mirror of https://github.com/mkerrisk/man-pages
New pages for POSIX message queues API
This commit is contained in:
Michael Kerrisk
parent
b8798cc43f
commit
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'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
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.\"
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||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
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.TH MQ_CLOSE 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
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.SH NAME
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mq_close \- close a message queue descriptor
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.SH SYNOPSIS
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.nf
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.B #include <mqueue.h>
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.sp
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.BI "mqd_t mq_close(mqd_t " mqdes );
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.fi
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.SH DESCRIPTION
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.BR mq_close ()
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closes the message queue descriptor
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.IR mqdes .
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If the calling process has attached a notification request
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to this message queue via
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.IR mqdes ,
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then this request is removed,
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and another process can now attach a notification request.
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.SH NOTES
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All open message queues are automatically closed on process termination,
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or upon
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.BR execve (2).
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.SH RETURN VALUE
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On success
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.BR mq_close ()
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returns 0; on error, \-1 is returned, with
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.I errno
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set to indicate the error.
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.SH ERRORS
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.TP
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.B EBADF
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The descriptor specified in
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.I mqdes
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is invalid.
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR mq_getattr (3),
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.BR mq_notify (3),
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.BR mq_open (3),
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.BR mq_receive (3),
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.BR mq_send (3),
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.BR mq_unlink (3),
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.BR mq_overview (7)
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|
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@ -0,0 +1,140 @@
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'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_GETATTR 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
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.SH NAME
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mq_getattr, mq_setattr \- get/set message queue attributes
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.SH SYNOPSIS
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.nf
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.B #include <mqueue.h>
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.sp
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.BI "mqd_t mq_getattr(mqd_t " mqdes ", struct mq_attr *" attr );
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.BI "mqd_t mq_setattr(mqd_t " mqdes ", struct mq_attr *" newattr ","
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.BI " struct mq_attr *" oldattr );
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.fi
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.SH DESCRIPTION
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.BR mq_getattr ()
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and
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.BR mq_setattr ()
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respectively retrieve and modify attributes of the message queue
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referred to by the descriptor
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.IR mqdes .
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.BR mq_getattr ()
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returns an
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.I mq_attr
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structure in the buffer pointed by
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.IR attr.
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This structure is defined as:
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.in +0.25i
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.nf
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struct mq_attr {
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long mq_flags; /* Flags: 0 or O_NONBLOCK */
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long mq_maxmsg; /* Max. # of messages on queue */
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long mq_msgsize; /* Max. message size (bytes) */
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long mq_curmsgs; /* # of messages currently in queue */
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};
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.fi
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.in -0.25i
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.PP
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The
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.I mq_flags
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field contains flags associated with the open message queue description.
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This field is initialised when the queue is created by
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.BR mq_open ().
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The only flag that can appear in this field is
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.BR O_NONBLOCK .
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The
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.I mq_maxmsg
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and
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.I mq_msgsize
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fields are set when the message queue is created by
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.BR mq_open ().
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The
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.I mq_maxmsg
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field is an upper limit on the number of messages
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that may be placed on the queue using
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.BR mq_send ().
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The
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.I mq_msgsize
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field is an upper limit on the size of messages
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that may be placed on the queue.
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Both of these fields must have a value greater than zero.
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Two
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.I /proc
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files that place ceilings on the values for these fields are described in
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.BR mq_open (3).
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The
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.I mq_curmsgs
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field returns the number of messages currently held in the queue.
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.BR mq_setattr ()
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sets message queue attributes using information supplied in the
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.I mq_attr
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structure pointed to by
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.IR newattr .
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The only attribute that can be modified is the setting of the
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.B O_NONBLOCK
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flag in
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.IR mq_flags .
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The other fields in
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.I newattr
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are ignored.
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If the
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.I oldattr
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field is not NULL,
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then the buffer that it points to is used to return an
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.I mq_attr
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structure that contains the same information that is returned by
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.BR mq_getattr ().
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.SH RETURN VALUE
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On success
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.BR mq_getattr ()
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and
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.BR mq_setattr ()
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return 0; on error, \-1 is returned, with
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.I errno
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set to indicate the error.
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.SH ERRORS
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.TP
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.B EBADF
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The descriptor specified in
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.I mqdes
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is invalid.
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.TP
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.B EINVAL
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.I newattr->mq_flags
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contained set bits other than
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.BR O_NONBLOCK .
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR mq_close (3),
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.BR mq_notify (3),
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.BR mq_open (3),
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.BR mq_receive (3),
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.BR mq_send (3),
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.BR mq_unlink (3),
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.BR mq_overview (7)
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|
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@ -0,0 +1,256 @@
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'\" t
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.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
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.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_NOTIFY 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
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.SH NAME
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mq_notify \- register for notification when a message is available
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.SH SYNOPSIS
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.nf
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.B #include <mqueue.h>
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.sp
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.BI "mqd_t mq_notify(mqd_t " mqdes ", const struct sigevent *" notification );
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.fi
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.SH DESCRIPTION
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.BR mq_notify ()
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allows the calling process to register or unregister for delivery of
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an asynchronous notification when a new message arrives on
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the empty message queue referred to by the descriptor
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.IR mqdes .
