mq_timedreceive(3)

1mq_receive(3)              Library Functions 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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LIBRARY

9       Real-time library (librt, -lrt)
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SYNOPSIS

12       #include <mqueue.h>
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14       ssize_t mq_receive(mqd_t mqdes, char msg_ptr[.msg_len],
15                          size_t msg_len, unsigned int *msg_prio);
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17       #include <time.h>
18       #include <mqueue.h>
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20       ssize_t mq_timedreceive(mqd_t mqdes, char *restrict msg_ptr[.msg_len],
21                          size_t msg_len, unsigned int *restrict msg_prio,
22                          const struct timespec *restrict abs_timeout);
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24   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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26       mq_timedreceive():
27           _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

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

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

60       EAGAIN The queue was empty, and the O_NONBLOCK flag was set for the
61              message queue description referred to by mqdes.
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63       EBADF  The descriptor specified in mqdes was invalid or not opened for
64              reading.
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66       EINTR  The call was interrupted by a signal handler; see signal(7).
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68       EINVAL The call would have blocked, and abs_timeout was invalid, either
69              because tv_sec was less than zero, or because tv_nsec was less
70              than zero or greater than 1000 million.
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72       EMSGSIZE
73              msg_len was less than the mq_msgsize attribute of the message
74              queue.
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76       ETIMEDOUT
77              The call timed out before a message could be transferred.
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ATTRIBUTES

80       For an explanation of the terms used in this section, see at‐
81       tributes(7).
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83       ┌────────────────────────────────────────────┬───────────────┬─────────┐
84       │Interface                                   │ Attribute     │ Value   │
85       ├────────────────────────────────────────────┼───────────────┼─────────┤
86       │mq_receive(), mq_timedreceive()             │ Thread safety │ MT-Safe │
87       └────────────────────────────────────────────┴───────────────┴─────────┘
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VERSIONS

90       On Linux, mq_timedreceive() is a system call, and mq_receive() is a li‐
91       brary function layered on top of that system call.
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STANDARDS

94       POSIX.1-2008.
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HISTORY

97       POSIX.1-2001.
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