[POSIX] Use flock instead of fcntl#973
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AlCutter
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Jun 2, 2026
AlCutter
approved these changes
Jun 2, 2026
BSD flock locks are associated with the open file description rather than the PID, which prevents different file descriptors in the same process from concurrently acquiring the lock. This avoids a silent-release vulnerability where closing any file descriptor to the lock file in the process immediately drops the lock for all other descriptors. This doesn't fix any immediate known issues. However, it does make things less brittle. Should we change which files are written from different goroutines in the future, this will protect against multiple workers ignoring each other's locks. It also avoids a risk that a library user could create 2 instances of a POSIX storage backed by the same directory. Previously these would have ignored each other's locks, but now they will respect them.
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BSD flock locks are associated with the open file description rather than the PID, which prevents different file descriptors in the same process from concurrently acquiring the lock. This avoids a silent-release vulnerability where closing any file descriptor to the lock file in the process immediately drops the lock for all other descriptors.
This doesn't fix any immediate known issues. However, it does make things less brittle. Should we change which files are written from different goroutines in the future, this will protect against multiple workers ignoring each other's locks.
It also avoids a risk that a library user could create 2 instances of a POSIX storage backed by the same directory. Previously these would have ignored each other's locks, but now they will respect them.