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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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mq_receive(3) Library Functions Manual mq_receive(3)
mq_receive, mq_timedreceive - receive a message from a message
queue
Real-time library (librt, -lrt)
#include <mqueue.h>
ssize_t mq_receive(mqd_t mqdes, char msg_ptr[.msg_len],
size_t msg_len, unsigned int *msg_prio);
#include <time.h>
#include <mqueue.h>
ssize_t mq_timedreceive(mqd_t mqdes, char *restrict msg_ptr[.msg_len],
size_t msg_len, unsigned int *restrict msg_prio,
const struct timespec *restrict abs_timeout);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
mq_timedreceive():
_POSIX_C_SOURCE >= 200112L
mq_receive() removes the oldest message with the highest priority
from the message queue referred to by the message queue 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 or equal to the mq_msgsize
attribute of the queue (see mq_getattr(3)). If msg_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 how long the call will block. This value is an
absolute timeout in seconds and nanoseconds since the Epoch,
1970-01-01 00:00:00 +0000 (UTC), specified in a timespec(3)
structure.
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 or not opened
for reading.
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.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ mq_receive(), mq_timedreceive() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
On Linux, mq_timedreceive() is a system call, and mq_receive() is
a library function layered on top of that system call.
POSIX.1-2008.
POSIX.1-2001.
mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_send(3),
mq_unlink(3), timespec(3), mq_overview(7), time(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.10 2024-07-23 mq_receive(3)
Pages that refer to this page: syscalls(2), mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_send(3), mq_unlink(3), mq_overview(7), signal(7)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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