mq_send man page on FreeBSD

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MQ_SEND(2)		    BSD System Calls Manual		    MQ_SEND(2)

NAME
     mq_send, mq_timedsend — send a message to message queue (REALTIME)

LIBRARY
     POSIX Real-time Library (librt, -lrt)

SYNOPSIS
     #include <mqueue.h>

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

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

DESCRIPTION
     The mq_send() system call adds the message pointed to by the argument
     msg_ptr to the message queue specified by mqdes.  The msg_len argument
     specifies the length of the message, in bytes, pointed to by msg_ptr.
     The value of msg_len should be less than or equal to the mq_msgsize
     attribute of the message queue, or mq_send() will fail.

     If the specified message queue is not full, mq_send() will behave as if
     the message is inserted into the message queue at the position indicated
     by the msg_prio argument.	A message with a larger numeric value of
     msg_prio will be inserted before messages with lower values of msg_prio.
     A message will be inserted after other messages in the queue, if any,
     with equal msg_prio.  The value of msg_prio should be less than
     {MQ_PRIO_MAX}.

     If the specified message queue is full and O_NONBLOCK is not set in the
     message queue description associated with mqdes, mq_send() will block
     until space becomes available to enqueue the message, or until mq_send()
     is interrupted by a signal.  If more than one thread is waiting to send
     when space becomes available in the message queue and the Priority Sched‐
     uling option is supported, then the thread of the highest priority that
     has been waiting the longest will be unblocked to send its message.  Oth‐
     erwise, it is unspecified which waiting thread is unblocked.  If the
     specified message queue is full and O_NONBLOCK is set in the message
     queue description associated with mqdes, the message will not be queued
     and mq_send() will return an error.

     The mq_timedsend() system call will add a message to the message queue
     specified by mqdes in the manner defined for the mq_send() system call.
     However, if the specified message queue is full and O_NONBLOCK is not set
     in the message queue description associated with mqdes, the wait for suf‐
     ficient room in the queue will be terminated when the specified timeout
     expires.  If O_NONBLOCK is set in the message queue description, this
     system call is equivalent to mq_send().

     The timeout will expire when the absolute time specified by abs_timeout
     passes, as measured by the clock on which timeouts are based (that is,
     when the value of that clock equals or exceeds abs_timeout), or if the
     absolute time specified by abs_timeout has already been passed at the
     time of the call.

     The timeout is based on the CLOCK_REALTIME clock.

RETURN VALUES
     Upon successful completion, the mq_send() and mq_timedsend() system calls
     return a value of zero.  Otherwise, no message will be enqueued, the sys‐
     tem calls return -1, and the global variable errno is set to indicate the
     error.

ERRORS
     The mq_send() and mq_timedsend() system calls will fail if:

     [EAGAIN]		The O_NONBLOCK flag is set in the message queue
			description associated with mqdes, and the specified
			message queue is full.

     [EBADF]		The mqdes argument is not a valid message queue
			descriptor open for writing.

     [EINTR]		A signal interrupted the call to mq_send() or
			mq_timedsend().

     [EINVAL]		The value of msg_prio was outside the valid range.

     [EINVAL]		The process or thread would have blocked, and the
			abs_timeout parameter specified a nanoseconds field
			value less than zero or greater than or equal to 1000
			million.

     [EMSGSIZE]		The specified message length, msg_len, exceeds the
			message size attribute of the message queue.

     [ETIMEDOUT]	The O_NONBLOCK flag was not set when the message queue
			was opened, but the timeout expired before the message
			could be added to the queue.

SEE ALSO
     mq_open(2), mq_receive(2), mq_setattr(2), mq_timedreceive(2)

STANDARDS
     The mq_send() and mq_timedsend() system calls conform to IEEE Std
     1003.1-2004 (“POSIX.1”).

HISTORY
     Support for POSIX message queues first appeared in FreeBSD 7.0.

COPYRIGHT
     Portions of this text are reprinted and reproduced in electronic form
     from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology
     -- Portable Operating System Interface (POSIX), The Open Group Base Spec‐
     ifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electri‐
     cal and Electronics Engineers, Inc and The Open Group.  In the event of
     any discrepancy between this version and the original IEEE and The Open
     Group Standard, the original IEEE and The Open Group Standard is the ref‐
     eree document.  The original Standard can be obtained online at
	  http://www.opengroup.org/unix/online.html.

BSD			       November 29, 2005			   BSD
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