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The
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.I notification
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argument is a pointer to a
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.I sigevent
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structure that is defined something like the following:
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.in +0.25i
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.nf
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union sigval { /* Data passed with notification */
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int sival_int; /* Integer value */
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void *sival_ptr; /* Pointer value */
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};
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struct sigevent {
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int sigev_notify; /* Notification method */
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int sigev_signal; /* Notification signal */
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union sigval sigev_value; /* Data passed with notification */
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void (*sigev_notify_function) (union sigval);
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/* Function for thread notification */
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void *sigev_notify_attributes;
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/* Thread function attributes */
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};
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.fi
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.in -0.25i
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|
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If
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.I notification
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is a non-NULL pointer, then
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.BR mq_notify ()
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registers the calling process to receive message notification.
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The
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.I sigev_notify
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field of the
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.I sigevent
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to which
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.I notification
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points specifies how notification is to be performed.
|
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This field has one of the following values:
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.TP
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.B SIGEV_NONE
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A "null" notification: the calling process is registered as the target
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for notification, but when a message arrives, no notification is sent.
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.\" When is SIGEV_NONE useful?
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.TP
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.B SIGEV_SIGNAL
|
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Notify the process by sending the signal specified in
|
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.IR sigev_signal .
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If the signal is caught with a signal handler that
|
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was registered using the
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.BR sigaction (2)
|
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.B SA_SIGINFO
|
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flag, then the following fields are set in the
|
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.I siginfo_t
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structure that is passed as the second argument of the handler:
|
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.I si_code
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is set to
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.BR SI_MESGQ ;
|
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.I si_signo
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is set to the signal number;
|
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.I si_value
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is set to the value specified in
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.IR notification->sigev_value ;
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.\" I don't know of other implementations that set
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.\" si_pid and si_uid -- MTK
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.I si_pid
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is set to the PID of the process that sent the message; and
|
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.I si_uid
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is set to the real user ID of the sending process.
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.TP
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.B SIGEV_THREAD
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Deliver notification by invoking
|
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.I notification->sigev_thread_function
|
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as the start function of a new thread.
|
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The function is invoked with
|
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.IR notification->sigev_value
|
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as its sole argument.
|
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If
|
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.IR notification->sigev_notify_attributes
|
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is not NULL, then it should point to a
|
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.I pthread_attr_t
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structure that defines attributes for the thread.
|
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.\" FIXME add a cross reference to pthread_attr_init(3), when
|
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.\" that page is one day written.
|
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.PP
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Only one process can be registered to receive notification
|
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from a message queue.
|
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|
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If
|
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.I notification
|
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is NULL, and the calling process is currently registered to receive
|
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notifications for this message queue, then the registration is removed;
|
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another process can then register to receive a message notification
|
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for this queue.
|
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|
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Message notification only occurs when a new message arrives and
|
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the queue was previously empty.
|
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If the queue was not empty at the time
|
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.BR mq_notify ()
|
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was called, then a notification will only occur after
|
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the queue is emptied and a new message arrives.
|
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|
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If another process or thread is waiting to read a message
|
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from an empty queue using
|
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.BR mq_receive (),
|
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then any message notification registration is ignored:
|
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the message is delivered to the process or thread calling
|
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.BR mq_receive (),
|
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and the message notification registration remains in effect.
|
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|
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Notification occurs once: after a notification is delivered,
|
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the notification registration is removed,
|
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and another process can register for message notification.
|
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If the notified process wishes to receive the next notification,
|
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it can use
|
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.BR mq_notify ()
|
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to request a further notification.
|
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This should be done before emptying all unread messages from the queue.
|
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(Placing the queue in non-blocking mode is useful for emptying
|
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the queue of messages without blocking once it is empty.)
|
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.SH RETURN VALUE
|
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On success
|
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.BR mq_notify ()
|
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returns 0; on error, \-1 is returned, with
|
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.I errno
|
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set to indicate the error.
|
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.SH ERRORS
|
||||
.TP
|
||||
.B EBADF
|
||||
The descriptor specified in
|
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.I mqdes
|
||||
is invalid.
|
||||
.TP
|
||||
.B EBUSY
|
||||
Another process has already registered to receive notification
|
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for this message queue.
|
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.TP
|
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.B EINVAL
|
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.I notification->sigev_notify
|
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is not one of the permitted values; or
|
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.I notification->sigev_notify
|
||||
is
|
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.B SIGEV_SIGNAL
|
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and
|
||||
.I notification->sigev_signo
|
||||
is not a a valid signal number.
|
||||
.TP
|
||||
.B ENOMEM
|
||||
Insufficient memory.
|
||||
.SH CONFORMING TO
|
||||
POSIX.1-2001.
|
||||
.SH EXAMPLE
|
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The following program registers a notification request for the
|
||||
message queue named in its command-line argument.
|
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Notification is performed by creating a thread.
|
||||
The thread executes a function which reads one message from the
|
||||
queue and then terminates the process.
