.\" Copyright (c) 2005 David Xu .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice(s), this list of conditions and the following disclaimer as .\" the first lines of this file unmodified other than the possible .\" addition of one or more copyright notices. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice(s), this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY .\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE .\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR .\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, .\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE .\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, .\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .Dd November 29, 2005 .Dt MQ_SEND 2 .Os .Sh NAME .Nm mq_send , mq_timedsend .Nd "send a message to message queue (REALTIME)" .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In mqueue.h .Ft int .Fo mq_send .Fa "mqd_t mqdes" .Fa "const char *msg_ptr" .Fa "size_t msg_len" .Fa "unsigned msg_prio" .Fc .Ft int .Fo mq_timesend .Fa "mqd_t mqdes" .Fa "const char *msg_ptr" .Fa "size_t msg_len" .Fa "unsigned msg_prio" .Fa "const struct timespec *abs_timeout" .Fc .Sh DESCRIPTION The .Fn mq_send system call adds the message pointed to by the argument .Fa msg_ptr to the message queue specified by .Fa mqdes . The .Fa msg_len argument specifies the length of the message, in bytes, pointed to by .Fa msg_ptr . The value of .Fa msg_len should be less than or equal to the .Fa mq_msgsize attribute of the message queue, or .Fn mq_send will fail. .Pp If the specified message queue is not full, .Fn mq_send will behave as if the message is inserted into the message queue at the position indicated by the .Fa msg_prio argument. A message with a larger numeric value of .Fa msg_prio will be inserted before messages with lower values of .Fa msg_prio . A message will be inserted after other messages in the queue, if any, with equal .Fa msg_prio . The value of .Fa msg_prio should be less than .Brq Dv MQ_PRIO_MAX . .Pp If the specified message queue is full and .Dv O_NONBLOCK is not set in the message queue description associated with .Fa mqdes , .Fn mq_send will block until space becomes available to enqueue the message, or until .Fn 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 Scheduling option is supported, then the thread of the highest priority that has been waiting the longest will be unblocked to send its message. Otherwise, it is unspecified which waiting thread is unblocked. If the specified message queue is full and .Dv O_NONBLOCK is set in the message queue description associated with .Fa mqdes , the message will not be queued and .Fn mq_send will return an error. .Pp The .Fn mq_timedsend system call will add a message to the message queue specified by .Fa mqdes in the manner defined for the .Fn mq_send system call. However, if the specified message queue is full and .Dv O_NONBLOCK is not set in the message queue description associated with .Fa mqdes , the wait for sufficient room in the queue will be terminated when the specified timeout expires. If .Dv O_NONBLOCK is set in the message queue description, this system call is equivalent to .Fn mq_send . .Pp The timeout will expire when the absolute time specified by .Fa abs_timeout passes, as measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds .Fa abs_timeout ) , or if the absolute time specified by .Fa abs_timeout has already been passed at the time of the call. .Pp The timeout is based on the CLOCK_REALTIME clock. .Sh RETURN VALUES Upon successful completion, the .Fn mq_send and .Fn mq_timedsend system calls return a value of zero. Otherwise, no message will be enqueued, the system calls return -1, and .Va errno is set to indicate the error. .Sh ERRORS The .Fn mq_send and .Fn mq_timedsend system calls will fail if: .Bl -tag -width Er .It Bq Er EAGAIN The .Dv O_NONBLOCK flag is set in the message queue description associated with .Fa mqdes , and the specified message queue is full. .It Bq Er EBADF The .Fa mqdes argument is not a valid message queue descriptor open for writing. .It Bq Er EINTR A signal interrupted the call to .Fn mq_send or .Fn mq_timedsend. .It Bq Er EINVAL The value of .Fa msg_prio was outside the valid range. .It Bq Er EINVAL The process or thread would have blocked, and the .Fa abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million. .It Bq Er EMSGSIZE The specified message length, .Fa msg_len , exceeds the message size attribute of the message queue. .It Bq Er ETIMEDOUT The .Dv 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. .El .Sh SEE ALSO .Xr mq_open 2 , .Xr mq_receive 2 , .Xr mq_setattr 2 , .Xr mq_timereceive 2 .Sh STANDARDS The .Fn mq_send and .Fn mq_timesend system calls conform to .St -p1003.1-2004 . .Sh HISTORY Support for POSIX message queue first appeared in .Fx 7.0 .