1MQ_SEND(3) Linux Programmer's Manual MQ_SEND(3)
2
6 mq_send, mq_timedsend - send a message to a message queue
7
9 #include <mqueue.h>
10 int mq_send(mqd_t mqdes, const char *msg_ptr,
12 size_t msg_len, unsigned int msg_prio);
13 #include <time.h>
15 #include <mqueue.h>
16 int mq_timedsend(mqd_t mqdes, const char *msg_ptr,
18 size_t msg_len, unsigned int msg_prio,
19 const struct timespec *abs_timeout);
20 Link with -lrt.
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 mq_timedsend():
26 _POSIX_C_SOURCE >= 200112L
27
29 mq_send() adds the message pointed to by msg_ptr to the message queue
30 referred to by the message queue descriptor mqdes. The msg_len argu‐
31 ment specifies the length of the message pointed to by msg_ptr; this
32 length must be less than or equal to the queue's mq_msgsize attribute.
33 Zero-length messages are allowed.
34 The msg_prio argument is a nonnegative integer that specifies the pri‐
36 ority of this message. Messages are placed on the queue in decreasing
37 order of priority, with newer messages of the same priority being
38 placed after older messages with the same priority. See mq_overview(7)
39 for details on the range for the message priority.
40 If the message queue is already full (i.e., the number of messages on
42 the queue equals the queue's mq_maxmsg attribute), then, by default,
43 mq_send() blocks until sufficient space becomes available to allow the
44 message to be queued, or until the call is interrupted by a signal han‐
45 dler. If the O_NONBLOCK flag is enabled for the message queue descrip‐
46 tion, then the call instead fails immediately with the error EAGAIN.
47 mq_timedsend() behaves just like mq_send(), except that if the queue is
49 full and the O_NONBLOCK flag is not enabled for the message queue de‐
50 scription, then abs_timeout points to a structure which specifies how
51 long the call will block. This value is an absolute timeout in seconds
52 and nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), spec‐
53 ified in the following structure:
54 struct timespec {
56 time_t tv_sec; /* seconds */
57 long tv_nsec; /* nanoseconds */
58 };
59 If the message queue is full, and the timeout has already expired by
61 the time of the call, mq_timedsend() returns immediately.
62
64 On success, mq_send() and mq_timedsend() return zero; on error, -1 is
65 returned, with errno set to indicate the error.
66
68 EAGAIN The queue was full, and the O_NONBLOCK flag was set for the mes‐
69 sage queue description referred to by mqdes.
70 EBADF The descriptor specified in mqdes was invalid or not opened for
72 writing.
73 EINTR The call was interrupted by a signal handler; see signal(7).
75 EINVAL The call would have blocked, and abs_timeout was invalid, either
77 because tv_sec was less than zero, or because tv_nsec was less
78 than zero or greater than 1000 million.
79 EMSGSIZE
81 msg_len was greater than the mq_msgsize attribute of the message
82 queue.
83 ETIMEDOUT
85 The call timed out before a message could be transferred.
86
88 For an explanation of the terms used in this section, see at‐
89 tributes(7).
90 ┌────────────────────────────────────────────┬───────────────┬─────────┐
92 │Interface │ Attribute │ Value │
93 ├────────────────────────────────────────────┼───────────────┼─────────┤
94 │mq_send(), mq_timedsend() │ Thread safety │ MT-Safe │
95 └────────────────────────────────────────────┴───────────────┴─────────┘
96
98 POSIX.1-2001, POSIX.1-2008.
99
101 On Linux, mq_timedsend() is a system call, and mq_send() is a library
102 function layered on top of that system call.
103
105 mq_close(3), mq_getattr(3), mq_notify(3), mq_open(3), mq_receive(3),
106 mq_unlink(3), mq_overview(7), time(7)
107
109 This page is part of release 5.13 of the Linux man-pages project. A
110 description of the project, information about reporting bugs, and the
111 latest version of this page, can be found at
112 https://www.kernel.org/doc/man-pages/.
113Linux 2021-03-22 MQ_SEND(3)