Module resource_lock

Re-entrant lock manager that prevents multiple threads or processes from concurrently holding a lock on the same resource. I’m using it to mimic transactions in a database, but it could be used for other things too. It’s LLM generated and I don’t really understand all of it. Works on a best-effort basis; it’s likely to be flaky on network filesystems, FUSE, non-POSIX OSes, etc.

Guarantees, in principle:

• Mutual exclusion across threads for a given (resource_type, id).
• Re-entrant acquisition by the SAME thread won’t deadlock (recursion counter).
• OS-level advisory file lock held exactly once while any logical acquisitions exist.
• Other threads attempting acquisition block until the owning thread fully releases (recursion -> 0).

Design:

• Global table: (resource_type, id) -> Arc<ResourceLockEntry>.
• ResourceLockEntry contains (Mutex<LockState>, Condvar).
• LockState:
  • owner: Option<ThreadId>
  • recursion: usize (depth for current owner)
  • refcount: usize (number of active ResourceLock handles – across all threads)
  • file: Option<File> (file whose lifetime == OS lock lifetime)

Acquisition steps (ResourceLock::acquire):

1. Lookup/insert entry in global table.
2. Lock the entry’s state.
3. If no owner: set owner = current thread, recursion = 1, refcount += 1.
   • If file is None: open + lock file (OS lock).
4. Else if owner == current thread: recursion += 1; refcount += 1.
5. Else wait on Condvar until owner released (recursion == 0), then loop.

Drop:

• Lock state, decrement recursion and refcount.
• If recursion == 0: owner = None; notify_all() to wake waiters.
• If refcount == 0: drop file (releases OS lock) and remove entry from table. Also remove the lock file on disk.

Structs

LockState 🔒

ResourceLock

Acquire a lock for a given resource type and id. Guarantees mutual exclusion across threads for a given (resource_type, id). Re-entrant acquisition by the same thread is allowed.

ResourceLockEntry 🔒

Statics

MODEL_LOCK_TABLE 🔒

Traits

Lock

Functions

check_filesystem_lock_support

get_inode_or_file_index

get_inode_or_file_index_from_descriptor

lock_table 🔒

path_and_descriptor_match

Type Aliases

LockKey 🔒