scheme-libraries/retropikzel/dot-locking

Dot locking for files

This is an implementation of dot-locking from scsh.

Documentation

From https://scsh.net/docu/html/man-Z-H-11.html#node_sec_10.3

Copied here for convenience.

(obtain-dot-lock file-name)

Tries to obtain the lock for file-name. If the file is already locked, the thread sleeps for interval seconds (default is 1) before it retries. If the lock cannot be obtained after retry-number attempts, the procedure returns #f, other- wise #t. The default value of retry-number is #f which corresponds to an infinite number of retires. If stale-time is non-#f, it specifies the minimum age a lock may have (in seconds) before it is considered stale. Obtain-dot-lock attempts to delete stale locks. If it was succcessful obtaining a lock after breaking it, obtain-dot-lock returns broken. If stale-time is #f, obtain-dot-lock never considers a lock stale. The default for stale-time is 300. Note that it is possible that obtain-dot-lock breaks a lock but never- theless fails to obtain it otherwise. If it is necessary to handle this case specially, use break-dot-lock directly (see below) rather than specifying a non-#f stale-time

(break-dot-lock file-name)

Breaks the lock for file-name if one exists. Note that breaking a lock does not imply a subsequent obtain-dot-lock will succeed, as an- other party may have acquired the lock between break-dot-lock and obtain-dot-lock.

(release-dot-lock file-name)

Releases the lock for file-name. On success, release-dot-lock returns #t, otherwise #f. Note that this procedure can also be used to break the lock for file-name.

(with-dot-lock* file-name thunk) (with-dot-lock file-name body ...)

The procedure with-dot-lock* obtains the requested lock, and then calls (thunk). When thunk returns, the lock is released. A non-local exit (e.g., throwing to a saved continuation or raising an exception) also causes the lock to be released. After a normal return from thunk, its return values are returned by with-dot-lock*. The with-dot-lock special form is equivalent syntac- tic sugar.