|
||||
.nf
|
||||
|
||||
#include <pthread.h>
|
||||
#include <mqueue.h>
|
||||
#include <assert.h>
|
||||
#include <stdio.h>
|
||||
#include <stdlib.h>
|
||||
#include <unistd.h>
|
||||
|
||||
#define die(msg) { perror(msg); exit(EXIT_FAILURE); }
|
||||
|
||||
static void /* Thread start function */
|
||||
tfunc(union sigval sv)
|
||||
{
|
||||
struct mq_attr attr;
|
||||
ssize_t nr;
|
||||
void *buf;
|
||||
mqd_t mqdes = *((mqd_t *) sv.sival_ptr);
|
||||
|
||||
/* Determine max. msg size; allocate buffer to receive msg */
|
||||
|
||||
if (mq_getattr(mqdes, &attr) == -1) die("mq_getattr");
|
||||
buf = malloc(attr.mq_msgsize);
|
||||
if (buf == NULL) die("malloc");
|
||||
|
||||
nr = mq_receive(mqdes, buf, attr.mq_msgsize, NULL);
|
||||
if (nr == -1) die("mq_receive");
|
||||
|
||||
printf("Read %ld bytes from MQ\n", (long) nr);
|
||||
free(buf);
|
||||
exit(EXIT_SUCCESS); /* Terminate the process */
|
||||
}
|
||||
|
||||
int
|
||||
main(int argc, char *argv[])
|
||||
{
|
||||
mqd_t mqdes;
|
||||
struct sigevent not;
|
||||
|
||||
assert(argc == 2);
|
||||
|
||||
mqdes = mq_open(argv[1], O_RDONLY);
|
||||
if (mqdes == (mqd_t) -1) die("mq_open");
|
||||
|
||||
not.sigev_notify = SIGEV_THREAD;
|
||||
not.sigev_notify_function = tfunc;
|
||||
not.sigev_notify_attributes = NULL;
|
||||
not.sigev_value.sival_ptr = &mqdes; /* Arg. to thread func. */
|
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if (mq_notify(mqdes, ¬) == -1) die("mq_notify");
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||||
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pause(); /* Process will be terminated by thread function */
|
||||
}
|
||||
.fi
|
||||
.SH "SEE ALSO"
|
||||
.BR mq_close (3),
|
||||
.BR mq_getattr (3),
|
||||
.BR mq_open (3),
|
||||
.BR mq_receive (3),
|
||||
.BR mq_send (3),
|
||||
.BR mq_unlink (3),
|
||||
.BR mq_overview (7)
|
||||
|
|
@ -0,0 +1,214 @@
|
|||
'\" t
|
||||
.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_OPEN 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
mq_open \- open a message queue
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <mqueue.h>
|
||||
.sp
|
||||
.BI "mqd_t mq_open(const char *" name ", int " oflag );
|
||||
.BI "mqd_t mq_open(const char *" name ", int " oflag ", mode_t " mode ", mq_attr " attr );
|
||||
.fi
|
||||
.SH DESCRIPTION
|
||||
.BR mq_open ()
|
||||
creates a new POSIX message queue or opens an existing queue.
|
||||
The queue is identified by
|
||||
.IR name .
|
||||
For details of the construction of
|
||||
.IR name ,
|
||||
see
|
||||
.BR mq_overview (7).
|
||||
|
||||
The
|
||||
.I oflag
|
||||
argument specifies flags that control the operation of the call.
|
||||
Exactly one of the following must be specified in
|
||||
.IR oflag:
|
||||
.TP
|
||||
.B O_RDONLY
|
||||
Open the queue to receive messages only.
|
||||
.TP
|
||||
.B O_WRONLY
|
||||
Open the queue to send messages only.
|
||||
.TP
|
||||
.B O_RDWR
|
||||
Open the queue to both send and receive messages.
|
||||
.PP
|
||||
Zero or more of the following flags can additionally be
|
||||
.IR OR ed
|
||||
in
|
||||
.IR oflag :
|
||||
.TP
|
||||
.B O_NONBLOCK
|
||||
Open the queue in non-blocking mode.
|
||||
In circumstances where
|
||||
.BR mq_receive ()
|
||||
and
|
||||
.BR mq_send ()
|
||||
would normally block, these functions instead fail with the error
|
||||
.BR EAGAIN .
|
||||
.TP
|
||||
.B O_CREAT
|
||||
Create the message queue if it does not exist.
|
||||
The owner (user ID) of the message queue is set to the effective
|
||||
user ID of the calling process.
|
||||
The group ownership (group ID) is set to the effective group ID
|
||||
of the calling process.
|
||||
.\" In reality the file system IDs are used on Linux.
|
||||
.TP
|
||||
.B O_EXCL
|
||||
If
|
||||
.B O_CREAT
|
||||
was specified in
|
||||
.IR oflag ,
|
||||
and a queue with the given
|
||||
.I name
|
||||
already exists, then fail with the error
|
||||
.BR EEXIST .
|
||||
.PP
|
||||
If
|
||||
.B O_CREAT
|
||||
is specified in
|
||||
.IR oflag ,
|
||||
then two additional arguments must be supplied.
|
||||
The
|
||||
.I mode
|
||||
argument specifies the permissions to be placed on the new queue,
|
||||
as for
|
||||
.BR open (2).
|
||||
The permissions settings are masked against the process umask.
