MQ_RECEIVE(3) Linux Programmer's Manual MQ_RECEIVE(3)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);
#define _XOPEN_SOURCE 600
#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.
DESCRIPTIONmq_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 han‐
dler. If the O_NONBLOCK flag is enabled for the message queue descrip‐
tion, 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 speci‐
fies a ceiling on the time for which the call will block. This ceiling
is an absolute timeout in seconds and nanoseconds since the Epoch (mid‐
night on the morning of 1 January 1970), 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 ALSOmq_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 3.23 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/.
Linux 2008-09-29 MQ_RECEIVE(3)
