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 *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.

DESCRIPTION
       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  inter-
       rupted  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,
       1970-01-01 00:00:00 +0000 (UTC), and it is 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 imme-
       diately.

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.

       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.

CONFORMING TO
       POSIX.1-2001.

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),  feature_test_macros(7),  mq_overview(7),
       time(7)

COLOPHON
       This  page  is  part of release 3.25 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                                                      2010-02-25                                              MQ_RECEIVE(3)