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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 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  priority  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 handler.  If the O_NONBLOCK flag is enabled for the message queue description, 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 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),
       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 message 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 attributes(7).

       ┌──────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├──────────────────────────┼───────────────┼─────────┤
       │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

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       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.