2006-03-01 03:21:20 +00:00
|
|
|
'\" 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.\" manual page may be incorrect or out-of-date.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
|
2006-09-15 11:17:36 +00:00
|
|
|
.BI "ssize_t mq_receive(mqd_t " mqdes ", char *" msg_ptr ,
|
|
|
|
.BI " size_t " msg_len ", unsigned *" msg_prio );
|
2006-03-01 03:21:20 +00:00
|
|
|
.sp
|
|
|
|
.B #define _XOPEN_SOURCE 600
|
|
|
|
.B #include <time.h>
|
|
|
|
.B #include <mqueue.h>
|
|
|
|
.sp
|
2006-09-15 11:17:36 +00:00
|
|
|
.BI "ssize_t mq_timedreceive(mqd_t " mqdes ", char *" msg_ptr ,
|
|
|
|
.BI " size_t " msg_len ", unsigned *" msg_prio ,
|
|
|
|
.BI " const struct timespec *" abs_timeout );
|
2006-03-01 03:21:20 +00:00
|
|
|
.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)
|