mq_timedreceive

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
       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 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 5.02 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)