|
||||
The
|
||||
.I attr
|
||||
argument specifies attributes for the queue. See
|
||||
.BR mq_getattr (2)
|
||||
for details.
|
||||
If
|
||||
.I attr
|
||||
is NULL, then the queue is created with implementation-defined
|
||||
default attributes.
|
||||
.SH RETURN VALUE
|
||||
On success,
|
||||
.BR mq_open ()
|
||||
returns a message queue descriptor for use by other
|
||||
message queue functions.
|
||||
On error,
|
||||
.BR mq_open ()
|
||||
returns
|
||||
.IR "(mqd_t)\ \-1",
|
||||
with
|
||||
.I errno
|
||||
set to indicate the error.
|
||||
.SH ERRORS
|
||||
.TP
|
||||
.B EACCESS
|
||||
The queue exists, but the caller does not have permission to
|
||||
open it in the specified mode.
|
||||
.TP
|
||||
.B EINVAL
|
||||
.B O_CREAT
|
||||
was specified in
|
||||
.IR oflag ,
|
||||
and
|
||||
.I attr
|
||||
was not NULL, but
|
||||
.I attr->mq_maxmsg
|
||||
or
|
||||
.I attr->mq_msqsize
|
||||
was invalid.
|
||||
Both of these fields must be greater than zero.
|
||||
In a process that is unprivileged (does not have the
|
||||
.B CAP_SYS_RESOURCE
|
||||
capability),
|
||||
.I attr->mq_maxmsg
|
||||
must be less than or equal to the
|
||||
.I msg_max
|
||||
limit, and
|
||||
.I attr->mq_msgsize
|
||||
must be less than or equal to the
|
||||
.I msgsize_max
|
||||
limit.
|
||||
In addition, even in a privileged process,
|
||||
.I attr->mq_maxmsg
|
||||
cannot exceed the
|
||||
.B HARD_MAX
|
||||
limit.
|
||||
(See
|
||||
.BR mq_overview (7)
|
||||
for details of these limits.)
|
||||
.TP
|
||||
.B EEXIST
|
||||
Both
|
||||
.B O_CREAT
|
||||
and
|
||||
.B O_EXCL
|
||||
were specified in
|
||||
.IR oflag ,
|
||||
but a queue with this
|
||||
.I name
|
||||
already exists.
|
||||
.TP
|
||||
.B EMFILE
|
||||
The process already has the maximum number of files and
|
||||
message queues open.
|
||||
.TP
|
||||
.B ENAMETOOLONG
|
||||
.IR name
|
||||
was too long.
|
||||
.TP
|
||||
.B ENFILE
|
||||
The system limit on the total number of open files and message queues
|
||||
has been reached.
|
||||
.TP
|
||||
.B ENOENT
|
||||
The
|
||||
.B O_CREAT
|
||||
flag was not specified in
|
||||
.IR oflag ,
|
||||
and no queue with this
|
||||
.I name
|
||||
exists.
|
||||
.TP
|
||||
.B ENOMEM
|
||||
Insufficient memory.
|
||||
.TP
|
||||
.B ENOSPC
|
||||
Insufficient space for the creation of a new message queue.
|
||||
This probably occurred because the
|
||||
.I queues_max
|
||||
limit was encountered; see
|
||||
.BR mq_overview (7).
|
||||
.SH CONFORMING TO
|
||||
POSIX.1-2001.
|
||||
.SH BUGS
|
||||
In kernels before 2.6.14,
|
||||
the process umask was not applied to the permissions specified in
|
||||
.IR mode .
|
||||
.SH "SEE ALSO"
|
||||
.BR mq_close (3),
|
||||
.BR mq_getattr (3),
|
||||
.BR mq_notify (3),
|
||||
.BR mq_receive (3),
|
||||
.BR mq_send (3),
|
||||
.BR mq_unlink (3),
|
||||
.BR mq_overview (7)
|
||||
|
|
@ -0,0 +1,148 @@
|
|||
'\" t
|
||||
.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_RECEIVE 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
mq_receive, mq_timedreceive \- receive a message from a message queue
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <mqueue.h>
|
||||
.sp
|
||||
.BI "mqd_t mq_receive(mqd_t " mqdes ", char *" msg_ptr ,
|
||||
.BI " size_t " msg_len ", unsigned *" msg_prio );
|
||||
.sp
|
||||
.B #define _XOPEN_SOURCE 600
|
||||
.B #include <time.h>
|
||||
.B #include <mqueue.h>
|
||||
.sp
|
||||
.BI "mqd_t mq_timedreceive(mqd_t " mqdes ", char *" msg_ptr ,
|
||||
.BI " size_t " msg_len ", unsigned *" msg_prio ,
|
||||
.BI " const struct timespec *" abs_timeout );
|
||||
.fi
|
||||
.SH DESCRIPTION
|
||||
.BR mq_receive ()
|
||||
removes the oldest message with the highest priority from
|
||||
the message queue referred to by the descriptor
|
||||
.IR mqdes ,
|
||||
and places it in the buffer pointed to by
|
||||
.IR msg_ptr .
|
||||
The
|
||||
.I msg_len
|
||||
argument specifies the size of the buffer pointed to by
|
||||
.IR msg_ptr ;
|
||||
this must be greater than the
|
||||
.I mq_msgsize
|
||||
attribute of the queue (see
|
||||
.BR mq_getattr (3)).
