## Hello USD Users,
I'm currently working on an open-source USD Resolver and need some help refreshing a LOPs node stage. My primary goal is to reload all assets, which would be useful for clearing the resolver. In the future, I aim to implement functionality to reload specific assets selectively.
### The Problem
I assumed that running `.Reload()` on the stage provided by a node would cause the resolver to trigger `__RefreshContext()`, thereby refreshing the context and informing the stage that all resolves done with a given resolver are invalid. However, to my surprise, I encountered a *UseAfterFree* error.
I wasn’t able to dig too deeply into this with GDB, but I found that a series of locks were accessed by Houdini and one PXR lock (`pxrInternal_v0_24__pxrReserved__::XUSD_Data::afterLock`). This all occurred in a single thread within a combination of `libHoudiniUSD` and `libHoudiniAPPS3`. My assumption is that Houdini keeps the stage or layer pointer cached for later use, and when the resolver gets destructed, this leaves behind a dangling pointer.
### Issues Encountered
1. **Reloading USD Stage from Python LOP**: Attempting `.Reload()` on the stage not only fails but also causes a *use-after-free* error, resulting in segmentation faults.
2. **Resolver Context Notifications**:
- When I notify the stage that a resolver context has changed, all matching contexts are deleted. However, I don’t observe new resolutions.
- Based on the documentation, I assumed Houdini would reload everything since the notification invalidates the current resolver context, ensuring the user is shown up-to-date information.
3. **Re-resolution on Node Connection**:
- When connecting a new node, the entire stage is re-resolved, but this only occurs if something new is resolved.
- Is this behavior expected? I assumed the re-resolution would happen immediately after the stage is invalidated.
### Example Script
Here's a minimal script to reproduce the issue:
1. Go to LOPs.
2. Load something.
3. Run this in a Python LOP:
```python
node = hou.pwd()
stage = node.editableStage()
stage.Reload()
```
### Questions
1. Why does `.Reload()` fail and cause a segfault? Is it related to the stage being backed by an anonymous `SdfLayer`?
2. What is the expected behavior of the resolver context notification? Shouldn’t it trigger a reload automatically?
3. Is it normal for the stage to be re-resolved only when a new asset is resolved, rather than immediately after invalidation?
Any insights or suggestions to address these issues would be greatly appreciated!
Thanks in advance for your help!
Reloading USD Stages Causes UseAfterFree Error
103 0 1- lyon001
- Member
- 3 posts
- Joined: 5月 2019
- Offline
-
- Quick Links