[llvm][cas] Fix thread safety issues with MappedFileRegionBumpPtr #8621
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@swift-ci please test llvm |
cachemeifyoucan
approved these changes
Apr 22, 2024
| #include <thread> | ||
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| #if __has_include(<sys/file.h>) | ||
| #include <sys/file.h> |
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Is this a common unix header or is this macOS only?
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It's the same on Linux https://man7.org/linux/man-pages/man2/flock.2.html
| @@ -52,12 +52,14 @@ | |||
| //===----------------------------------------------------------------------===// | |||
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| #include "llvm/CAS/MappedFileRegionBumpPtr.h" | |||
| #include "llvm/ADT/ScopeExit.h" | |||
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don't need empty line around this include?
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Hmm, I see a mix of styles for including lib-directory headers. Some have empty lines around it, some only have empty line above it, some have no empty lines. Not clear to me what it should be
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No spaces seems more common, going with that.
llvm::sys::fs::lockFile and friends, which are implemented with fcntl F_SETLK, are only safe to use across processes and not across threads. We were attempting to workaround that using createShared, which tries to unique the mapped file per process, but (a) that only works if you have a single copy of llvm in your process, which may not always be true, and (b) we had a race in the implementation between closing one CAS and opening a new one at the same path. Replace these with an flock-based implementation. Since this is not available on all platforms LLVM supports we use a separate implementation for the on-disk CAS rather than change llvm::sys::fs::lockFile. rdar://126882843
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llvm::sys::fs::lockFileand friends, which are implemented withfcntl F_SETLK, are only safe to use across processes and not across threads. We were attempting to workaround that usingcreateShared, which tries to unique the mapped file per process, but (a) that only works if you have a single copy of llvm in your process, which may not always be true, and (b) we had a race in the implementation between closing one CAS and opening a new one at the same path. Replace these with an flock-based implementation. Since this is not available on all platforms LLVM supports we use a separate implementation for the on-disk CAS rather than change llvm::sys::fs::lockFile.rdar://126882843