|
||||
If
|
||||
.I prio
|
||||
is not NULL, then the buffer to which it points is used
|
||||
to return the priority associated with the received message.
|
||||
|
||||
If the queue is empty, then, by default,
|
||||
.BR mq_receive ()
|
||||
blocks until a message becomes available,
|
||||
or the call is interrupted by a signal handler.
|
||||
If the
|
||||
.B O_NONBLOCK
|
||||
flag is enabled for the message queue description,
|
||||
then the call instead fails immediately with the error
|
||||
.BR EAGAIN .
|
||||
|
||||
.BR mq_timedreceive ()
|
||||
behaves just like
|
||||
.BR mq_receive (),
|
||||
except that if the queue is empty and the
|
||||
.B O_NONBLOCK
|
||||
flag is not enabled for the message queue description, then
|
||||
.I abs_timeout
|
||||
points to a structure which specifies a ceiling on the time for which
|
||||
the call will block.
|
||||
This ceiling is an absolute timeout in seconds and nanoseconds
|
||||
since the Epoch (midnight on the morning of 1 January 1970),
|
||||
specified in the following structure:
|
||||
.sp
|
||||
.RS
|
||||
.nf
|
||||
struct timespec {
|
||||
time_t tv_sec; /* seconds */
|
||||
long tv_nsec; /* nanoseconds */
|
||||
};
|
||||
|
||||
.fi
|
||||
.RE
|
||||
If no message is available,
|
||||
and the timeout has already expired by the time of the call,
|
||||
.BR mq_timedreceive ()
|
||||
returns immediately.
|
||||
.SH RETURN VALUE
|
||||
On success,
|
||||
.BR mq_receive ()
|
||||
and
|
||||
.BR mq_timedreceive ()
|
||||
return the number of bytes in the received message;
|
||||
on error, \-1 is returned, with
|
||||
.I errno
|
||||
set to indicate the error.
|
||||
.SH ERRORS
|
||||
.TP
|
||||
.B EAGAIN
|
||||
The queue was empty, and the
|
||||
.B O_NONBLOCK
|
||||
flag was set for the message queue description referred to by
|
||||
.IR mqdes .
|
||||
.TP
|
||||
.B EBADF
|
||||
The descriptor specified in
|
||||
.I mqdes
|
||||
was invalid.
|
||||
.TP
|
||||
.B EMSGSIZE
|
||||
.IR msg_len
|
||||
was less than the
|
||||
.I mq_msgsize
|
||||
attribute of the message queue.
|
||||
.TP
|
||||
.B EINTR
|
||||
The call was interrupted by a signal handler.
|
||||
.TP
|
||||
.B EINVAL
|
||||
The call would have blocked, and
|
||||
.I abs_timeout
|
||||
was invalid, either because
|
||||
.I tv_sec
|
||||
was less than zero, or because
|
||||
.I tv_nsec
|
||||
was less than zero or greater than 1000 million.
|
||||
.TP
|
||||
.B ETIMEDOUT
|
||||
The call timed out before a message could be transferred.
|
||||
.SH CONFORMING TO
|
||||
POSIX.1-2001.
|
||||
.SH "SEE ALSO"
|
||||
.BR mq_close (3),
|
||||
.BR mq_getattr (3),
|
||||
.BR mq_notify (3),
|
||||
.BR mq_open (3),
|
||||
.BR mq_send (3),
|
||||
.BR mq_unlink (3),
|
||||
.BR mq_overview (7)
|
||||
|
|
@ -0,0 +1,153 @@
|
|||
'\" t
|
||||
.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_SEND 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
mq_send, mq_timedsend \- send a message to a message queue
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <mqueue.h>
|
||||
.sp
|
||||
.BI "mqd_t mq_send(mqd_t " mqdes ", const char *" msg_ptr ,
|
||||
.BI " size_t " msg_len ", unsigned " msg_prio );
|
||||
.sp
|
||||
.B #define _XOPEN_SOURCE 600
|
||||
.B #include <time.h>
|
||||
.B #include <mqueue.h>
|
||||
.sp
|
||||
.BI "mqd_t mq_timedsend(mqd_t " mqdes ", const char *" msg_ptr ,
|
||||
.BI " size_t " msg_len ", unsigned " msg_prio ,
|
||||
.BI " const struct timespec *" abs_timeout );
|
||||
.fi
|
||||
.SH DESCRIPTION
|
||||
.BR mq_send ()
|
||||
adds the message pointed to by
|
||||
.IR msg_ptr
|
||||
to the message queue referred to by the descriptor
|
||||
.IR mqdes .
|
||||
The
|
||||
.I msg_len
|
||||
argument specifies the length of the message pointed to by
|
||||
.IR msg_ptr ;
|
||||
this length must be less than or equal to the queue's
|
||||
.I mq_msgsize
|
||||
attribute.
|
||||
Zero-length messages are allowed.
|
||||
|
||||
The
|
||||
.I msg_prio
|
||||
argument is a non-negative integer that specifies the priority
|
||||
of this message.
