получить идентификатор очереди сообщений XSI (get the XSI message queue identifier)
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)
msgget — get the XSI message queue identifier
Синопсис (Synopsis)
#include <sys/msg.h>
int msgget(key_t key, int msgflg);
Описание (Description)
The msgget() function operates on XSI message queues (see the
Base Definitions volume of POSIX.1‐2017, Section 3.226, Message
Queue). It is unspecified whether this function interoperates
with the realtime interprocess communication facilities defined
in Section 2.8, Realtime.
The msgget() function shall return the message queue identifier
associated with the argument key.
A message queue identifier, associated message queue, and data
structure (see <sys/msg.h>), shall be created for the argument
key if one of the following is true:
* The argument key is equal to IPC_PRIVATE.
* The argument key does not already have a message queue
identifier associated with it, and (msgflg & IPC_CREAT) is
non-zero.
Upon creation, the data structure associated with the new message
queue identifier shall be initialized as follows:
* msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_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 msg_perm.mode shall be set to the
low-order 9 bits of msgflg.
* msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime
shall be set to 0.
* msg_ctime shall be set to the current time, as described in
Section 2.7.1, IPC General Description.
* msg_qbytes shall be set to the system limit.
Возвращаемое значение (Return value)
Upon successful completion, msgget() shall return a non-negative
integer, namely a message queue identifier. Otherwise, it shall
return -1 and set errno to indicate the error.
Ошибки (Error)
The msgget() function shall fail if:
EACCES A message queue identifier exists for the argument key,
but operation permission as specified by the low-order 9
bits of msgflg would not be granted; see Section 2.7, XSI
Interprocess Communication.
EEXIST A message queue identifier exists for the argument key but
((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is non-zero.
ENOENT A message queue identifier does not exist for the argument
key and (msgflg & IPC_CREAT) is 0.
ENOSPC A message queue identifier is to be created but the
system-imposed limit on the maximum number of allowed
message queue identifiers system-wide would be exceeded.
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
The POSIX Realtime Extension defines alternative interfaces for
interprocess communication (IPC). 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)
None.
Смотри также (See also)
Section 2.7, XSI Interprocess Communication, Section 2.8,
Realtime, ftok(3p), mq_close(3p), mq_getattr(3p), mq_notify(3p),
mq_open(3p), mq_receive(3p), mq_send(3p), mq_setattr(3p),
mq_unlink(3p), msgctl(3p), msgrcv(3p), msgsnd(3p)
The Base Definitions volume of POSIX.1‐2017, Section 3.226,
Message Queue, sys_msg.h(0p)
