man3/mq_send.3

   1 '\" t
   2 .\" Hey Emacs! This file is -*- nroff -*- source.
   3 .\"
   4 .\" Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
   5 .\"
   6 .\" Permission is granted to make and distribute verbatim copies of this
   7 .\" manual provided the copyright notice and this permission notice are
   8 .\" preserved on all copies.
   9 .\"
  10 .\" Permission is granted to copy and distribute modified versions of this
  11 .\" manual under the conditions for verbatim copying, provided that the
  12 .\" entire resulting derived work is distributed under the terms of a
  13 .\" permission notice identical to this one.
  14 .\"
  15 .\" Since the Linux kernel and libraries are constantly changing, this
  16 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  17 .\" responsibility for errors or omissions, or for damages resulting from
  18 .\" the use of the information contained herein.
  19 .\"
  20 .\" Formatted or processed versions of this manual, if unaccompanied by
  21 .\" the source, must acknowledge the copyright and authors of this work.
  22 .\"
  23 .TH MQ_SEND 3 2006-02-25 "Linux 2.6.16" "Linux Programmer's Manual"
  24 .SH NAME
  25 mq_send, mq_timedsend \- send a message to a message queue
  26 .SH SYNOPSIS
  27 .nf
  28 .B #include <mqueue.h>
  29 .sp
  30 .BI "mqd_t mq_send(mqd_t " mqdes ", const char *" msg_ptr ,
  31 .BI "              size_t " msg_len ", unsigned " msg_prio );
  32 .sp
  33 .B #define _XOPEN_SOURCE 600
  34 .B #include <time.h>
  35 .B #include <mqueue.h>
  36 .sp
  37 .BI "mqd_t mq_timedsend(mqd_t " mqdes ", const char *" msg_ptr ,
  38 .BI "              size_t " msg_len ", unsigned " msg_prio ,
  39 .BI "              const struct timespec *" abs_timeout );
  40 .fi
  41 .SH DESCRIPTION
  42 .BR mq_send ()
  43 adds the message pointed to by
  44 .IR msg_ptr
  45 to the message queue referred to by the descriptor
  46 .IR mqdes .
  47 The
  48 .I msg_len
  49 argument specifies the length of the message pointed to by
  50 .IR msg_ptr ;
  51 this length must be less than or equal to the queue's
  52 .I mq_msgsize
  53 attribute.
  54 Zero-length messages are allowed.
  55
  56 The
  57 .I msg_prio
  58 argument is a non-negative integer that specifies the priority
  59 of this message.
  60 Messages are placed on the queue in decreasing order of priority,
  61 with newer messages of the same priority being placed after
  62 older messages with the same priority.
  63
  64 If the message queue is already full
  65 (i.e., the number of messages on the queue equals the queue's
  66 .I mq_maxmsg
  67 attribute), then, by default,
  68 .BR mq_send ()
  69 blocks until sufficient space becomes available to allow the message
  70 to be queued, or until the call is interrupted by a signal handler.
  71 If the
  72 .B O_NONBLOCK
  73 flag is enabled for the message queue description,
  74 then the call instead fails immediately with the error
  75 .BR EAGAIN .
  76
  77 .BR mq_timedsend ()
  78 behaves just like
  79 .BR mq_send (),
  80 except that if the queue is full and the
  81 .B O_NONBLOCK
  82 flag is not enabled for the message queue description, then
  83 .I abs_timeout
  84 points to a structure which specifies a ceiling on the time for which
  85 the call will block.
  86 This ceiling is an absolute timeout in seconds and nanoseconds
  87 since the Epoch (midnight on the morning of 1 January 1970),
  88 specified in the following structure:
  89 .sp
  90 .RS
  91 .nf
  92 struct timespec {
  93     time_t tv_sec;        /* seconds */
  94     long   tv_nsec;       /* nanoseconds */
  95 };
  96
  97 .fi
  98 .RE
  99 If the message queue is full,
 100 and the timeout has already expired by the time of the call,
 101 .BR mq_timedsend ()
 102 returns immediately.
 103 .SH RETURN VALUE
 104 On success,
 105 .BR mq_send ()
 106 and
 107 .BR mq_timedsend ()
 108 return zero; on error, \-1 is returned, with
 109 .I errno
 110 set to indicate the error.
 111 .SH ERRORS
 112 .TP
 113 .B EAGAIN
 114 The queue was empty, and the
 115 .B O_NONBLOCK
 116 flag was set for the message queue description referred to by
 117 .IR mqdes .
 118 .TP
 119 .B EBADF
 120 The descriptor specified in
 121 .I mqdes
 122 was invalid.
 123 .TP
 124 .B EMSGSIZE
 125 .IR msg_len
 126 was greater than the
 127 .I mq_msgsize
 128 attribute of the message queue.
 129 .TP
 130 .B EINTR
 131 The call was interrupted by a signal handler.
 132 .TP
 133 .B EINVAL
 134 The call would have blocked, and
 135 .I abs_timeout
 136 was invalid, either because
 137 .I tv_sec
 138 was less than zero, or because
 139 .I tv_nsec
 140 was less than zero or greater than 1000 million.
 141 .TP
 142 .B ETIMEDOUT
 143 The call timed out before a message could be transferred.
 144 .SH CONFORMING TO
 145 POSIX.1-2001.
 146 .SH "SEE ALSO"
 147 .BR mq_close (3),
 148 .BR mq_getattr (3),
 149 .BR mq_notify (3),
 150 .BR mq_open (3),
 151 .BR mq_receive (3),
 152 .BR mq_unlink (3),
 153 .BR feature_test_macros (7),
 154 .BR mq_overview (7)