refactor: revise server architecture #1884
Merged
Conversation
This file contains 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
Replace complex debouncing logic in watchdog with single `IO.sleep` in worker `didChange` handler, replace redundant header change logic in watchdog with special exit code from worker.
github-merge-queue bot
pushed a commit
that referenced
this pull request
Aug 7, 2024
This PR resolves two language server bugs that especially affect Windows users: 1. Editing the header could result in the watchdog not correctly restarting the file worker (#3786, #3787), which would lead to the file seemingly being processed forever. - The cause of this issue was a race condition in the watchdog that was accidentally introduced as far back as #1884: In specific circumstances, the watchdog will attempt forwarding a message to the file worker after the process has exited due to a changed header, but before the file worker exiting has been noticed by the watchdog (which will then restart the file worker). In this case, the watchdog would mark the file worker as having crashed and not look at its exit code to restart the file worker, but instead treat it like a crashed file worker that will only be restarted when editing the file again. Not inspecting the exit code of the file worker when it crashed from forwarding a message from the file worker is necessary since we do not restart the file worker until another notification from the client arrives, and so we would read the same crash exit code over and over again in the main loop of the watchdog if we did not remove it from our list of file workers that we listen to. - This PR resolves this issue by distinguishing between "crashes when forwarding messages to the file worker" and "crashes when forwarding messages from the file worker". In the former case, we still inspect the exit code of the file worker and potentially restart it if the imports changed, whereas in the latter case, we stop inspecting the exit code of the file worker. This is correct because the latter case is exactly the one where we need to stop inspecting the exit code but where a crash cannot occur as a result of a changed header, whereas the former case is exactly the one where we still need to inspect the exit code after a crash to ensure that we restart the file worker in case it exited because the header changed. - At some point in the future, it would be nice to revamp the concurrency model of the watchdog entirely now that we have all those fancy concurrency primitives that were not available four years ago when the watchdog was first written. 2. On an especially slow Windows machine, we found that starting the language server would sometimes not succeed at all because reading from the stdin pipe in the watchdog produced an EINVAL error, which was in turn caused by an NT "pipe empty" error. - After lots of debugging, @Kha found that Lake accidentally passes its stdin to Git because it does not explicitly set the `stdin` field to `null` when spawning the process. - Changing this fixes the issue, which suggests that Git may mutate the pipe we pass to it to be non-blocking, which then causes a "pipe empty" error in the watchdog when we also attempt to read from that same pipe. - I'm still very uncertain why we only saw this issue on one particularly slow machine and not across the whole eco system. This PR also resolves an issue where we would not correctly emit messages that we received while the file worker is being restarted to the corresponding file worker after the restart. Closes #3786, closes #3787. --------- Co-authored-by: Sebastian Ullrich <sebasti@nullri.ch>
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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.
Replace complex debouncing logic in watchdog with simple
IO.sleepin workerdidChangehandler, replace redundant header change logic in watchdog with special exit code from worker.This should not yet introduce noticeable changes in behavior, but apart from drastically simplifying the code, it does open up future opportunities such as not restarting the worker until the new header is actually valid, which might help with implementing import completion.