mq_send(3)



MQ_SEND(3)                 Linux Programmer's Manual                MQ_SEND(3)

NAME
       mq_send, mq_timedsend - send a message to a message queue

SYNOPSIS
       #include <mqueue.h>

       int mq_send(mqd_t mqdes, const char *msg_ptr,
                     size_t msg_len, unsigned int msg_prio);

       #include <time.h>
       #include <mqueue.h>

       int mq_timedsend(mqd_t mqdes, const char *msg_ptr,
                     size_t msg_len, unsigned int msg_prio,
                     const struct timespec *abs_timeout);

       Link with -lrt.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       mq_timedsend():
           _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       mq_send()  adds  the message pointed to by msg_ptr to the message queue
       referred to by the descriptor mqdes.  The  msg_len  argument  specifies
       the  length  of  the message pointed to by msg_ptr; this length must be
       less than or equal to the queue's  mq_msgsize  attribute.   Zero-length
       messages are allowed.

       The  msg_prio argument is a nonnegative integer that specifies the pri-
       ority 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 mq_maxmsg attribute), then, by default,
       mq_send() blocks until sufficient space becomes available to allow  the
       message to be queued, or until the call is interrupted by a signal han-
       dler.  If the O_NONBLOCK flag is enabled for the message queue descrip-
       tion, then the call instead fails immediately with the error EAGAIN.

       mq_timedsend() behaves just like mq_send(), except that if the queue is
       full and the O_NONBLOCK flag is  not  enabled  for  the  message  queue
       description,  then  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, 1970-01-01
       00:00:00 +0000 (UTC), and it is specified in the following structure:

           struct timespec {
               time_t tv_sec;        /* seconds */
               long   tv_nsec;       /* nanoseconds */
           };

       If the message queue is full, and the timeout has  already  expired  by
       the time of the call, mq_timedsend() returns immediately.

RETURN VALUE
       On  success,  mq_send() and mq_timedsend() return zero; on error, -1 is
       returned, with errno set to indicate the error.

ERRORS
       EAGAIN The queue was full, and the O_NONBLOCK flag was set for the mes-
              sage queue description referred to by mqdes.

       EBADF  The descriptor specified in mqdes was invalid.

       EINTR  The call was interrupted by a signal handler; see signal(7).

       EINVAL The call would have blocked, and abs_timeout was invalid, either
              because tv_sec was less than zero, or because tv_nsec  was  less
              than zero or greater than 1000 million.

       EMSGSIZE
              msg_len was greater than the mq_msgsize attribute of the message
              queue.

       ETIMEDOUT
              The call timed out before a message could be transferred.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The mq_send() and mq_timedsend() functions are thread-safe.

CONFORMING TO
       POSIX.1-2001.

NOTES
       On Linux, mq_timedsend() is a system call, and mq_send() is  a  library
       function layered on top of that system call.

SEE ALSO
       mq_close(3),  mq_getattr(3),  mq_notify(3),  mq_open(3), mq_receive(3),
       mq_unlink(3), mq_overview(7), time(7)

COLOPHON
       This page is part of release 3.74 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       http://www.kernel.org/doc/man-pages/.

Linux                             2014-06-03                        MQ_SEND(3)

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