|
||||
Messages are placed on the queue in decreasing order of priority,
|
||||
with newer messages of the same priority being placed after
|
||||
older messages with the same priority.
|
||||
|
||||
If the message queue is already full
|
||||
(i.e., the number of messages on the queue equals the queue's
|
||||
.I mq_maxmsg
|
||||
attribute), then, by default,
|
||||
.BR mq_send ()
|
||||
blocks until sufficient space becomes available to allow the message
|
||||
to be queued, or until the call is interrupted by a signal handler.
|
||||
If the
|
||||
.B O_NONBLOCK
|
||||
flag is enabled for the message queue description,
|
||||
then the call instead fails immediately with the error
|
||||
.BR EAGAIN .
|
||||
|
||||
.BR mq_timedsend ()
|
||||
behaves just like
|
||||
.BR mq_send (),
|
||||
except that if the queue is full and the
|
||||
.B O_NONBLOCK
|
||||
flag is not enabled for the message queue description, then
|
||||
.I abs_timeout
|
||||
points to a structure which specifies a ceiling on the time for which
|
||||
the call will block.
|
||||
This ceiling is an absolute timeout in seconds and nanoseconds
|
||||
since the Epoch (midnight on the morning of 1 January 1970),
|
||||
specified in the following structure:
|
||||
.sp
|
||||
.RS
|
||||
.nf
|
||||
struct timespec {
|
||||
time_t tv_sec; /* seconds */
|
||||
long tv_nsec; /* nanoseconds */
|
||||
};
|
||||
|
||||
.fi
|
||||
.RE
|
||||
If the message queue is full,
|
||||
and the timeout has already expired by the time of the call,
|
||||
.BR mq_timedsend ()
|
||||
returns immediately.
|
||||
.SH RETURN VALUE
|
||||
On success,
|
||||
.BR mq_send ()
|
||||
and
|
||||
.BR mq_timedsend ()
|
||||
return zero; on error, \-1 is returned, with
|
||||
.I errno
|
||||
set to indicate the error.
|
||||
.SH ERRORS
|
||||
.TP
|
||||
.B EAGAIN
|
||||
The queue was empty, and the
|
||||
.B O_NONBLOCK
|
||||
flag was set for the message queue description referred to by
|
||||
.IR mqdes .
|
||||
.TP
|
||||
.B EBADF
|
||||
The descriptor specified in
|
||||
.I mqdes
|
||||
was invalid.
|
||||
.TP
|
||||
.B EMSGSIZE
|
||||
.IR msg_len
|
||||
was greater than the
|
||||
.I mq_msgsize
|
||||
attribute of the message queue.
|
||||
.TP
|
||||
.B EINTR
|
||||
The call was interrupted by a signal handler.
|
||||
.TP
|
||||
.B EINVAL
|
||||
The call would have blocked, and
|
||||
.I abs_timeout
|
||||
was invalid, either because
|
||||
.I tv_sec
|
||||
was less than zero, or because
|
||||
.I tv_nsec
|
||||
was less than zero or greater than 1000 million.
|
||||
.TP
|
||||
.B ETIMEDOUT
|
||||
The call timed out before a message could be transferred.
|
||||
.SH CONFORMING TO
|
||||
POSIX.1-2001.
|
||||
.SH "SEE ALSO"
|
||||
.BR mq_close (3),
|
||||
.BR mq_getattr (3),
|
||||
.BR mq_notify (3),
|
||||
.BR mq_open (3),
|
||||
.BR mq_receive (3),
|
||||
.BR mq_unlink (3),
|
||||
.BR mq_overview (7)
|
||||
|
|
@ -0,0 +1,66 @@
|
|||
'\" t
|
||||
.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_UNLINK 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
mq_unlink \- remove a message queue
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <mqueue.h>
|
||||
.sp
|
||||
.BI "mqd_t mq_unlink(const char *" name );
|
||||
.fi
|
||||
.SH DESCRIPTION
|
||||
.BR mq_unlink ()
|
||||
removes the specified message queue
|
||||
.IR name .
|
||||
The message queue name is removed immediately.
|
||||
The queue itself is destroyed once any other processes that have
|
||||
the queue open close their descriptors referring to the queue.
|
||||
.SH RETURN VALUE
|
||||
On success
|
||||
.BR mq_unlink ()
|
||||
returns 0; on error, \-1 is returned, with
|
||||
.I errno
|
||||
set to indicate the error.
|
||||
.SH ERRORS
|
||||
.TP
|
||||
.B EACCES
|
||||
The caller does not have permission to unlink this message queue.
|
||||
.TP
|
||||
.B ENAMETOOLONG
|
||||
.IR name
|
||||
was too long.
|
||||
.TP
|
||||
.B ENOENT
|
||||
There is no message queue with the given
|
||||
.IR name .
|
||||
.SH CONFORMING TO
|
||||
POSIX.1-2001.
|
||||
.SH "SEE ALSO"
|
||||
.BR mq_close (3),
|
||||
.BR mq_getattr (3),
|
||||
.BR mq_notify (3),
|
||||
.BR mq_open (3),
|
||||
.BR mq_receive (3),
|
||||
.BR mq_send (3),
|
||||
.BR mq_overview (7)
|
||||
|
|
@ -0,0 +1,246 @@
|
|||
'\" t
|
||||
.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
.\" preserved on all copies.
