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semctl.2freebsd
Langue: en
Version: 338335 (ubuntu - 24/10/10)
Section: 2 (Appels système)
BSD mandoc
NAME
semctl - control operations on a semaphore setLIBRARY
Lb libcSYNOPSIS
In sys/types.h In sys/ipc.h In sys/sem.h Ft int Fn semctl int semid int semnum int cmd ...DESCRIPTION
The Fn semctl system call performs the operation indicated by Fa cmd on the semaphore set indicated by Fa semid . A fourth argument, a Fa union semun arg , is required for certain values of Fa cmd . For the commands that use the Fa arg argument, Fa 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 Fa struct semid_ds , storing it in the memory pointed to by Fa arg.buf .
- IPC_SET
- Changes the Fa sem_perm.uid , Fa sem_perm.gid , and Fa sem_perm.mode members of the semaphore set's Fa struct semid_ds to match those of the struct pointed to by Fa arg.buf . The calling process's effective uid must match either Fa sem_perm.uid or Fa 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 Fa sem_perm.uid or Fa sem_perm.cuid , or the process must have superuser privileges.
- GETVAL
- Return the value of semaphore number Fa semnum .
- SETVAL
- Set the value of semaphore number Fa semnum to Fa arg.val . Outstanding adjust on exit values for this semaphore in any process are cleared.
- GETPID
- Return the pid of the last process to perform an operation on semaphore number Fa semnum .
- GETNCNT
- Return the number of processes waiting for semaphore number Fa semnum Ns 's value to become greater than its current value.
- GETZCNT
- Return the number of processes waiting for semaphore number Fa semnum Ns 's value to become 0.
- GETALL
- Fetch the value of all of the semaphores in the set into the array pointed to by Fa arg.array .
- SETALL
- Set the values of all of the semaphores in the set to the values in the array pointed to by Fa arg.array . Outstanding adjust on exit values for all semaphores in this set, in any process are cleared.
The Vt struct semid_ds 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 Fa cmd is one of GETVAL , GETPID , GETNCNT or GETZCNT Fn semctl returns the corresponding value; otherwise, 0 is returned. On failure, -1 is returned, and errno is set to indicate the error.ERRORS
The Fn semctl system call will fail if:- Bq Er EINVAL
- No semaphore set corresponds to Fa semid .
- Bq Er EINVAL
- The Fa semnum argument is not in the range of valid semaphores for given semaphore set.
- Bq Er EPERM
- The calling process's effective uid does not match the uid of the semaphore set's owner or creator.
- Bq Er EACCES
- Permission denied due to mismatch between operation and mode of semaphore set.
- Bq Er ERANGE
- SETVAL or SETALL attempted to set a semaphore outside the allowable range Bq 0 .. Dv SEMVMX .
SEE ALSO
semget(2), semop(2)BUGS
SETALL may update some semaphore elements before returning an error.Contenus ©2006-2024 Benjamin Poulain
Design ©2006-2024 Maxime Vantorre