Repository navigation
Optimize Iterator for IIterator<T> - #3476
Merged
Merged
Conversation
Comment on lines
+464
to
+468
| let result = if self.HasCurrent().unwrap_or(false) { | ||
| self.Current().ok() | ||
| } else { | ||
| None | ||
| }; |
Collaborator
Author
There was a problem hiding this comment.
This is the only change - the rest are the output of code generation used for validation.
Eugene (talagrand)
approved these changes
Feb 6, 2025
|
Nice! |
James McNellis (JamesMcNellis)
approved these changes
Feb 7, 2025
Collaborator
|
lgtm |
Merged
Member
|
2 calls is not a problem for in process APIs. but for out of process APIs, the cost per call is very high. |
Collaborator
Author
|
Yes, in pathological cases you'd want to use |
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
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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
C++/WinRT uses exceptions for error propagation and unfortunately exceptions continue to be very slow. I hadn't realized how much slower until a customer shared some logs. I decided to take a fresh look and compare the Rust implementation of
IIterator<T>::CurrentreturningE_BOUNDSto C++/WinRT's implementation that throws before returningE_BOUNDS. For a million calls:RoOriginate): 3.95sSo that's quite a difference. Ideally we can get C++/WinRT to avoid exceptions but this probably merits a tweak in Rust to avoid this pathological case as changing C++ is hard.
This change tweaks the
Iteratortrait implementation on the Rust side to useHasCurrentto avoid calls toCurrentand thus avoid those exceptions. With this change, the cost of iteration for C++ implementations approaches that of Rust.Thanks to James McNellis (@JamesMcNellis) for prodding me to look into this a bit more closely. He also gave a great talk on how exceptions work that you should definitely check out.