semctl man page on BSDOS

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SEMCTL(2)		    BSD Programmer's Manual		     SEMCTL(2)

NAME
     semctl - control operations on a semaphore set

SYNOPSIS
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/sem.h>

     int
     semctl(int semid, int semnum, int cmd, union semun arg);

DESCRIPTION
     The semctl() function performs the operation indicated by cmd on the
     semaphore set indicated by semid. For the commands that use the arg pa-
     rameter, union semun is defined as follows:

     union semun {
	     int     val;	     /* value for SETVAL */
	     struct  semid_ds *buf;  /* buffer for IPC_STAT & IPC_SET */
	     u_short *array;	     /* array for GETALL & SETALL */
     };

     Commands are performed as follows:

     IPC_STAT	  Fetch the semaphore set's struct semid_ds, storing it in the
		  memory pointed to by arg.buf.

     IPC_SET	  Changes the sem_perm.uid, sem_perm.gid, and sem_perm.mode
		  members of the semaphore set's struct semid_ds to match
		  those of the struct pointed to by arg.buf. The calling pro-
		  cess's effective uid must match either sem_perm.uid or
		  sem_perm.cuid, or it must have superuser privileges.

     IPC_RMID	  Immediately removes the semaphore set from the system.  The
		  calling process's effective uid must equal the semaphore
		  set's sem_perm.uid or sem_perm.cuid, or the process must
		  have superuser privileges.

     GETVAL	  Return the value of semaphore number semnum.

     SETVAL	  Set the value of semaphore number semnum to arg.val.

     GETPID	  Return the pid of the last process to perform an operation
		  on semaphore number semnum.

     GETNCNT	  Return the number of processes waiting for semaphore number
		  semnum's value to become greater than its current value.

     GETZCNT	  Return the number of processes waiting for semaphore number
		  semnum's value to become 0.

     GETALL	  Fetch the value of all of the semaphores in the set into the
		  array pointed to by arg.array.

     SETALL	  Set the values of all of the semaphores in the set to the
		  values in the array pointed to by arg.array.

     The struct semid_ds structure is defined as follows:

     struct semid_ds {
	     struct  ipc_perm sem_perm;	     /* operation permission struct */
	     struct  sem *sem_base;	     /* pointer to first semaphore in set */
	     u_short sem_nsems;		     /* number of sems in set */
	     time_t  sem_otime;		     /* last operation time */
	     time_t  sem_ctime;		     /* last change time */
					     /* Times measured in secs since */
					     /* 00:00:00 GMT, Jan. 1, 1970 */
     };

RETURN VALUES
     On success, when cmd is one of GETVAL, GETNCNT, or GETZCNT, semctl() re-
     turns the corresponding value; otherwise, 0 is returned.  On failure, -1
     is returned, and errno is set to indicate the error.

ERRORS
     The semctl() function will fail if:

     [EINVAL]	   No semaphore set corresponds to semid.

     [EINVAL]	   semnum is not in the range of valid semaphores for given
		   semaphore set.

     [EPERM]	   The calling process's effective uid does not match the uid
		   of the semaphore set's owner or creator.

     [EACCES]	   Permission denied due to mismatch between operation and
		   mode of semaphore set.

SEE ALSO
     semget(2),	 semop(2)

4th Berkeley Distribution	 July 3, 1996				     2
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