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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
     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), 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
     attributes(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.