Calling operator from handler that saves bmesh freezes blender forever #108865

New Issue

Andrej · 2023-06-11T20:35:01+02:00

Andrej commented

2023-06-11 20:35:01 +02:00

Blender version: 3.5.1

I setup some shader to run on top of blender viewport and connected it’s update to SpaceView3D.draw_handler_add. The idea was that shader will only work in EDIT mode and if user exists it then it will automatically trigger some operator.
Line that freezes Blender is bm.to_mesh(context.object.data) although it doens’t freeze right away.

What I’ve found that if I call operator that edits mesh from bmesh then it freezes Blender entirely.
Currently as a workaround I moved operator’s code to some function and call it instead of because bm.to_mesh(context.object.data) doesn’t seem to freeze Blender when it’s called from handler without operator.

Easy way to reproduce (create default scene, make sure cube is selected, run the script):

import bpy
from bpy.types import SpaceView3D
import bmesh

class TestHandler:
    installed = None

    @classmethod
    def install(cls, context):
        handler = cls()
        cls.installed = SpaceView3D.draw_handler_add(
            handler, (context, ), "WINDOW", "POST_VIEW"
        )

    @classmethod
    def uninstall(cls):
        try:
            SpaceView3D.draw_handler_remove(cls.installed, "WINDOW")
        except ValueError:
            pass
        cls.installed = None

    def __call__(self, context):
        obj = context.object
        if obj.mode != "EDIT":
            TestHandler.uninstall()
            bpy.ops.test.test()
            print('HANDLER CALL FINISHED') # never printed
            return
        
        print('HANDLER FINISHED')

class TestOperator(bpy.types.Operator):
    bl_idname = "test.test"
    bl_label = "test"

    def execute(self, context):
        print('TEST OPERATOR CALLED')
        bm = bmesh.new()

        # WITHOUT THIS LINE IT DOESN'T FREEZE
        bm.to_mesh(context.object.data)

        # still printed
        print('TEST OPERATOR FINISHED')
        return {"FINISHED"}
    
class TestSetupOperator(bpy.types.Operator):
    bl_idname = "test.test_setup"
    bl_label = "test"

    def execute(self, context):
        print('TEST SETUP OPERATOR CALLED')
        TestHandler.install(context)
        return {"FINISHED"}


bpy.utils.register_class(TestOperator)
bpy.utils.register_class(TestSetupOperator)
bpy.ops.object.mode_set(mode="EDIT")
bpy.ops.test.test_setup()
# freezes on the next step
bpy.ops.object.mode_set(mode="OBJECT")

Blender version: 3.5.1 I setup some shader to run on top of blender viewport and connected it’s update to `SpaceView3D.draw_handler_add`. The idea was that shader will only work in EDIT mode and if user exists it then it will automatically trigger some operator. Line that freezes Blender is `bm.to_mesh(context.object.data)` although it doens’t freeze right away. What I’ve found that if I call operator that edits mesh from bmesh then it freezes Blender entirely. Currently as a workaround I moved operator’s code to some function and call it instead of because `bm.to_mesh(context.object.data)` doesn’t seem to freeze Blender when it’s called from handler without operator. Easy way to reproduce (create default scene, make sure cube is selected, run the script): ```python import bpy from bpy.types import SpaceView3D import bmesh class TestHandler: installed = None @classmethod def install(cls, context): handler = cls() cls.installed = SpaceView3D.draw_handler_add( handler, (context, ), "WINDOW", "POST_VIEW" ) @classmethod def uninstall(cls): try: SpaceView3D.draw_handler_remove(cls.installed, "WINDOW") except ValueError: pass cls.installed = None def __call__(self, context): obj = context.object if obj.mode != "EDIT": TestHandler.uninstall() bpy.ops.test.test() print('HANDLER CALL FINISHED') # never printed return print('HANDLER FINISHED') class TestOperator(bpy.types.Operator): bl_idname = "test.test" bl_label = "test" def execute(self, context): print('TEST OPERATOR CALLED') bm = bmesh.new() # WITHOUT THIS LINE IT DOESN'T FREEZE bm.to_mesh(context.object.data) # still printed print('TEST OPERATOR FINISHED') return {"FINISHED"} class TestSetupOperator(bpy.types.Operator): bl_idname = "test.test_setup" bl_label = "test" def execute(self, context): print('TEST SETUP OPERATOR CALLED') TestHandler.install(context) return {"FINISHED"} bpy.utils.register_class(TestOperator) bpy.utils.register_class(TestSetupOperator) bpy.ops.object.mode_set(mode="EDIT") bpy.ops.test.test_setup() # freezes on the next step bpy.ops.object.mode_set(mode="OBJECT") ```

Andrej added the

labels 2023-06-11 20:35:02 +02:00

YimingWu commented

2023-06-12 05:49:02 +02:00

It's probably not expected to call operator "POST_VIEW", since it will always be called when there's a viewport update, but need more investigation.

When Blender is frozen, the CPU usage here shows zero so it might not be a stuck loop, looks more likely a dead lock situation.

For now try not to call operator within a handler, will poke developers about this.

It's probably not expected to call operator "POST_VIEW", since it will always be called when there's a viewport update, but need more investigation. When Blender is frozen, the CPU usage here shows zero so it might not be a stuck loop, looks more likely a dead lock situation. For now try not to call operator within a handler, will poke developers about this.

YimingWu added the

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Calling operator from handler that saves bmesh freezes blender forever #108865