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bpy.types.SpaceView3D.draw_handler_remove(...) causes Blender to crash
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System Information
Operating system: Linux-5.4.0-66-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 450.102.04

Blender Version
Broken: version: 2.92.0, branch: master, commit date: 2021-02-24 16:25, hash: rB02948a2cab44
Worked: never

Short description of error
Using bpy.types.SpaceView3D.draw_handler_remove(...) causes Blender to crash.

Exact steps for others to reproduce the error

  1. Open the attached script in the script editor
  2. Uncomment line 80-82
  3. Run the script
  4. Delete the empty named "anchor"
ED_region_draw_cb_draw(const bContext * C, ARegion * region, int type) Line 266	C
DRW_draw_callbacks_post_scene() Line 1439	C
DRW_draw_render_loop_ex(Depsgraph * depsgraph, RenderEngineType * engine_type, ARegion * region, View3D * v3d, GPUViewport * viewport, const bContext * evil_C) Line 1646	C
DRW_draw_view(const bContext * C) Line 1514	C
view3d_draw_view(const bContext * C, ARegion * region) Line 1607	C
view3d_main_region_draw(const bContext * C, ARegion * region) Line 1630	C
ED_region_do_draw(bContext * C, ARegion * region) Line 563	C
wm_draw_window_offscreen(bContext * C, wmWindow * win, bool stereo) Line 732	C
wm_draw_window(bContext * C, wmWindow * win) Line 875	C
wm_draw_update(bContext * C) Line 1074	C
WM_main(bContext * C) Line 644	C
main(int argc, const unsigned char * * UNUSED_argv_c) Line 526	C

Original description:
Please execute the python script below.

The script uses bpy.types.SpaceView3D.draw_handler_add()to add a call back function that draws a simple point cloud.
The drawing of the point cloud depends on an empty object named anchor.
If the user deletes this object, the point cloud is no longer drawn (and the call back should be removed with bpy.types.SpaceView3D.draw_handler_remove(...)).
Currently, bpy.types.SpaceView3D.draw_handler_remove(...) is commented out to show this behavior.
When uncommenting bpy.types.SpaceView3D.draw_handler_remove(...) (see line 80) to remove the callback, Blender crashes.

The corresponding error message of /tmp/blender.crash.txt can be found in the following file:

Event Timeline

Robert Guetzkow (rjg) changed the task status from Needs Triage to Confirmed.Feb 28 2021, 11:25 PM

I'm marking this as confirmed, but given the reference passing of an object that is no longer valid at a later point in time this might be an unsupported use case / a limitation by the Python API (see the Gotchas of the Python API, especially about storing references to objects). However, I believe this is a bug since removing the handler should not be causing the problem, but someone more familiar with the design of the draw handler should take a look at this.

Thank you for having a look at this.
I also thought about this. This is why I tried to keep a reference with

bpy.types.Object.current_draw_manager = draw_callback_handler

that allows to access the draw_callback_handler after the script terminated.
Even with the line above, the example script kept crashing. (However, I'm unsure if bpy.types.Object.current_draw_manager = draw_callback_handler achieves the intended effect.)

@Germano Cavalcante (mano-wii) Thank you for looking into this. Indeed the callback itself removes handler, causing the issue you've identified.