Try once again to fix the element already registered bug #290795
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Pull request overview
This PR fixes a race condition bug in tree view handling where concurrent getChildren calls could result in "Element with id ... is already registered" errors. The bug occurred when _childrenFetchTokens was cleared during a root refresh, causing multiple in-flight fetches to reset their request IDs and potentially conflict when registering elements.
Changes:
- Introduced a global monotonically increasing counter (
_globalFetchTokenCounter) to replace per-element request ID tracking - Added a comprehensive test case that reproduces the race condition scenario with concurrent reveal operations returning different element instances with the same ID
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/vs/workbench/api/common/extHostTreeViews.ts | Added global fetch token counter and modified _fetchChildrenNodes to use it instead of per-element counters, ensuring old in-flight fetches never match new fetches after cache clears |
| extensions/vscode-api-tests/src/singlefolder-tests/tree.test.ts | Added regression test that reproduces the race condition with two concurrent reveal operations returning different element instances with the same ID |
bpasero
approved these changes
Jan 27, 2026
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Fixes microsoft/vscode-pull-request-github#8073