man3/mq_send.3

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  23 .TH MQ_SEND 3 2006-02-25 "Linux" "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 .sp
  42 Link with \fI\-lrt\fP.
  43 .SH DESCRIPTION
  44 .BR mq_send ()
  45 adds the message pointed to by
  46 .IR msg_ptr
  47 to the message queue referred to by the descriptor
  48 .IR mqdes .
  49 The
  50 .I msg_len
  51 argument specifies the length of the message pointed to by
  52 .IR msg_ptr ;
  53 this length must be less than or equal to the queue's
  54 .I mq_msgsize
  55 attribute.
  56 Zero-length messages are allowed.
  57
  58 The
  59 .I msg_prio
  60 argument is a non-negative integer that specifies the priority
  61 of this message.
  62 Messages are placed on the queue in decreasing order of priority,
  63 with newer messages of the same priority being placed after
  64 older messages with the same priority.
  65
  66 If the message queue is already full
  67 (i.e., the number of messages on the queue equals the queue's
  68 .I mq_maxmsg
  69 attribute), then, by default,
  70 .BR mq_send ()
  71 blocks until sufficient space becomes available to allow the message
  72 to be queued, or until the call is interrupted by a signal handler.
  73 If the
  74 .B O_NONBLOCK
  75 flag is enabled for the message queue description,
  76 then the call instead fails immediately with the error
  77 .BR EAGAIN .
  78
  79 .BR mq_timedsend ()
  80 behaves just like
  81 .BR mq_send (),
  82 except that if the queue is full and the
  83 .B O_NONBLOCK
  84 flag is not enabled for the message queue description, then
  85 .I abs_timeout
  86 points to a structure which specifies a ceiling on the time for which
  87 the call will block.
  88 This ceiling is an absolute timeout in seconds and nanoseconds
  89 since the Epoch (midnight on the morning of 1 January 1970),
  90 specified in the following structure:
  91 .sp
  92 .RS
  93 .nf
  94 struct timespec {
  95     time_t tv_sec;        /* seconds */
  96     long   tv_nsec;       /* nanoseconds */
  97 };
  98
  99 .fi
 100 .RE
 101 If the message queue is full,
 102 and the timeout has already expired by the time of the call,
 103 .BR mq_timedsend ()
 104 returns immediately.
 105 .SH RETURN VALUE
 106 On success,
 107 .BR mq_send ()
 108 and
 109 .BR mq_timedsend ()
 110 return zero; on error, \-1 is returned, with
 111 .I errno
 112 set to indicate the error.
 113 .SH ERRORS
 114 .TP
 115 .B EAGAIN
 116 The queue was empty, and the
 117 .B O_NONBLOCK
 118 flag was set for the message queue description referred to by
 119 .IR mqdes .
 120 .TP
 121 .B EBADF
 122 The descriptor specified in
 123 .I mqdes
 124 was invalid.
 125 .TP
 126 .B EINTR
 127 The call was interrupted by a signal handler.
 128 .TP
 129 .B EINVAL
 130 The call would have blocked, and
 131 .I abs_timeout
 132 was invalid, either because
 133 .I tv_sec
 134 was less than zero, or because
 135 .I tv_nsec
 136 was less than zero or greater than 1000 million.
 137 .TP
 138 .B EMSGSIZE
 139 .IR msg_len
 140 was greater than the
 141 .I mq_msgsize
 142 attribute of the message queue.
 143 .TP
 144 .B ETIMEDOUT
 145 The call timed out before a message could be transferred.
 146 .SH CONFORMING TO
 147 POSIX.1-2001.
 148 .SH "SEE ALSO"
 149 .BR mq_close (3),
 150 .BR mq_getattr (3),
 151 .BR mq_notify (3),
 152 .BR mq_open (3),
 153 .BR mq_receive (3),
 154 .BR mq_unlink (3),
 155 .BR feature_test_macros (7),
 156 .BR mq_overview (7)