NAME
mq_send — send a message to a message queue
SYNOPSIS
#include <sys/mqueue.h>
int mq_send(mqd_t mqdes,
const char *msg_ptr,
size_t msg_len,
unsigned int msg_prio
);
DESCRIPTION
The
mq_send()
system call adds a 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. 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 insert the message into the queue at the position indicated by the
msg_prio
argument. A message with priority,
msg_prio,
will be inserted behind any other messages with larger or equal priority.
The value of
msg_prio
should be less than
MQ_PRIO_MAX.
If the specified message queue is full and the
O_NONBLOCK
flag is not set in the
message queue blocking status associated with
mqdes,
mq_send()
will block in priority order, until it can send a message on the queue, or
until
mq_send()
is interrupted by a signal.
If the specified message queue is full and the
O_NONBLOCK
flag is set in the message
queue blocking status associated with
mqdes,
the message will not be enqueued, and
mq_send()
will return with an error.
To use this function, link in the realtime library by specifying
-lrt
on the compiler or linker command line.
RETURN VALUE
mq_send()
returns the following values:
- 0
Successful completion. The message is enqueued.
- -1
Failure.
errno
is set to indicate the error and the message is not enqueued.
ERRORS
If
mq_send()
fails,
errno
is set to one of the following values:
- [EAGAIN]
The
O_NONBLOCK
flag is set in the message queue blocking status associated with
mqdes,
and the message queue is full.
- [EBADF]
mqdes
is not a valid message queue descriptor open for writing.
- [EINTR]
A signal interrupted the call to
mq_send().
- [EINVAL]
msg_ptr
points to an invalid address, or the value of
msg_prio
is outside the valid range.
- [EMSGSIZE]
The specified message length,
msg_len,
exceeds the message size attribute of the message queue.
- [ENOSYS]
mq_send()
is not supported by the implementation.
STANDARDS CONFORMANCE
mq_send(): POSIX 1003.1b
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