NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON
MQ_RECEIVE(3) Linux Programmer's Manual MQ_RECEIVE(3)
mq_receive, mq_timedreceive - receive a message from a message queue
#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.
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 (midnight 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.
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.
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.
POSIX.1-2001.
On Linux, mq_timedreceive() is a system call, and mq_receive() is a library
function layered on top of that system call.
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)
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)