mq_send, mq_timedsend - send a message to a message queue

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ mq_send(), mq_timedsend()                                                   │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

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 a timespec(3) structure.

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

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.

       EMSGSIZEmsg_len was greater than the mq_msgsize attribute of the message queue.

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

       POSIX.1-2001.

       Real-time library (librt, -lrt)

       mq_send, mq_timedsend - send a message to a message queue

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

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

Linux man-pages 6.9.1                              2024-05-02                                         mq_send(3)

       POSIX.1-2008.

#include<mqueue.h>intmq_send(mqd_tmqdes,constcharmsg_ptr[.msg_len],size_tmsg_len,unsignedintmsg_prio);#include<time.h>#include<mqueue.h>intmq_timedsend(mqd_tmqdes,constcharmsg_ptr[.msg_len],size_tmsg_len,unsignedintmsg_prio,conststructtimespec*abs_timeout);

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

       mq_timedsend():
           _POSIX_C_SOURCE >= 200112L

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