SEMGET(2) System Calls Manual SEMGET(2)

semgetobtain a semaphore id

#include <sys/sem.h>

int
semget(key_t key, int nsems, int semflg);

Based on the values of key and semflg, () returns the identifier of a newly created or previously existing set of semaphores. The key is analogous to a filename: it provides a handle that names an IPC object. There are three ways to specify a key:

The mode of a newly created IPC object is determined by 'ing the following constants into the semflg argument:

Read access for user.
Alter access for user.
(SEM_R>>3)
Read access for group.
(SEM_A>>3)
Alter access for group.
(SEM_R>>6)
Read access for other.
(SEM_A>>6)
Alter access for other.

If a new set of semaphores is being created, nsems is used to indicate the number of semaphores the set should contain. Otherwise, nsems may be specified as 0.

The semget() system call returns the id of a semaphore set if successful; otherwise, -1 is returned and errno is set to indicate the error.

The semget() system call will fail if:

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Access permission failure.
[]
IPC_CREAT and IPC_EXCL were specified, and a semaphore set corresponding to key already exists.
[]
The number of semaphores requested is either less than 1 or greater than the system imposed maximum per set.
[]
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 non-zero.
[]
No semaphore set was found corresponding to key, and IPC_CREAT was not specified.
[]
Insufficiently many semaphores are available.
[]
The kernel could not allocate a struct semid_ds.

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

The include files <sys/types.h> and <sys/ipc.h> are necessary.

semctl(2), semop(2), ftok(3), compat(5)

September 12, 1995 macOS 14.4