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man:mq_receive

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 int *msg_prio);
     #include <time.h>
     #include <mqueue.h>
     ssize_t mq_timedreceive(mqd_t mqdes, char *msg_ptr,
                        size_t msg_len, unsigned int *msg_prio,
                        const struct timespec *abs_timeout);
     Link with -lrt.
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     mq_timedreceive():
         _POSIX_C_SOURCE >= 200112L

DESCRIPTION

     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 argu-
     ment 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 mes-
     sage.
     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 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 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 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

     For  an  explanation  of  the  terms  used   in   this   section,   see
     attributes(7).
     +--------------------------------+---------------+---------+
     |Interface                       | Attribute     | Value   |
     +--------------------------------+---------------+---------+
     |mq_receive(), mq_timedreceive() | Thread safety | MT-Safe |
     +--------------------------------+---------------+---------+

CONFORMING TO

     POSIX.1-2001, POSIX.1-2008.

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), mq_overview(7), time(7)

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 MQ_RECEIVE(3)

/data/webs/external/dokuwiki/data/pages/man/mq_receive.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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