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
13 mq_send, mq_timedsend — send a message to a message queue (REALTIME)
14
16 #include <mqueue.h>
17 int mq_send(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
19 unsigned msg_prio);
20 #include <mqueue.h>
22 #include <time.h>
23 int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
25 unsigned msg_prio, const struct timespec *abstime);
26
28 The mq_send() function shall add the message pointed to by the argument
29 msg_ptr to the message queue specified by mqdes. The msg_len argument
30 specifies the length of the message, in bytes, pointed to by msg_ptr.
31 The value of msg_len shall be less than or equal to the mq_msgsize
32 attribute of the message queue, or mq_send() shall fail.
33 If the specified message queue is not full, mq_send() shall behave as
35 if the message is inserted into the message queue at the position indi‐
36 cated by the msg_prio argument. A message with a larger numeric value
37 of msg_prio shall be inserted before messages with lower values of
38 msg_prio. A message shall be inserted after other messages in the
39 queue, if any, with equal msg_prio. The value of msg_prio shall be
40 less than {MQ_PRIO_MAX}.
41 If the specified message queue is full and O_NONBLOCK is not set in the
43 message queue description associated with mqdes, mq_send() shall block
44 until space becomes available to enqueue the message, or until
45 mq_send() is interrupted by a signal. If more than one thread is wait‐
46 ing to send when space becomes available in the message queue and the
47 Priority Scheduling option is supported, then the thread of the highest
48 priority that has been waiting the longest shall be unblocked to send
49 its message. Otherwise, it is unspecified which waiting thread is
50 unblocked. If the specified message queue is full and O_NONBLOCK is set
51 in the message queue description associated with mqdes, the message
52 shall not be queued and mq_send() shall return an error.
53 The mq_timedsend() function shall add a message to the message queue
55 specified by mqdes in the manner defined for the mq_send() function.
56 However, if the specified message queue is full and O_NONBLOCK is not
57 set in the message queue description associated with mqdes, the wait
58 for sufficient room in the queue shall be terminated when the specified
59 timeout expires. If O_NONBLOCK is set in the message queue description,
60 this function shall be equivalent to mq_send().
61 The timeout shall expire when the absolute time specified by abstime
63 passes, as measured by the clock on which timeouts are based (that is,
64 when the value of that clock equals or exceeds abstime), or if the
65 absolute time specified by abstime has already been passed at the time
66 of the call.
67 The timeout shall be based on the CLOCK_REALTIME clock. The resolution
69 of the timeout shall be the resolution of the clock on which it is
70 based. The timespec argument is defined in the <time.h> header.
71 Under no circumstance shall the operation fail with a timeout if there
73 is sufficient room in the queue to add the message immediately. The
74 validity of the abstime parameter need not be checked when there is
75 sufficient room in the queue.
76
78 Upon successful completion, the mq_send() and mq_timedsend() functions
79 shall return a value of zero. Otherwise, no message shall be enqueued,
80 the functions shall return −1, and errno shall be set to indicate the
81 error.
82
84 The mq_send() and mq_timedsend() functions shall fail if:
85 EAGAIN The O_NONBLOCK flag is set in the message queue description
87 associated with mqdes, and the specified message queue is full.
88 EBADF The mqdes argument is not a valid message queue descriptor open
90 for writing.
91 EINTR A signal interrupted the call to mq_send() or mq_timedsend().
93 EINVAL The value of msg_prio was outside the valid range.
95 EINVAL The process or thread would have blocked, and the abstime param‐
97 eter specified a nanoseconds field value less than zero or
98 greater than or equal to 1000 million.
99 EMSGSIZE
101 The specified message length, msg_len, exceeds the message size
102 attribute of the message queue.
103 ETIMEDOUT
105 The O_NONBLOCK flag was not set when the message queue was
106 opened, but the timeout expired before the message could be
107 added to the queue.
108 The following sections are informative.
110
112 None.
113
115 The value of the symbol {MQ_PRIO_MAX} limits the number of priority
116 levels supported by the application. Message priorities range from 0
117 to {MQ_PRIO_MAX}−1.
118
120 None.
121
123 None.
124
126 mq_open(), mq_receive(), mq_setattr(), time()
127 The Base Definitions volume of POSIX.1‐2008, <mqueue.h>, <time.h>
129
131 Portions of this text are reprinted and reproduced in electronic form
132 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
133 -- Portable Operating System Interface (POSIX), The Open Group Base
134 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
135 cal and Electronics Engineers, Inc and The Open Group. (This is
136 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
137 event of any discrepancy between this version and the original IEEE and
138 The Open Group Standard, the original IEEE and The Open Group Standard
139 is the referee document. The original Standard can be obtained online
140 at http://www.unix.org/online.html .
141 Any typographical or formatting errors that appear in this page are
143 most likely to have been introduced during the conversion of the source
144 files to man page format. To report such errors, see https://www.ker‐
145 nel.org/doc/man-pages/reporting_bugs.html .
146IEEE/The Open Group 2013 MQ_SEND(3P)