SEMGET(2) BSD Programmer's Manual SEMGET(2)
semget - get semaphore set
#include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h> int semget(key_t key, int nsems, int semflg);
The 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. The access modes of the created semaphores is specified in semflg by OR'ing the following values: SEM_A alter permission for owner SEM_R read permission for owner SEM_A >> 3 alter permission for group SEM_R >> 3 read permission for group SEM_A >> 6 alter permission for other SEM_R >> 6 read permission for other 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.
semget() returns a non-negative semaphore identifier if successful. Oth- erwise, -1 is returned and errno is set to reflect the error.
[EACCES] The caller has no permission to access a semaphore set al- ready associated with key. [EEXIST] Both IPC_CREAT and IPC_EXCL are set in semflg, and a sema- phore set is already associated with key. [EINVAL] nsems is less than or equal to 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. [ENOSPC] 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. [ENOENT] IPC_CREAT was not set in semflg and no semaphore set asso- ciated with key was found.
semctl(2), semop(2), ftok(3) MirOS BSD #10-current August 17, 1995 1
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