mq_timedreceive(3)

1MQ_RECEIVE(3)              Linux Programmer's Manual             MQ_RECEIVE(3)
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NAME

6       mq_receive, mq_timedreceive - receive a message from a message queue
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SYNOPSIS

9       #include <mqueue.h>
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11       ssize_t mq_receive(mqd_t mqdes, char *msg_ptr,
12                          size_t msg_len, unsigned *msg_prio);
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14       #include <time.h>
15       #include <mqueue.h>
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17       ssize_t mq_timedreceive(mqd_t mqdes, char *msg_ptr,
18                          size_t msg_len, unsigned *msg_prio,
19                          const struct timespec *abs_timeout);
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21       Link with -lrt.
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23   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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25       mq_timedreceive():
26           _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

29       mq_receive()  removes the oldest message with the highest priority from
30       the message queue referred to by the descriptor mqdes, and places it in
31       the  buffer  pointed to by msg_ptr.  The msg_len argument specifies the
32       size of the buffer pointed to by msg_ptr; this must be greater than the
33       mq_msgsize  attribute of the queue (see mq_getattr(3)).  If msg_prio is
34       not NULL, then the buffer to which it points is used to return the pri‐
35       ority associated with the received message.
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37       If  the  queue  is empty, then, by default, mq_receive() blocks until a
38       message becomes available, or the call is interrupted by a signal  han‐
39       dler.  If the O_NONBLOCK flag is enabled for the message queue descrip‐
40       tion, then the call instead fails immediately with the error EAGAIN.
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42       mq_timedreceive() behaves just like mq_receive(), except  that  if  the
43       queue  is  empty and the O_NONBLOCK flag is not enabled for the message
44       queue description, then abs_timeout points to a structure which  speci‐
45       fies a ceiling on the time for which the call will block.  This ceiling
46       is an absolute timeout in seconds  and  nanoseconds  since  the  Epoch,
47       1970-01-01  00:00:00  +0000 (UTC), and it is specified in the following
48       structure:
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50           struct timespec {
51               time_t tv_sec;        /* seconds */
52               long   tv_nsec;       /* nanoseconds */
53           };
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55       If no message is available, and the timeout has already expired by  the
56       time of the call, mq_timedreceive() returns immediately.
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RETURN VALUE

59       On  success,  mq_receive()  and  mq_timedreceive() return the number of
60       bytes in the received message; on error, -1 is returned, with errno set
61       to indicate the error.
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ERRORS

64       EAGAIN The  queue  was  empty,  and the O_NONBLOCK flag was set for the
65              message queue description referred to by mqdes.
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67       EBADF  The descriptor specified in mqdes was invalid.
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69       EINTR  The call was interrupted by a signal handler; see signal(7).
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71       EINVAL The call would have blocked, and abs_timeout was invalid, either
72              because  tv_sec  was less than zero, or because tv_nsec was less
73              than zero or greater than 1000 million.
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75       EMSGSIZE
76              msg_len was less than the mq_msgsize attribute  of  the  message
77              queue.
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79       ETIMEDOUT
80              The call timed out before a message could be transferred.
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CONFORMING TO

83       POSIX.1-2001.
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NOTES

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

94       This  page  is  part of release 3.53 of the Linux man-pages project.  A
95       description of the project, and information about reporting  bugs,  can
96       be found at http://www.kernel.org/doc/man-pages/.
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100Linux                             2010-09-20                     MQ_RECEIVE(3)