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MQ_SEND(2) | 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¶
Themq_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 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
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 sufficient 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, themq_send
() and
mq_timedsend
() system calls return a value
of zero. Otherwise, no message will be enqueued, the system calls return -1,
and the global variable errno is set to
indicate the error.
ERRORS¶
Themq_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
() ormq_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¶
Themq_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 Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of Electrical 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 referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html.November 29, 2005 | Debian |