mq_send

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():
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       mq_send()  adds  the message pointed to by msg_ptr to the message queue
       referred to by the message queue descriptor mqdes.  The  msg_len  argu-
       ment  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.  See mq_overview(7)
       for details on the range for the message 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 de-
       scription, then abs_timeout points to a structure which  specifies  how
       long the call will block.  This value is an absolute timeout in seconds
       and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), spec-
       ified 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 or not opened  for
              writing.

       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
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +--------------------------+---------------+---------+
       |Interface                 | Attribute     | Value   |
       +--------------------------+---------------+---------+
       |mq_send(), mq_timedsend() | Thread safety | MT-Safe |
       +--------------------------+---------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

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 5.05 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
       https://www.kernel.org/doc/man-pages/.

Linux                             2017-09-15                        MQ_SEND(3)