|
||||
.\"
|
||||
.\" Permission is granted to copy and distribute modified versions of this
|
||||
.\" manual under the conditions for verbatim copying, provided that the
|
||||
.\" entire resulting derived work is distributed under the terms of a
|
||||
.\" permission notice identical to this one.
|
||||
.\"
|
||||
.\" Since the Linux kernel and libraries are constantly changing, this
|
||||
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
||||
.\" responsibility for errors or omissions, or for damages resulting from
|
||||
.\" the use of the information contained herein.
|
||||
.\"
|
||||
.\" Formatted or processed versions of this manual, if unaccompanied by
|
||||
.\" the source, must acknowledge the copyright and authors of this work.
|
||||
.\"
|
||||
.TH MQ_OVERVIEW 7 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
mq_overview \- Overview of POSIX message queues
|
||||
.SH DESCRIPTION
|
||||
POSIX message queues allow processes to exchange data in
|
||||
the form of messages.
|
||||
Message queues are created and opened using
|
||||
.BR mq_open (3);
|
||||
this function returns a
|
||||
.I message queue descriptor
|
||||
.RI ( mqd_t ),
|
||||
which is used to refer to the open message queue in later calls.
|
||||
Each message queue is identified by a
|
||||
.I name
|
||||
of the form
|
||||
.IR /somename .
|
||||
Two processes can operate on the same queue by passing the same name to
|
||||
.BR mq_open ().
|
||||
|
||||
Messages are transferred to and from a queue using
|
||||
.BR mq_send (3)
|
||||
and
|
||||
.BR mq_receive (3).
|
||||
When a process has finished using the queue, it closes it using
|
||||
.BR mq_close (3),
|
||||
and when the queue is no longer required, it can be deleted using
|
||||
.BR mq_unlink (3).
|
||||
Queue attributes can be retrieved and (in some cases) modified using
|
||||
.BR mq_getattr (3)
|
||||
and
|
||||
.BR mq_setattr (3).
|
||||
A process can request asynchronous notification
|
||||
of the arrival of a message on a previously empty queue using
|
||||
.BR mq_notify (3).
|
||||
|
||||
A message queue descriptor is a reference to an
|
||||
.IR "open message queue description"
|
||||
(cf.
|
||||
.BR open (2)).
|
||||
After a
|
||||
.BR fork (2),
|
||||
a child inherits copies of its parent's message queue descriptors,
|
||||
and these descriptors refer to the same open message queue descriptions
|
||||
as the corresponding descriptors in the parent.
|
||||
Corresponding descriptors in the two processes share the flags
|
||||
.RI ( mq_flags )
|
||||
that are associated with the open message queue description.
|
||||
|
||||
Each message has an associated
|
||||
.IR priority ,
|
||||
and messages are always delivered to the receiving process
|
||||
highest priority first.
|
||||
Message priorities range from 0 (low) to
|
||||
.I sysconf(_SC_MQ_PRIO_MAX)\ -\ 1
|
||||
(high).
|
||||
On Linux,
|
||||
.I sysconf(_SC_MQ_PRIO_MAX)
|
||||
returns 32768, but POSIX.1-2001 only requires
|
||||
an implementation to support priorities in the range 0 to 31;
|
||||
some implementations only provide this range.
|
||||
.SH LINUX SPECIFIC DETAILS
|
||||
.SS Versions
|
||||
POSIX message queues have been supported on Linux since kernel 2.6.6.
|
||||
Glibc support has been provided since version 2.3.4.
|
||||
.SS Kernel configuration
|
||||
Support for POSIX message queues is configurable via the
|
||||
.B CONFIG_POSIX_MQUEUE
|
||||
kernel configuration option.
|
||||
This option is enabled by default.
|
||||
.SS Persistence
|
||||
POSIX message queues have kernel persistence:
|
||||
if not removed by
|
||||
.BR mq_unlink (),
|
||||
a message queue will exist until the system is shut down.
|
||||
.SS Linking
|
||||
Programs using the POSIX message queue API must be compiled with
|
||||
.I cc \-lrt
|
||||
to link against the real-time library,
|
||||
.IR librt .
|
||||
.SS /proc interfaces
|
||||
The following interfaces can be used to limit the amount of
|
||||
kernel memory consumed by POSIX message queues:
|
||||
.TP
|
||||
.I /proc/sys/fs/mqueue/msg_max
|
||||
This file can be used to view and change the ceiling value for the
|
||||
maximum number of messages in a queue.
|
||||
This value acts as a ceiling on the
|
||||
.I attr->mq_maxmsg
|
||||
argument given to
|
||||
.BR mq_open (3).
|
||||
The default and minimum value for
|
||||
.I msg_max
|
||||
is 10; the upper limit is HARD_MAX:
|
||||
.IR "(131072\ /\ sizeof(void\ *))"
|
||||
(32768 on Linux/86).
|
||||
This limit is ignored for privileged processes
|
||||
.RB ( CAP_SYS_RESOURCE ),
|
||||
but the HARD_MAX ceiling is nevertheless imposed.
