Fix ABBA deadlock between waitForTransform and testTransformableRequests (backport #982) - #987
Open
mergify[bot] wants to merge 1 commit into
Open
Fix ABBA deadlock between waitForTransform and testTransformableRequests (backport #982)#987mergify[bot] wants to merge 1 commit into
waitForTransform and testTransformableRequests (backport #982)#987mergify[bot] wants to merge 1 commit into
Conversation
ahcorde
approved these changes
Sep 7, 2026
Contributor
|
Pulls: #987
|
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Description
As mentioned in #979, an ABBA deadlock situation was introduced in #966 where
testTransformableRequests()lockstransformable_requests_mutex_and tries to run cb which requirestimer_to_request_map_mutex_while parallelywaitForTransformacquirestimer_to_request_map_mutex_and tries to calladdTransformableRequestwhich internally needstransformable_requests_mutex_resulting in ABBA situation.My apologies for not noticing this issue previously and a special thanks to @jplapp and @mini-1235 for bringing it to my attention.
@mini-1235 has already opened #979 to fix this issue. I agree with the approach in that PR (to unlock mutex before running callbacks and lock again) but I think restarting the
iand going through the beginning of the requests for every callback would add unnecessary computation time. More precisely, the cost is that if M callbacks fire persetTransformand N requests are pending, you get O(M·N) work instead of O(N).I tried to improve that by going through the requests first, extracting the pending callbacks and then running them. That way we keep the swap-and-pop behavior as before.
I have also copied the test @jplapp added in #980 here as well. @mini-1235 could you please also check this in your nav2 setup where this problem became highlighted?
Credits to @jplap and @mini-1235 for their idea and suggested changes.
Did you use Generative AI?
Yes, Claude Sonned 4.6
This is an automatic backport of pull request #982 done by [Mergify](https://mergify.com).