|SEMGET(3P)||POSIX Programmer's Manual||SEMGET(3P)|
int semget(key_t key, int nsems, int semflg);
The semget() function shall return the semaphore identifier associated with key.
A semaphore identifier with its associated semid_ds data structure and its associated set of nsems semaphores (see <sys/sem.h>) is created for key if one of the following is true:
- The argument key is equal to IPC_PRIVATE.
- The argument key does not already have a semaphore identifier associated with it and (semflg &IPC_CREAT) is non-zero.
Upon creation, the semid_ds data structure associated with the new semaphore identifier is initialized as follows:
- In the operation permissions structure sem_perm.cuid, sem_perm.uid, sem_perm.cgid, and sem_perm.gid shall be set to the effective user ID and effective group ID, respectively, of the calling process.
- The low-order 9 bits of sem_perm.mode shall be set to the low-order 9 bits of semflg.
- The variable sem_nsems shall be set to the value of nsems.
- The variable sem_otime shall be set to 0 and sem_ctime shall be set to the current time, as described in Section 2.7.1, IPC General Description.
- The data structure associated with each semaphore in the set need not be initialized. The semctl() function with the command SETVAL or SETALL can be used to initialize each semaphore.
- A semaphore identifier exists for key, but operation permission as specified by the low-order 9 bits of semflg would not be granted; see Section 2.7, XSI Interprocess Communication.
- A semaphore identifier exists for the argument key but ((semflg &IPC_CREAT) &&(semflg &IPC_EXCL)) is non-zero.
- The value of nsems is either less than or equal to 0 or greater than the system-imposed limit, or a semaphore identifier exists for the argument key, but the number of semaphores in the set associated with it is less than nsems and nsems is not equal to 0.
- A semaphore identifier does not exist for the argument key and (semflg &IPC_CREAT) is equal to 0.
- A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphores system-wide would be exceeded.
The following sections are informative.
The Base Definitions volume of POSIX.1‐2008, Section 4.16, Semaphore, <sys_sem.h>
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
|2013||IEEE/The Open Group|