Bug with MergingSceneIndex handling of prim removal

marktucker commented 2 weeks ago

Description of Issue

There is a problem with how the HdMerginsSceneIndex handles _PrimsRemoved which can lead to hydra accessing invalid/expired UsdPrim objects, which results in exceptions being thrown and a failed hydra sync.

Steps to Reproduce

Expand the attached zip file and open usdview on output0.usda, with USDIMAGINGGL_ENGINE_ENABLE_SCENE_INDEX=1. prim_removal.zip
In the interpreter window, run the following code. This will cause usdview to show a grid of instanced cubes. All good.
```
l = usdviewApi.stage.GetRootLayer()
with Sdf.ChangeBlock():
l.subLayerPaths = ['F:/hips/139418/output1.usda']
```
In the interpreter window, run the following code. This should delete the point instancer and replace it with a single cube. But the update process throws an exception.
```
with Sdf.ChangeBlock():
l.subLayerPaths = ['F:/hips/139418/output2.usda']
```

The exception I see in the console is:

ERROR: Usdview encountered an error while rendering.Used expired 'Cube' prim </i
nstancer1/Prototypes/things/cube>  - UsdExpiredPrimAccessError thrown:
-> Usd_ThrowExpiredPrimAccessError at F:\dev_tools\src\usd\usd-24.08\USD-py3.11
-qt5\pxr\usd\usd\primData.cpp:266 from
 #0   0x00000000c351a44c in Tf_Throw<UsdExpiredPrimAccessError,basic_string<
char,char_traits<char>,allocator<char> > >+0xcc
 #1   0x00000000c351a373 in Tf_Throw<UsdExpiredPrimAccessError,basic_string<
char,char_traits<char>,allocator<char> > >+0x43
 #2   0x00000000c3517e68 in Usd_ThrowExpiredPrimAccessError+0x118
 #3   0x00000000cc0d0e10 in Usd_PrimDataHandle::operator->+0x40
 #4   0x00000000cc3554bc in UsdPrim::IsInstance+0x1c
 #5   0x00000000cc354eb5 in UsdImagingDataSourceUsdPrimInfo::Get+0x175
 #6   0x00000000cc5c01a2 in `anonymous namespace'::_RerootingSceneIndexConta
inerDataSource::Get+0xd2
 #7   0x00000000cc278bc0 in HdSchema::_GetTypedDataSource<HdTypedSampledData
Source<SdfPath> >+0x80
 #8   0x00000000cc597097 in UsdImagingUsdPrimInfoSchema::GetNiPrototypePath+
0x57
 #9   0x00000000cc4046bf in `anonymous namespace'::_IsUsdNativeInstance+0x4f
 #10  0x00000000cc404855 in `anonymous namespace'::_GetDrawMode+0x95
 #11  0x00000000cc403823 in UsdImagingDrawModeSceneIndex::_PrimsDirtied+0x44
3
 #12  0x00000000c246fbea in HdSingleInputFilteringSceneIndexBase::_Observer:
:PrimsDirtied+0x4a
 #13  0x00000000c26f8282 in HdSceneIndexBase::_SendPrimsDirtied+0x102
 #14  0x00000000c2485d2c in HdFlatteningSceneIndex::_PrimsAdded+0x26c
 #15  0x00000000c246fb2a in HdSingleInputFilteringSceneIndexBase::_Observer:
:PrimsAdded+0x4a
... 40 more frames

System Information (OS, Hardware)

Windows

Package Versions

USD 24.08

Lumengine commented 1 week ago

Hi, I also encountered this errorwith my custom implementation. Crash appeared when repopulate subtree with another stage.

jesschimein commented 1 week ago

Filed as internal issue #USD-10052

PixarAnimationStudios / OpenUSD