Windows: Faster getenvW
and a standalone environment variable test
#23272
+170
−14
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Outdated suggestions cannot be applied.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.
Inspired by #23265, I thought I'd try applying the same strategy to the Windows implementation. Also adds a standalone test to make sure the functionality remains the same.
Instead of parsing the full key and value for each environment variable before checking the key for (case-insensitive) equality, we skip to the next environment variable once it's no longer possible for the key to match.
This makes getting environment variables about 2x faster across the board on Windows.
Note: We still have to scan to find the end of each environment variable (even the ones that are skipped, since we only know where it ends by a NUL terminator), so this strategy doesn't provide the same speedup on Windows as it does on POSIX (#23265)
Benchmark code
(presumably, the magnitude of any speedup would also (on average) increase as the number of environment variables in the environment increases)