PIDLOCK(3) | Library Functions Manual | PIDLOCK(3) |
pidlock
, ttylock
,
ttyunlock
—
#include <util.h>
int
pidlock
(const
char *lockfile, int
flags, pid_t
*locker, const char
*info);
int
ttylock
(const
char *tty, int
flags, pid_t
*locker);
int
ttyunlock
(const
char *tty);
pidlock
() ttylock
(), and
ttyunlock
() functions attempt to create a lockfile for
an arbitrary resource that only one program may hold at a time. (In the case
of ttylock
(), this is access to a tty device.) If the
function succeeds in creating the lockfile, it will succeed for no other
program calling it with the same lockfile until the original calling program
has removed the lockfile or exited. The ttyunlock
()
function will remove the lockfile created by
ttylock
().
These functions use the method of creating a lockfile traditionally used by UUCP software. This is described as follows in the documentation for Taylor UUCP:
The PID is stored in ASCII format, with leading spaces to pad it
out to ten characters, and a terminating newline. This implementation has
been extended to put the hostname on the second line of the file, terminated
with a newline, and optionally an arbitrary comment on the third line of the
file, also terminated with a newline. If a comment is given, but
PIDLOCK_NONBLOCK
is not, a blank line will be
written as the second line of the file.
The pidlock
() function will attempt to
create the file lockfile and put the current process's
pid in it. The ttylock
() function will do the same,
but should be passed only the base name (with no leading directory prefix)
of the tty to be locked; it will test that the tty
exists in /dev and is a character device, and then
create the file in the /var/spool/lock directory and
prefix the filename with LCK... Use the
ttyunlock
() function to remove this lock.
The following flags may be passed in flags:
PIDLOCK_NONBLOCK
PIDLOCK_USEHOSTNAME
PIDLOCK_USEHOSTNAME
is specified and no
hostname is present.)If locker is non-null, it will contain the PID of the locking process, if there is one, on return.
If info is non-null and the lock succeeds, the string it points to will be written as the third line of the lock file.
pidlock
() or ttylock
() can set
errno to the following values on failure:
EFTYPE
]ttylock
() is not a character special device.EWOULDBLOCK
]PIDLOCK_NONBLOCK
flag was specified.pidlock
() and ttylock
()
functions appeared in NetBSD 1.3.
The PID returned will be the pid of the locker on the remote
machine if PIDLOCK_USEHOSTNAME
is specified, but
there is no indication that this is not on the local machine.
March 19, 2006 | NetBSD 9.2 |