1MQ_SEND(3P) POSIX Programmer's Manual MQ_SEND(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 mq_send, mq_timedsend — send a message to a message queue (REALTIME)
13
15 #include <mqueue.h>
16 int mq_send(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
18 unsigned msg_prio);
19 #include <mqueue.h>
21 #include <time.h>
22 int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
24 unsigned msg_prio, const struct timespec *abstime);
25
27 The mq_send() function shall add the message pointed to by the argument
28 msg_ptr to the message queue specified by mqdes. The msg_len argument
29 specifies the length of the message, in bytes, pointed to by msg_ptr.
30 The value of msg_len shall be less than or equal to the mq_msgsize
31 attribute of the message queue, or mq_send() shall fail.
32 If the specified message queue is not full, mq_send() shall behave as
34 if the message is inserted into the message queue at the position indi‐
35 cated by the msg_prio argument. A message with a larger numeric value
36 of msg_prio shall be inserted before messages with lower values of
37 msg_prio. A message shall be inserted after other messages in the
38 queue, if any, with equal msg_prio. The value of msg_prio shall be
39 less than {MQ_PRIO_MAX}.
40 If the specified message queue is full and O_NONBLOCK is not set in the
42 message queue description associated with mqdes, mq_send() shall block
43 until space becomes available to enqueue the message, or until
44 mq_send() is interrupted by a signal. If more than one thread is wait‐
45 ing to send when space becomes available in the message queue and the
46 Priority Scheduling option is supported, then the thread of the highest
47 priority that has been waiting the longest shall be unblocked to send
48 its message. Otherwise, it is unspecified which waiting thread is
49 unblocked. If the specified message queue is full and O_NONBLOCK is set
50 in the message queue description associated with mqdes, the message
51 shall not be queued and mq_send() shall return an error.
52 The mq_timedsend() function shall add a message to the message queue
54 specified by mqdes in the manner defined for the mq_send() function.
55 However, if the specified message queue is full and O_NONBLOCK is not
56 set in the message queue description associated with mqdes, the wait
57 for sufficient room in the queue shall be terminated when the specified
58 timeout expires. If O_NONBLOCK is set in the message queue description,
59 this function shall be equivalent to mq_send().
60 The timeout shall expire when the absolute time specified by abstime
62 passes, as measured by the clock on which timeouts are based (that is,
63 when the value of that clock equals or exceeds abstime), or if the
64 absolute time specified by abstime has already been passed at the time
65 of the call.
66 The timeout shall be based on the CLOCK_REALTIME clock. The resolution
68 of the timeout shall be the resolution of the clock on which it is
69 based. The timespec argument is defined in the <time.h> header.
70 Under no circumstance shall the operation fail with a timeout if there
72 is sufficient room in the queue to add the message immediately. The
73 validity of the abstime parameter need not be checked when there is
74 sufficient room in the queue.
75
77 Upon successful completion, the mq_send() and mq_timedsend() functions
78 shall return a value of zero. Otherwise, no message shall be enqueued,
79 the functions shall return -1, and errno shall be set to indicate the
80 error.
81
83 The mq_send() and mq_timedsend() functions shall fail if:
84 EAGAIN The O_NONBLOCK flag is set in the message queue description
86 associated with mqdes, and the specified message queue is full.
87 EBADF The mqdes argument is not a valid message queue descriptor open
89 for writing.
90 EINTR A signal interrupted the call to mq_send() or mq_timedsend().
92 EINVAL The value of msg_prio was outside the valid range.
94 EINVAL The process or thread would have blocked, and the abstime param‐
96 eter specified a nanoseconds field value less than zero or
97 greater than or equal to 1000 million.
98 EMSGSIZE
100 The specified message length, msg_len, exceeds the message size
101 attribute of the message queue.
102 ETIMEDOUT
104 The O_NONBLOCK flag was not set when the message queue was
105 opened, but the timeout expired before the message could be
106 added to the queue.
107 The following sections are informative.
109
111 None.
112
114 The value of the symbol {MQ_PRIO_MAX} limits the number of priority
115 levels supported by the application. Message priorities range from 0
116 to {MQ_PRIO_MAX}-1.
117
119 None.
120
122 None.
123
125 mq_open(), mq_receive(), mq_setattr(), time()
126 The Base Definitions volume of POSIX.1‐2017, <mqueue.h>, <time.h>
128
130 Portions of this text are reprinted and reproduced in electronic form
131 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
132 table Operating System Interface (POSIX), The Open Group Base Specifi‐
133 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
134 Electrical and Electronics Engineers, Inc and The Open Group. In the
135 event of any discrepancy between this version and the original IEEE and
136 The Open Group Standard, the original IEEE and The Open Group Standard
137 is the referee document. The original Standard can be obtained online
138 at http://www.opengroup.org/unix/online.html .
139 Any typographical or formatting errors that appear in this page are
141 most likely to have been introduced during the conversion of the source
142 files to man page format. To report such errors, see https://www.ker‐
143 nel.org/doc/man-pages/reporting_bugs.html .
144IEEE/The Open Group 2017 MQ_SEND(3P)