uu_unlock(3) [freebsd man page]

UUCPLOCK(3)						   BSD Library Functions Manual 					       UUCPLOCK(3)

NAME

     uu_lock, uu_unlock, uu_lockerr -- acquire and release control of a serial device

LIBRARY

     System Utilities Library (libutil, -lutil)

SYNOPSIS

     #include <sys/types.h>
     #include <libutil.h>

     int
     uu_lock(const char *ttyname);

     int
     uu_lock_txfr(const char *ttyname, pid_t pid);

     int
     uu_unlock(const char *ttyname);

     const char *
     uu_lockerr(int uu_lockresult);

DESCRIPTION

     The uu_lock() function attempts to create a lock file called /var/spool/lock/LCK.. with a suffix given by the passed ttyname.  If the file
     already exists, it is expected to contain the process id of the locking program.

     If the file does not already exist, or the owning process given by the process id found in the lock file is no longer running, uu_lock() will
     write its own process id into the file and return success.

     uu_lock_txfr() transfers lock ownership to another process.  uu_lock() must have previously been successful.

     uu_unlock() removes the lockfile created by uu_lock() for the given ttyname.  Care should be taken that uu_lock() was successful before call-
     ing uu_unlock().

     uu_lockerr() returns an error string representing the error uu_lockresult, as returned from uu_lock().

RETURN VALUES

     uu_unlock() returns 0 on success and -1 on failure.

     uu_lock() may return any of the following values:

     UU_LOCK_INUSE: The lock is in use by another process.

     UU_LOCK_OK: The lock was successfully created.

     UU_LOCK_OPEN_ERR: The lock file could not be opened via open(2).

     UU_LOCK_READ_ERR: The lock file could not be read via read(2).

     UU_LOCK_CREAT_ERR: Cannot create temporary lock file via creat(2).

     UU_LOCK_WRITE_ERR: The current process id could not be written to the lock file via a call to write(2).

     UU_LOCK_LINK_ERR: Cannot link temporary lock file via link(2).

     UU_LOCK_TRY_ERR: Locking attempts are failed after 5 tries.

     If a value of UU_LOCK_OK is passed to uu_lockerr(), an empty string is returned.  Otherwise, a string specifying the reason for failure is
     returned.	uu_lockerr() uses the current value of errno to determine the exact error.  Care should be made not to allow errno to be changed
     between calls to uu_lock() and uu_lockerr().

     uu_lock_txfr() may return any of the following values:

     UU_LOCK_OK: The transfer was successful.  The specified process now holds the device lock.

     UU_LOCK_OWNER_ERR: The current process does not already own a lock on the specified device.

     UU_LOCK_WRITE_ERR: The new process id could not be written to the lock file via a call to write(2).

ERRORS

     If uu_lock() returns one of the error values above, the global value errno can be used to determine the cause.  Refer to the respective man-
     ual pages for further details.

     uu_unlock() will set the global variable errno to reflect the reason that the lock file could not be removed.  Refer to the description of
     unlink(2) for further details.

SEE ALSO

     lseek(2), open(2), read(2), write(2)

BUGS

     It is possible that a stale lock is not recognised as such if a new processes is assigned the same processes id as the program that left the
     stale lock.

     The calling process must have write permissions to the /var/spool/lock directory.	There is no mechanism in place to ensure that the permis-
     sions of this directory are the same as those of the serial devices that might be locked.

BSD
								  March 30, 1997							       BSD

Check Out this Related Man Page

pthread_rwlock_wrlock(3T)												 pthread_rwlock_wrlock(3T)

NAME

       pthread_rwlock_wrlock(), pthread_rwlock_trywrlock() - lock or attempt to lock a read-write lock for writing

SYNOPSIS

PARAMETERS

	      rwlock	Pointer to the read-write lock to be locked for writing.

DESCRIPTION

       The  function  applies  a  write lock to the read-write lock object referenced by rwlock.  The calling thread acquires the write lock if no
       other thread (reader or writer) holds the read-write lock rwlock.  Otherwise, the thread blocks (that is, it does not return from the call)
       until  it  can acquire the lock.  Results are undefined if the calling thread holds the read-write lock (whether a read or a write lock) at
       the time the call is made.

       The function applies a write lock as in the function with the exception that the function fails if any thread currently holds  rwlock  (for
       reading or writing).

       Results are undefined if any of these functions are called with an uninitialized read-write lock.

       If  a  signal  is delivered to a thread waiting for a read-write lock, upon return from the signal handler, the thread shall resume waiting
       for the read-write lock as if it was not interrupted.

RETURN VALUE

       Upon successful completion, and return zero. Otherwise, an error number is returned to indicate the error (the variable is not set).

ERRORS

       If any of the following occur, the function returns the corresponding error number:

	      [EBUSY]	     The read-write lock rwlock could not be acquired for writing because it was already locked for reading or writing.

       For each of the following conditions, if the condition is detected, the and functions return the corresponding error number:

	      [EINVAL]	     The value specified by rwlock does not refer to an initialized read-write lock.

	      [EDEADLK]      The current thread already owns the read-write lock for reading or writing.

AUTHOR

       and were developed by X/Open.

SEE ALSO

       pthread_rwlock_init(3T), pthread_rwlock_destroy(3T), pthread_rwlock_tryrdlock(3T), pthread_rwlock_rdlock(3T), pthread_rwlock_unlock(3T).

STANDARDS CONFORMANCE

								  Pthread Library					 pthread_rwlock_wrlock(3T)

Linux and UNIX Man Pages

uu_unlock(3) [freebsd man page]

Check Out this Related Man Page