MQ_RECEIVE
Section: Linux Programmer's Manual (3)
Updated: 2010-09-20
NAME
mq_receive, mq_timedreceive - receive a message from a message queue
SYNOPSIS
#include <mqueue.h>
ssize_t mq_receive(mqd_t mqdes, char *msg_ptr,
size_t msg_len, unsigned *msg_prio);
#include <time.h>
#include <mqueue.h>
ssize_t mq_timedreceive(mqd_t mqdes, char *msg_ptr,
size_t msg_len, unsigned *msg_prio,
const struct timespec *abs_timeout);
Link with -lrt.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
mq_timedreceive():
-
_XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L
DESCRIPTION
mq_receive()
removes the oldest message with the highest priority from
the message queue referred to by the descriptor
mqdes,
and places it in the buffer pointed to by
msg_ptr.
The
msg_len
argument specifies the size of the buffer pointed to by
msg_ptr;
this must be greater than the
mq_msgsize
attribute of the queue (see
mq_getattr(3)).
If
prio
is not NULL, then the buffer to which it points is used
to return the priority associated with the received message.
If the queue is empty, then, by default,
mq_receive()
blocks until a message becomes available,
or 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_timedreceive()
behaves just like
mq_receive(),
except that if the queue is empty and the
O_NONBLOCK
flag is not enabled for the message queue description, then
abs_timeout
points to a structure which specifies a ceiling on the time for which
the call will block.
This ceiling is an absolute timeout in seconds and nanoseconds
since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), and it is
specified in the following structure:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
If no message is available,
and the timeout has already expired by the time of the call,
mq_timedreceive()
returns immediately.
RETURN VALUE
On success,
mq_receive()
and
mq_timedreceive()
return the number of bytes in the received message;
on error, -1 is returned, with
errno
set to indicate the error.
ERRORS
- EAGAIN
-
The queue was empty, and the
O_NONBLOCK
flag was set for the message queue description referred to by
mqdes.
- EBADF
-
The descriptor specified in
mqdes
was invalid.
- 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.
- EMSGSIZE
-
msg_len
was less than the
mq_msgsize
attribute of the message queue.
- ETIMEDOUT
-
The call timed out before a message could be transferred.
CONFORMING TO
POSIX.1-2001.
NOTES
On Linux,
mq_timedreceive()
is a system call, and
mq_receive()
is a library function layered on top of that system call.
SEE ALSO
mq_close(3),
mq_getattr(3),
mq_notify(3),
mq_open(3),
mq_send(3),
mq_unlink(3),
feature_test_macros(7),
mq_overview(7),
time(7)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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Time: 07:34:55 GMT, March 26, 2013