.hx line 3048)
: Called from feathers.controls.Label.refreshText (feathers/controls/Label.hx line 749)
: Called from feathers.controls.Label.update (feathers/controls/Label.hx line 583)
: Called from feathers.core.ValidatingSprite.validateNow (feathers/core/ValidatingSprite.hx line 289)
: Called from feathers.core.FeathersControl.validateNow (feathers/core/FeathersControl.hx line 715)
: Called from feathers.core.ValidationQueue.validateNow (feathers/core/ValidationQueue.hx line 156)
: Called from feathers.core.ValidationQueue.validationQueue_stage_renderHandler (feathers/core/ValidationQueue.hx line 162)
: Called from openfl.events.EventDispatcher.__dispatchEvent (openfl/events/EventDispatcher.hx line 426)
: Called from openfl.display.DisplayObject.__dispatch (openfl/display/DisplayObject.hx line 1398)
: Called from openfl.display.Stage.__broadcastEvent (openfl/display/Stage.hx line 1187)
: Called from openfl.display.Stage.__render (openfl/display/Stage.hx line 2062)
: Called from openfl.display.Stage.__onLimeRender (openfl/display/Stage.hx line 2186)
: Called from lime.app._Event_lime_graphics_RenderContext_Void.dispatch (lime/_internal/macros/EventMacro.hx line 91)
: Called from lime._internal.backend.native.NativeApplication.handleRenderEvent (lime/_internal/backend/native/NativeApplication.hx line 375)
: Called from lime._internal.backend.native.NativeApplication.exec (lime/_internal/backend/native/NativeApplication.hx line 146)
: Called from lime.app.Application.exec (lime/app/Application.hx line 150)
: Called from openfl.display.Application.exec (openfl/display/Application.hx line 130)
: Called from ApplicationMain.create (ApplicationMain.hx line 142)

[piotrzarzycki21]

I just catch that exception in Moonshine debugger. Here is screenshot. Maybe it helps you at some point:

I think stack var is null. Should I do something specific when I catch that again ?

@joshtynjala I got today exactly the same stacktrace. I'm using all your changes, feathers is updated to dev version and other libs as well.

[joshtynjala]

So far, I have been unable to reproduce any of the exceptions on my computer, and I can't think of anything else that I can try until we discover more clues. It is clear that this is related to the ObjectPool class in OpenFL, and I have tried various things to see if I could make an ObjectPool unexpectedly return null, but so far, I have been unsuccessful.

[piotrzarzycki21]

@joshtynjala I got today I believe connected to all of that crash. I took screenshot in Moonshine:

It looks like stack is null here.

[joshtynjala]

I think that I've finally figured out what is happening. You are using threads to do certain things in the background. And when the thread is done, or wants to indicate some kind of progress, it uses callbacks. The callbacks are used to update things in OpenFL and Feathers UI, but they're still running in the context of the background thread. OpenFL and Feathers UI APIs are meant to be used on the main thread only. You need to update how your thread handles callbacks so that the OpenFL and Feathers UI API calls are run in the context of the main thread instead.

I don't have a lot of experience working with Haxe's sys.thread.Thread directly. So I'm not sure if there's an easy way to do that. It may be possible to use MainLoop.runInMainThread() for the callbacks.

I recommend using BackgroundWorker from Lime because it has nice APIs for communicating things between the worker thread and the main thread. In OpenFL, we use BackgroundWorker in the File and FileStream classes for async APIs like copyToAsync().

https://github.com/openfl/openfl/blob/c457e2a/src/openfl/filesystem/File.hx#L979-L1017

The doWork event is where the code that runs in the worker thread should go. It is started by calling worker.run() in the main thread. worker.run() accepts an optional argument to safely pass objects from the main thread to the worker thread.

onComplete is called when sendComplete() is called from inside doWork. sendComplete() accepts an optional argument to safely pass objects back from the worker thread to the main thread.

onProgress is called when sendProgress() is called from inside doWork. sendProgress() accepts an optional argument to safely pass objects back from the worker thread to the main thread.

onError is called when sendError() is called from inside doWork.sendProgress() accepts an optional argument to safely pass objects back from the worker thread to the main thread.