получить набор семафоров XSI (get set of XSI semaphores)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
semget — get set of XSI semaphores
Синопсис (Synopsis)
#include <sys/sem.h>
int semget(key_t key, int nsems, int semflg);
Описание (Description)
The semget() function operates on XSI semaphores (see the Base
Definitions volume of POSIX.1‐2017, Section 4.17, Semaphore). It
is unspecified whether this function interoperates with the
realtime interprocess communication facilities defined in Section
2.8, Realtime.
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.
Возвращаемое значение (Return value)
Upon successful completion, semget() shall return a non-negative
integer, namely a semaphore identifier; otherwise, it shall
return -1 and set errno to indicate the error.
Ошибки (Error)
The semget() function shall fail if:
EACCES 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.
EEXIST A semaphore identifier exists for the argument key but
((semflg &IPC_CREAT) &&(semflg &IPC_EXCL)) is non-zero.
EINVAL 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.
ENOENT A semaphore identifier does not exist for the argument key
and (semflg &IPC_CREAT) is equal to 0.
ENOSPC 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.
Примеры (Examples)
Refer to semop(3p).
Использование в приложениях (Application usage)
The POSIX Realtime Extension defines alternative interfaces for
interprocess communication. Application developers who need to
use IPC should design their applications so that modules using
the IPC routines described in Section 2.7, XSI Interprocess
Communication can be easily modified to use the alternative
interfaces.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
A future version may require that the value of the semval,
sempid, semncnt, and semzcnt members of all semaphores in a
semaphore set be initialized to zero when a call to semget()
creates a semaphore set. Many semaphore implementations already
do this and it greatly simplifies what an application must do to
initialize a semaphore set.
Смотри также (See also)
Section 2.7, XSI Interprocess Communication, Section 2.8,
Realtime, ftok(3p), semctl(3p), semop(3p), sem_close(3p),
sem_destroy(3p), sem_getvalue(3p), sem_init(3p), sem_open(3p),
sem_post(3p), sem_trywait(3p), sem_unlink(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.17,
Semaphore, sys_sem.h(0p)
