[5.4][Runtime] Fix race condition in protocol conformance lookups that caused false negatives. #35850
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…sed false negatives. In the uncached case, we'd scan conformances, cache them, then re-query the cache. This worked fine when the cache always grew, but now we clear the cache when loading new Swift images into the process. If that happens between the scan and the re-query, we lose the entry and return a false negative. Instead, track what we've found in the scan in a separate local table, then query that after completing the scan. While we're in there, fix a bug in TypeLookupError where operator= accidentally copied this->Context instead of other.Context. This caused the runtime to crash when trying to print error messages due to the false negative. Add a no-parameter constructor to TypeLookupErrorOr<> to distinguish the case where it's being initialized with nothing from the case where it's being initialized with nullptr. rdar://72865822 (cherry picked from commit 3a2ea08)
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@swift-ci please test |
grynspan
reviewed
Feb 9, 2021
| if (!found.first) | ||
| C.cacheResult(type, protocol, found.second, snapshot.count()); | ||
| // If there's no entry here, move up to the superclass (if any). | ||
| if (!foundWitness) |
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I believe this test will fail to distinguish between "value not found" and "NULL found".
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Oh, C is not the same as foundWitnesses. foundWitnesses is local. It's a local variable. It's a variable that's only used locally.
tkremenek
approved these changes
Feb 9, 2021
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Cherry-pick of #35836 to 5.4 branch.
In the uncached case, we'd scan conformances, cache them, then re-query the cache. This worked fine when the cache always grew, but now we clear the cache when loading new Swift images into the process. If that happens between the scan and the re-query, we lose the entry and return a false negative.
Instead, track what we've found in the scan in a separate local table, then query that after completing the scan.
While we're in there, fix a bug in TypeLookupError where operator= accidentally copied this->Context instead of other.Context. This caused the runtime to crash when trying to print error messages due to the false negative.
Add a no-parameter constructor to TypeLookupErrorOr<> to distinguish the case where it's being initialized with nothing from the case where it's being initialized with nullptr.
rdar://72865822