1MQ_RECEIVE(3) Linux Programmer's Manual MQ_RECEIVE(3)
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6 mq_receive, mq_timedreceive - receive a message from a message queue
7
9 #include <mqueue.h>
10 ssize_t mq_receive(mqd_t mqdes, char *msg_ptr,
12 size_t msg_len, unsigned int *msg_prio);
13 #include <time.h>
15 #include <mqueue.h>
16 ssize_t mq_timedreceive(mqd_t mqdes, char *restrict msg_ptr,
18 size_t msg_len, unsigned int *restrict msg_prio,
19 const struct timespec *restrict abs_timeout);
20 Link with -lrt.
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 mq_timedreceive():
26 _POSIX_C_SOURCE >= 200112L
27
29 mq_receive() removes the oldest message with the highest priority from
30 the message queue referred to by the message queue descriptor mqdes,
31 and places it in the buffer pointed to by msg_ptr. The msg_len argu‐
32 ment specifies the size of the buffer pointed to by msg_ptr; this must
33 be greater than or equal to the mq_msgsize attribute of the queue (see
34 mq_getattr(3)). If msg_prio is not NULL, then the buffer to which it
35 points is used to return the priority associated with the received mes‐
36 sage.
37 If the queue is empty, then, by default, mq_receive() blocks until a
39 message becomes available, or the call is interrupted by a signal han‐
40 dler. If the O_NONBLOCK flag is enabled for the message queue descrip‐
41 tion, then the call instead fails immediately with the error EAGAIN.
42 mq_timedreceive() behaves just like mq_receive(), except that if the
44 queue is empty and the O_NONBLOCK flag is not enabled for the message
45 queue description, then abs_timeout points to a structure which speci‐
46 fies how long the call will block. This value is an absolute timeout
47 in seconds and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000
48 (UTC), specified in the following structure:
49 struct timespec {
51 time_t tv_sec; /* seconds */
52 long tv_nsec; /* nanoseconds */
53 };
54 If no message is available, and the timeout has already expired by the
56 time of the call, mq_timedreceive() returns immediately.
57
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.
62
64 EAGAIN The queue was empty, and the O_NONBLOCK flag was set for the
65 message queue description referred to by mqdes.
66 EBADF The descriptor specified in mqdes was invalid or not opened for
68 reading.
69 EINTR The call was interrupted by a signal handler; see signal(7).
71 EINVAL The call would have blocked, and abs_timeout was invalid, either
73 because tv_sec was less than zero, or because tv_nsec was less
74 than zero or greater than 1000 million.
75 EMSGSIZE
77 msg_len was less than the mq_msgsize attribute of the message
78 queue.
79 ETIMEDOUT
81 The call timed out before a message could be transferred.
82
84 For an explanation of the terms used in this section, see at‐
85 tributes(7).
86 ┌────────────────────────────────────────────┬───────────────┬─────────┐
88 │Interface │ Attribute │ Value │
89 ├────────────────────────────────────────────┼───────────────┼─────────┤
90 │mq_receive(), mq_timedreceive() │ Thread safety │ MT-Safe │
91 └────────────────────────────────────────────┴───────────────┴─────────┘
92
94 POSIX.1-2001, POSIX.1-2008.
95
97 On Linux, mq_timedreceive() is a system call, and mq_receive() is a li‐
98 brary function layered on top of that system call.
99
101 mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_send(3),
102 mq_unlink(3), mq_overview(7), time(7)
103
105 This page is part of release 5.12 of the Linux man-pages project. A
106 description of the project, information about reporting bugs, and the
107 latest version of this page, can be found at
108 https://www.kernel.org/doc/man-pages/.
109Linux 2021-03-22 MQ_RECEIVE(3)