SYNOPSIS

#include <atfs.h>

Af_user *af_lock (Af_key *aso, Af_user *locker)

Af_user *af_unlock (Af_key *aso)

Af_user *af_testlock (Af_key *aso)

DESCRIPTION

This manual page describes the interface to the AtFS locking mechanism. Locks are used to avoid conflicting updates to one object history. After a user has reserved the update rights, no other user may add new versions to the reserved history. Reserving the update rights happens by locking the most recent version of the history. As AtFS allows adding new versions to each generation in a history, each generation may be locked separately. Reserving update rights for old generations (with generation numbers smaller than the newest generation) are performed by locking the most recent version of the corresponding generation. Removing an ASO (af_rm - manual page af_files(3)) and changing an ASO's version number (af_svnum - manual page af_version(3)) also requires a lock on the corresponding ASO.

af_lock reserves the update permission for the user identified by locker. On successful completion, a buffer identical to locker is returned, a NULL pointer otherwise.

af_unlock cancels a formerly established reservation of update rights. Only the owner or the locker of an ASO (identified by the Af_user structure that was given to the corresponding call of af_lock) are allowed to do this. On successful completion, af_unlock returns a buffer containing the identification of the former locker. This may be empty, if the ASO was not locked. Upon error, a NULL pointer is returned.

af_testlock returns a buffer containing an identification of the current locker of the specified ASO. It returns an empty buffer, if no lock is set.

DIAGNOSTICS

af_lock and af_unlock return -1 on error and af_errno is set to indicate the error number.