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mq_receive(3) — Linux manual page

mq_receive(3) Library Functions Manual mq_receive(3)

NAME top

 mq_receive, mq_timedreceive - receive a message from a message
 queue

LIBRARY top

 Real-time library (librt, -lrt)

SYNOPSIS top

 #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

DESCRIPTION top

 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年01月01日 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.

RETURN VALUE top

 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 top

 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.

ATTRIBUTES top

 For an explanation of the terms used in this section, see
 attributes(7).
 ┌──────────────────────────────────────┬───────────────┬─────────┐
 │ Interface │ Attribute │ Value │
 ├──────────────────────────────────────┼───────────────┼─────────┤
 │ mq_receive(), mq_timedreceive() │ Thread safety │ MT-Safe │
 └──────────────────────────────────────┴───────────────┴─────────┘

VERSIONS top

 On Linux, mq_timedreceive() is a system call, and mq_receive() is
 a library function layered on top of that system call.

STANDARDS top

 POSIX.1-2008.

HISTORY top

 POSIX.1-2001.

SEE ALSO top

 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)

COLOPHON top

 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年02月02日. 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年07月23日 mq_receive(3)

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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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