Fix race condition in SharedMemoryHelpers.CreateOrOpenFile for named mutexes on Unix#129923
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Fix race condition in SharedMemoryHelpers.CreateOrOpenFile for named mutexes on Unix#129923Copilot wants to merge 8 commits into
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When O_CREAT|O_EXCL fails with EEXIST, another process created the file between our ENOENT check and our creation attempt. Instead of throwing an IOException, retry opening the existing file from the top of the loop. This fixes the race condition that caused: System.IO.IOException: The file '...NuGet-Migrations' already exists. when two processes try to create the same named mutex simultaneously. Closes #91987 Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
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[WIP] Fix issue with opening device or file specified 'NuGet-Migrations'
Fix race condition in SharedMemoryHelpers.CreateOrOpenFile for named mutexes on Unix
Jun 27, 2026
This was referenced Jun 27, 2026
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Pull request overview
This PR updates the Unix shared-memory file open/create path used by named mutexes to be resilient to cross-process creation races, by retrying when the exclusive create attempt fails with EEXIST.
Changes:
- Wrap
SharedMemoryHelpers.CreateOrOpenFilein a retry loop. - When
O_CREAT|O_EXCLfails withEEXIST, retry by opening the now-existing file instead of throwing.
jkotas
reviewed
Jun 27, 2026
jkotas
reviewed
Jun 27, 2026
jkotas
reviewed
Jun 27, 2026
Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
jkotas
reviewed
Jun 27, 2026
This was referenced Jun 27, 2026
Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
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Two processes racing to create the same named mutex could hit a TOCTOU window where
O_RDWRsees ENOENT butO_CREAT|O_EXCLthen fails with EEXIST (another process won the race), producing an unhandledIOException.This mirrors the existing retry pattern already used in
EnsureDirectoryExistsfor the same class of race.