maillock(3MAIL) 					  User Mailbox Library Functions					   maillock(3MAIL)

NAME

       maillock, mailunlock, touchlock - functions to manage lockfile(s) for user's mailbox

SYNOPSIS

       cc [ flag ... ] file ... -lmail [ library ... ]
       #include <maillock.h>

       int maillock(const char *user, int retrycnt);

       void mailunlock(void);

       void touchlock(void);

DESCRIPTION

       The  maillock()	function attempts to create a lockfile for the user's mailfile. If a lockfile already exists, and it has not been modified
       in the last 5 minutes, maillock() will remove the lockfile and set its own lockfile.

       It is crucial that programs locking mail files refresh their locks  at least every three minutes to maintain the lock. Refresh the lockfile
       by calling the touchlock() function with no arguments.

       The algorithm used to determine the age of the lockfile takes into account clock drift between machines using a network file system. A zero
       is written into the lockfile so that the lock will  be respected by systems running the standard version of System V.

       If the lockfile has been modified in the last 5 minutes	the process will sleep until the lock is available.  The  sleep  algorithm  is	to
       sleep  for  5 seconds times the attempt number. That is, the first sleep will be for 5 seconds, the next sleep will be for 10 seconds, etc.
       until the number of attempts reaches  retrycnt.

       When the lockfile is no longer needed, it should be removed by calling mailunlock().

       The user argument is the login name of the user for whose mailbox the lockfile will be created. maillock() assumes  that  user's  mailfiles
       are in the ``standard'' place as defined in  <maillock.h>.

RETURN VALUES

       Upon successful completion, .maillock() returns 0. Otherwise it returns -1.

FILES

       /var/mail/*	       user mailbox files

       /var/mail/*.lock        user mailbox lockfiles

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Unsafe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       libmail(3LIB),attributes(5)

NOTES

       The mailunlock() function will only remove the lockfile created from the most previous call to maillock(). Calling maillock() for different
       users without intervening calls to mailunlock() will cause the initially created lockfile(s) to	remain,  potentially  blocking	subsequent
       message delivery until the current process finally terminates.

SunOS 5.10							    29 Mar 1999 						   maillock(3MAIL)