map_reduce: prevent mapper exception from poisoning state #2684
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
In map_reduce, if the mapper throws, we can end up with poisoned state. This is because the compiler can choose to move s->result before evaluating f.get(), so s->result gets broken (if the mapped type becomes invalid after move). Fix by triggering the exception before the moving s->result, with a sequence point to force the ordering. A unit test is added (which does fail with clang before the patch, though if the arguments are evaluated in reverse order, it can pass with a different compiler).
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Outdated suggestions cannot be applied.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.
In map_reduce, if the mapper throws, we can end up with poisoned state. This is because the compiler can choose to move s->result before evaluating f.get(), so s->result gets broken (if the mapped type becomes invalid after move).
Fix by triggering the exception before the moving s->result, with a sequence point to force the ordering.
A unit test is added (which does fail with clang before the patch, though if the arguments are evaluated in reverse order, it can pass with a different compiler).