Manual browser: semget(2)
|SEMGET(2)||System Calls Manual||SEMGET(2)|
NAMEsemget — get set of semaphores
LIBRARYStandard C Library (libc, -lc)
semget(key_t key, int nsems, int semflg);
DESCRIPTIONThe semget() system call returns the semaphore identifier associated with key.
A new set containing nsems semaphores is created if either key is equal to IPC_PRIVATE, or key does not have a semaphore set associated with it and the IPC_CREAT bit is set in semflg. If both the IPC_CREAT bit and the IPC_EXCL bit are set in semflg, and key has a semaphore set associated with it already, the operation will fail.
If a new set of semaphores is created, the data structure associated with it (the semid_ds structure, see semctl(2)) is initialized as follows:
- sem_perm.cuid and sem_perm.uid are set to the effective uid of the calling process.
- sem_perm.gid and sem_perm.cgid are set to the effective gid of the calling process.
- sem_perm.mode is set to the lower 9 bits of semflg.
- sem_nsems is set to the value of nsems.
- sem_ctime is set to the current time.
- sem_otime is set to 0.
RETURN VALUESsemget() returns a non-negative semaphore identifier if successful. Otherwise, -1 is returned and errno is set to reflect the error.
- The caller has no permission to access a semaphore set already associated with key.
- Both IPC_CREAT and IPC_EXCL are set in semflg, and a semaphore set is already associated with key.
nsems is less than 0 or greater than the system limit for the number in a semaphore set.
A semaphore set associated with key exists, but has fewer semaphores than the number specified in nsems.
- A new set of semaphores could not be created because the system limit for the number of semaphores or the number of semaphore sets has been reached.
- IPC_CREAT is not set in semflg and no semaphore set associated with key was found.
STANDARDSThe semget system call conforms to X/Open System Interfaces and Headers Issue 5 (“XSH5”).
HISTORYSemaphores appeared in the first release of AT&T System V UNIX.
|May 13, 2004||NetBSD 7.0|