Module lock_file 

Exclusive lock files whose body names the holder.

The session journal lock and the keeper locks write the holder’s identity into the locked file, so a process that is refused can say who has it. On Unix the lock is an advisory flock, which never blocks a read. Windows byte-range locks are mandatory: fs4 (like File::try_lock) locks the whole file from offset 0, so the refused process could not read the body and every refusal lost its holder (“held by another process”). There the lock covers one byte far past any body instead. That byte lies inside the whole-file range, so it still excludes, and is excluded by, a binary that locks the whole file.

A lock is released by dropping its ExclusiveLock, which unlocks explicitly before the file closes. Closing alone is not enough: a flock belongs to the open file description, and a child forked by any thread of this process holds a copy of every descriptor until it execs (O_CLOEXEC applies only at exec). Until then the lock would outlive its owner, and an immediate re-lock be refused in the name of this very process. Windows releases a closed handle’s locks only “depending on available system resources”, so there an explicit unlock is what makes the release prompt.

Structs

ExclusiveLock

An exclusive lock on a file, released when dropped.

Functions

try_lock

Take the exclusive lock on file without waiting: Ok(None) if another handle holds it.