Crash when appending object using callack from enum prop, followed by undo #82361

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MACHIN3 · 2020-11-03T13:46:18+01:00

MACHIN3 commented

2020-11-03 13:46:18 +01:00

System Information
Operating system: Linux-4.15.0-117-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 1050/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21

Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: 3e85bb34d0
Worked: 2.82

Short description of error
This is a follow-up to https://developer.blender.org/T80217

I'm using the update callback of an enum prop to append an object from an external blend file, then link it to the master collection.
This is a fairly standard procedure for addons using layout.template_icon_view() to "load assets".

In the previous report, it was suggested to not call an operator from the update callback to prevent crashes, if the user were to undo after such an "asset load".

This new report then avoids using an operator and instead uses a dedicated append_object_function().
Unfortunately the crash is still happening as soon as one does an undo.

As in the previous report, appending using layout.operator() works fine. All of this worked up until 2.82 and 2.83 was the first to crash.

If the suggestion now is to not do any database manipulation from update callbacks, then what is the recommended way to bring in external assets using template icon views? If this isn't possible anymore, than it seems this layout element is a lot less useful, and addons that have been building on this ability for years are now a serious cause of blender instability and potential for data loss.

append_obj_undo_crash_from_update_callback_of_enum_prop.zip

Exact steps for others to reproduce the error

Extract the above zip file and open append_obj_undo_crash_from_template_icon_view.blend
Run the script
In the 3d view sidebar, a new panel 'Append Object' appears under the Tool tab
In the Append Object panel, click on the thumbnail, and again on the blender icon inside
- the append object op was called and a cube was appended to the scene
Undo
- Blender should crash!!!
Start Blender again and run the script again
This time, run the append op using the button below the thumbnail, then undo again
- Blender should not crash this time

**System Information** Operating system: Linux-4.15.0-117-generic-x86_64-with-debian-buster-sid 64 Bits Graphics card: GeForce GTX 1050/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21 **Blender Version** Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: `3e85bb34d0` Worked: 2.82 **Short description of error** This is a follow-up to https://developer.blender.org/T80217 I'm using the update callback of an enum prop to append an object from an external blend file, then link it to the master collection. This is a fairly standard procedure for addons using `layout.template_icon_view()` to "load assets". In the previous report, it was suggested to not call an operator from the update callback to prevent crashes, if the user were to undo after such an "asset load". This new report then avoids using an operator and instead uses a dedicated `append_object_function()`. Unfortunately the crash is still happening as soon as one does an undo. As in the previous report, appending using `layout.operator()` works fine. All of this worked up until 2.82 and 2.83 was the first to crash. If the suggestion now is to not do any database manipulation from update callbacks, then what is the recommended way to bring in external assets using template icon views? If this isn't possible anymore, than it seems this layout element is a lot less useful, and addons that have been building on this ability for years are now a serious cause of blender instability and potential for data loss. [append_obj_undo_crash_from_update_callback_of_enum_prop.zip](https://archive.blender.org/developer/F9180709/append_obj_undo_crash_from_update_callback_of_enum_prop.zip) **Exact steps for others to reproduce the error** * Extract the above zip file and open append_obj_undo_crash_from_template_icon_view.blend * Run the script * In the 3d view sidebar, a new panel 'Append Object' appears under the Tool tab * In the Append Object panel, click on the thumbnail, and again on the blender icon inside * the append object op was called and a cube was appended to the scene * Undo * Blender should crash!!! * Start Blender again and run the script again * This time, run the append op using the button below the thumbnail, then undo again * Blender should not crash this time

MACHIN3 commented

2020-11-03 13:46:18 +01:00

Added subscriber: @MACHIN3

Bastien Montagne was assigned by MACHIN3

2020-11-03 13:46:48 +01:00

Philipp Oeser commented

2020-11-03 14:24:56 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-11-03 14:24:56 +01:00

Please read through #81345 (ID user decrement error when removing object which is referred to with a PointerProperty) starting:

In #81345#1027338, @mont29 wrote:
... note that manipulating data-blocks from update callback as you do in your script is extremely discouraged, it will basically break undo/redo process, among other potential severe issues, see the API documentation .

Please read through #81345 (ID user decrement error when removing object which is referred to with a PointerProperty) starting: > In #81345#1027338, @mont29 wrote: > ... note that manipulating data-blocks from `update` callback as you do in your script is extremely discouraged, it will basically break undo/redo process, among other potential severe issues, see [the API documentation](https://docs.blender.org/api/master/info_gotcha.html#abusing-rna-property-callbacks) .

Piotr commented

2020-11-03 16:31:23 +01:00

Added subscriber: @Pinnhead

Piotr commented

2020-11-03 16:31:23 +01:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.09

Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: 3e85bb34d0

Exactly the same behaviour.

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.09 **Blender Version** Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: `3e85bb34d0` Exactly the same behaviour.

Bastien Montagne commented

2020-11-03 16:50:12 +01:00

Changed status from 'Needs Triage' to: 'Archived'

Bastien Montagne closed this issue

2020-11-03 16:50:12 +01:00

Bastien Montagne commented

2020-11-03 16:50:12 +01:00

In #82361#1047115, @lichtwerk wrote:
Please read through #81345 (ID user decrement error when removing object which is referred to with a PointerProperty) starting:

In #81345#1027338, @mont29 wrote:
... note that manipulating data-blocks from update callback as you do in your script is extremely discouraged, it will basically break undo/redo process, among other potential severe issues, see the API documentation .

Nuf said.

> In #82361#1047115, @lichtwerk wrote: > Please read through #81345 (ID user decrement error when removing object which is referred to with a PointerProperty) starting: > >> In #81345#1027338, @mont29 wrote: >> ... note that manipulating data-blocks from `update` callback as you do in your script is extremely discouraged, it will basically break undo/redo process, among other potential severe issues, see [the API documentation](https://docs.blender.org/api/master/info_gotcha.html#abusing-rna-property-callbacks) . Nuf said.

MACHIN3 commented

2020-11-03 18:45:13 +01:00

Read all of this, still don't have a working solution to prevent Blender crashing when appending using the layout.template_icon_view() as the interface (followed by undo)

Don't use an operator in update callbacks
Use an operator when manipulating the database
So, there's a problem now.

I've tried calling the op from a timer and it's still crashing, will report that separately.

To me this looks like it should be something that is supported by the API. It's a massively popular use case, and shouldn't crash.

Read all of this, still don't have a working solution to prevent Blender crashing when appending using the `layout.template_icon_view()` as the interface (followed by undo) 1. Don't use an operator in update callbacks 2. Use an operator when manipulating the database So, there's a problem now. I've tried calling the op from a timer and it's still crashing, will report that separately. To me this looks like it should be something that is supported by the API. It's a massively popular use case, and shouldn't crash.

Pauan commented

2020-11-03 19:01:27 +01:00

Added subscriber: @pauanyu_blender

Philipp Oeser commented

2020-11-05 09:17:57 +01:00

I guess you need a separate operator [not called by a timer] that you need to execute "by hand".
So you choose your icon, then execute the operator (e.g. by button).

Not the nicest thing in the world, but a compromise.

I guess you need a separate operator [not called by a timer] that you need to execute "by hand". So you choose your icon, then execute the operator (e.g. by button). Not the nicest thing in the world, but a compromise.

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Crash when appending object using callack from enum prop, followed by undo #82361