|
||||
.TP
|
||||
.I /proc/sys/fs/mqueue/msgsize_max
|
||||
This file can be used to view and change the ceiling on the
|
||||
maximum message size.
|
||||
This value acts as a ceiling on the
|
||||
.I attr->mq_msgsize
|
||||
argument given to
|
||||
.BR mq_open (3).
|
||||
The default and minimum value for
|
||||
.I msgsize_max
|
||||
is 8192 bytes; the upper limit is INT_MAX
|
||||
(2147483647 on Linux/86).
|
||||
This limit is ignored for privileged processes
|
||||
.RB ( CAP_SYS_RESOURCE ).
|
||||
.TP
|
||||
.I /proc/sys/fs/mqueue/queues_max
|
||||
This file can be used to view and change the system-wide limit on the
|
||||
number of message queues that can be created.
|
||||
Only privileged processes
|
||||
.RB ( CAP_SYS_RESOURCE )
|
||||
can create new message queues once this limit has been reached.
|
||||
The default value for
|
||||
.I queues_max
|
||||
is 256; it can be changed to any value in the range 0 to INT_MAX.
|
||||
.SS Resource limit
|
||||
The
|
||||
.BR RLIMIT_MSGQUEUE
|
||||
resource limit, which places a limit on the amount of space
|
||||
that can be consumed by all of the message queues
|
||||
belonging to a process's real user ID, is described in
|
||||
.BR getrlimit (2).
|
||||
.SS Mounting the message queue file system
|
||||
On Linux, message queues are created in a virtual file system.
|
||||
(Other implementations may also provide such a feature,
|
||||
but the details are likely to differ.)
|
||||
This file system can be mounted using the following commands:
|
||||
.in +0.25i
|
||||
.nf
|
||||
|
||||
$ mkdir /dev/mqueue
|
||||
$ mount -t mqueue none /dev/mqueue
|
||||
|
||||
.fi
|
||||
.in -0.25i
|
||||
The sticky bit is automatically enabled on the mount directory.
|
||||
|
||||
After the file system has been mounted, the message queues on the system
|
||||
can be viewed and manipulated using the commands usually used for files
|
||||
(e.g.,
|
||||
.BR ls (1)
|
||||
and
|
||||
.BR rm (1)).
|
||||
|
||||
The contents of each file in the directory consist of a single line
|
||||
containing information about the queue:
|
||||
.in +0.25i
|
||||
.nf
|
||||
|
||||
$ ls /dev/mqueue/mymq
|
||||
QSIZE:129 NOTIFY:2 SIGNO:0 NOTIFY_PID:8260
|
||||
$ mount -t mqueue none /dev/mqueue
|
||||
|
||||
.fi
|
||||
.in -0.25i
|
||||
These fields are as follows:
|
||||
.TP
|
||||
.B
|
||||
QSIZE
|
||||
Number of bytes of data in all messages in the queue.
|
||||
.TP
|
||||
.B NOTIFY_PID
|
||||
If this is non-zero, then the process with this PID has used
|
||||
.BR mq_notify (3)
|
||||
to register for asynchronous message notification,
|
||||
and the remaining fields describe how notification occurs.
|
||||
.TP
|
||||
.B NOTIFY
|
||||
Notification method:
|
||||
0 is
|
||||
.BR SIGEV_SIGNAL ;
|
||||
1 is
|
||||
.BR SIGEV_NONE;
|
||||
and
|
||||
2 is
|
||||
.BR SIGEV_THREAD .
|
||||
.TP
|
||||
.B SIGNO
|
||||
Signal number to be used for
|
||||
.BR SIGEV_SIGNAL .
|
||||
.SS Polling message queue descriptors
|
||||
On Linux, a message queue descriptor is actually a file descriptor,
|
||||
and can be monitored using
|
||||
.BR select (2),
|
||||
.BR poll (2),
|
||||
or
|
||||
.BR epoll (4).
|
||||
This is not portable.
|
||||
.SH "CONFORMING TO"
|
||||
POSIX.1-2001.
|
||||
.SH NOTES
|
||||
System V message queues
|
||||
.RB ( msgget (2),
|
||||
.BR msgsnd (2),
|
||||
.BR msgrcv (2),
|
||||
etc.) are an older API for exchanging messages between processes.
|
||||
POSIX message queues provide a better designed interface than
|
||||
System V message queues;
|
||||
on the other hand POSIX message queues are less widely available
|
||||
(especially on older systems) than System V message queues.
|
||||
.SH EXAMPLE
|
||||
An example of the use of various message queue functions is shown in
|
||||
.BR mq_notify (3).
|
||||
.SH "SEE ALSO"
|
||||
.BR getrlimit (2),
|
||||
.BR mq_close (3),
|
||||
.BR mq_getattr (3),
|
||||
.BR mq_notify (3),
|
||||
.BR mq_open (3),
|
||||
.BR mq_receive (3),
|
||||
.BR mq_send (3),
|
||||
.BR mq_unlink (3),
|
||||
.BR poll (2),
|
||||
.BR select (2),
|
||||
.BR epoll (4)
|
||||
.\" FIXME add SEE ALSO refs from System V message queue pages to
|
||||
.\" POSIX message queue pages.
|
||||
Loading…
Reference in New Issue