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[6.2][clang][DependencyFile] Use atomic write for dependency file #10904

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[6.2][clang][DependencyFile] Use atomic write for dependency file #10904

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  • Explanation: Fix a race condition in the parallel build when dependency file is being updated by one compiler and being read by build system at same time. The fix is to make the write of .d file to be atomic.
  • Scope: Fix a race condition that can cause build failures occasionally.
  • Issues: rdar://154128578
  • Original PRs: [clang][DependencyFile] Use atomic write for dependency file #10902
  • Risk: Low. Change how the dependency file is written and no change in output content.
  • Testing: Unit Test
  • Reviewers: @benlangmuir

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[clang][DependencyFile] Use atomic write for dependency file (swiftla…
87a08f9 
…ng#10902)

Previously when switch to output backend, dependency file was relying
on non-atomic write + discard to remove the out of date dependency file
when there are missing headers. The reliance on non-atomic write can
cause race conditions that build system is trying to read the file while the
file is being updated by a different compiler instance.

rdar://154128578
@cachemeifyoucan cachemeifyoucan requested a review from a team as a code owner June 26, 2025 20:04
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@swift-ci please test

@cachemeifyoucan cachemeifyoucan requested a review from akyrtzi June 26, 2025 20:05
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@akyrtzi akyrtzi akyrtzi approved these changes

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