man3/mq_send.3

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  26 .TH MQ_SEND 3 2015-08-08 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 mq_send, mq_timedsend \- send a message to a message queue
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <mqueue.h>
  32 .sp
  33 .BI "int mq_send(mqd_t " mqdes ", const char *" msg_ptr ,
  34 .BI "              size_t " msg_len ", unsigned int " msg_prio );
  35 .sp
  36 .B #include <time.h>
  37 .B #include <mqueue.h>
  38 .sp
  39 .BI "int mq_timedsend(mqd_t " mqdes ", const char *" msg_ptr ,
  40 .BI "              size_t " msg_len ", unsigned int " msg_prio ,
  41 .BI "              const struct timespec *" abs_timeout );
  42 .fi
  43 .sp
  44 Link with \fI\-lrt\fP.
  45 .sp
  46 .ad l
  47 .in -4n
  48 Feature Test Macro Requirements for glibc (see
  49 .BR feature_test_macros (7)):
  50 .in
  51 .sp
  52 .BR mq_timedsend ():
  53 .RS 4
  54 _XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
  55 .RE
  56 .ad
  57 .SH DESCRIPTION
  58 .BR mq_send ()
  59 adds the message pointed to by
  60 .I msg_ptr
  61 to the message queue referred to by the descriptor
  62 .IR mqdes .
  63 The
  64 .I msg_len
  65 argument specifies the length of the message pointed to by
  66 .IR msg_ptr ;
  67 this length must be less than or equal to the queue's
  68 .I mq_msgsize
  69 attribute.
  70 Zero-length messages are allowed.
  71
  72 The
  73 .I msg_prio
  74 argument is a nonnegative integer that specifies the priority
  75 of this message.
  76 Messages are placed on the queue in decreasing order of priority,
  77 with newer messages of the same priority being placed after
  78 older messages with the same priority.
  79
  80 If the message queue is already full
  81 (i.e., the number of messages on the queue equals the queue's
  82 .I mq_maxmsg
  83 attribute), then, by default,
  84 .BR mq_send ()
  85 blocks until sufficient space becomes available to allow the message
  86 to be queued, or until the call is interrupted by a signal handler.
  87 If the
  88 .B O_NONBLOCK
  89 flag is enabled for the message queue description,
  90 then the call instead fails immediately with the error
  91 .BR EAGAIN .
  92
  93 .BR mq_timedsend ()
  94 behaves just like
  95 .BR mq_send (),
  96 except that if the queue is full and the
  97 .B O_NONBLOCK
  98 flag is not enabled for the message queue description, then
  99 .I abs_timeout
 100 points to a structure which specifies how long the call will block.
 101 This value is an absolute timeout in seconds and nanoseconds
 102 since the Epoch, 1970-01-01 00:00:00 +0000 (UTC),
 103 specified in the following structure:
 104 .sp
 105 .in +4n
 106 .nf
 107 struct timespec {
 108     time_t tv_sec;        /* seconds */
 109     long   tv_nsec;       /* nanoseconds */
 110 };
 111
 112 .fi
 113 .in
 114 If the message queue is full,
 115 and the timeout has already expired by the time of the call,
 116 .BR mq_timedsend ()
 117 returns immediately.
 118 .SH RETURN VALUE
 119 On success,
 120 .BR mq_send ()
 121 and
 122 .BR mq_timedsend ()
 123 return zero; on error, \-1 is returned, with
 124 .I errno
 125 set to indicate the error.
 126 .SH ERRORS
 127 .TP
 128 .B EAGAIN
 129 The queue was full, and the
 130 .B O_NONBLOCK
 131 flag was set for the message queue description referred to by
 132 .IR mqdes .
 133 .TP
 134 .B EBADF
 135 The descriptor specified in
 136 .I mqdes
 137 was invalid.
 138 .TP
 139 .B EINTR
 140 The call was interrupted by a signal handler; see
 141 .BR signal (7).
 142 .TP
 143 .B EINVAL
 144 The call would have blocked, and
 145 .I abs_timeout
 146 was invalid, either because
 147 .I tv_sec
 148 was less than zero, or because
 149 .I tv_nsec
 150 was less than zero or greater than 1000 million.
 151 .TP
 152 .B EMSGSIZE
 153 .I msg_len
 154 was greater than the
 155 .I mq_msgsize
 156 attribute of the message queue.
 157 .TP
 158 .B ETIMEDOUT
 159 The call timed out before a message could be transferred.
 160 .SH ATTRIBUTES
 161 For an explanation of the terms used in this section, see
 162 .BR attributes (7).
 163 .TS
 164 allbox;
 165 lbw25 lb lb
 166 l l l.
 167 Interface       Attribute       Value
 168 T{
 169 .BR mq_send (),
 170 .BR mq_timedsend ()
 171 T}      Thread safety   MT-Safe
 172 .TE
 173 .SH CONFORMING TO
 174 POSIX.1-2001, POSIX.1-2008.
 175 .SH NOTES
 176 On Linux,
 177 .BR mq_timedsend ()
 178 is a system call, and
 179 .BR mq_send ()
 180 is a library function layered on top of that system call.
 181 .SH SEE ALSO
 182 .BR mq_close (3),
 183 .BR mq_getattr (3),
 184 .BR mq_notify (3),
 185 .BR mq_open (3),
 186 .BR mq_receive (3),
 187 .BR mq_unlink (3),
 188 .BR mq_overview (7),
 189 .BR time (7)