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>
24 #include <time.h>
25 int mq_timedsend(mqd_t mqdes, const char *msg_ptr, size_t msg_len,
26 unsigned msg_prio, const struct timespec *abs_timeout);
27
30 The mq_send() function shall add the message pointed to by the argument
31 msg_ptr to the message queue specified by mqdes. The msg_len argument
32 specifies the length of the message, in bytes, pointed to by msg_ptr.
33 The value of msg_len shall be less than or equal to the mq_msgsize
34 attribute of the message queue, or mq_send() shall fail.
35 If the specified message queue is not full, mq_send() shall behave as
37 if the message is inserted into the message queue at the position indi‐
38 cated by the msg_prio argument. A message with a larger numeric value
39 of msg_prio shall be inserted before messages with lower values of
40 msg_prio. A message shall be inserted after other messages in the
41 queue, if any, with equal msg_prio. The value of msg_prio shall be less
42 than {MQ_PRIO_MAX}.
43 If the specified message queue is full and O_NONBLOCK is not set in the
45 message queue description associated with mqdes, mq_send() shall block
46 until space becomes available to enqueue the message, or until
47 mq_send() is interrupted by a signal. If more than one thread is wait‐
48 ing to send when space becomes available in the message queue and the
49 Priority Scheduling option is supported, then the thread of the highest
50 priority that has been waiting the longest shall be unblocked to send
51 its message. Otherwise, it is unspecified which waiting thread is
52 unblocked. If the specified message queue is full and O_NONBLOCK is
53 set in the message queue description associated with mqdes, the message
54 shall not be queued and mq_send() shall return an error.
55 The mq_timedsend() function shall add a message to the message queue
57 specified by mqdes in the manner defined for the mq_send() function.
58 However, if the specified message queue is full and O_NONBLOCK is not
59 set in the message queue description associated with mqdes, the wait
60 for sufficient room in the queue shall be terminated when the specified
61 timeout expires. If O_NONBLOCK is set in the message queue description,
62 this function shall be equivalent to mq_send().
63 The timeout shall expire when the absolute time specified by abs_time‐
65 out passes, as measured by the clock on which timeouts are based (that
66 is, when the value of that clock equals or exceeds abs_timeout), or if
67 the absolute time specified by abs_timeout has already been passed at
68 the time of the call.
69 If the Timers option is supported, the timeout shall be based on the
71 CLOCK_REALTIME clock; if the Timers option is not supported, the time‐
72 out shall be based on the system clock as returned by the time() func‐
73 tion.
74 The resolution of the timeout shall be the resolution of the clock on
76 which it is based. The timespec argument is defined in the <time.h>
77 header.
78 Under no circumstance shall the operation fail with a timeout if there
80 is sufficient room in the queue to add the message immediately. The
81 validity of the abs_timeout parameter need not be checked when there is
82 sufficient room in the queue.
83
85 Upon successful completion, the mq_send() and mq_timedsend() functions
86 shall return a value of zero. Otherwise, no message shall be enqueued,
87 the functions shall return -1, and errno shall be set to indicate the
88 error.
89
91 The mq_send() and mq_timedsend() functions shall fail if:
92 EAGAIN The O_NONBLOCK flag is set in the message queue description
94 associated with mqdes, and the specified message queue is full.
95 EBADF The mqdes argument is not a valid message queue descriptor open
97 for writing.
98 EINTR A signal interrupted the call to mq_send() or mq_timedsend().
100 EINVAL The value of msg_prio was outside the valid range.
102 EINVAL The process or thread would have blocked, and the abs_timeout
104 parameter specified a nanoseconds field value less than zero or
105 greater than or equal to 1000 million.
106 EMSGSIZE
108 The specified message length, msg_len, exceeds the message size
109 attribute of the message queue.
110 ETIMEDOUT
112 The O_NONBLOCK flag was not set when the message queue was
113 opened, but the timeout expired before the message could be
114 added to the queue.
115 The following sections are informative.
118
120 None.
121
123 The value of the symbol {MQ_PRIO_MAX} limits the number of priority
124 levels supported by the application. Message priorities range from 0 to
125 {MQ_PRIO_MAX}-1.
126
128 None.
129
131 None.
132
134 mq_open(), mq_receive(), mq_setattr(), mq_timedreceive(), time(), the
135 Base Definitions volume of IEEE Std 1003.1-2001, <mqueue.h>, <time.h>
136
138 Portions of this text are reprinted and reproduced in electronic form
139 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
140 -- Portable Operating System Interface (POSIX), The Open Group Base
141 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
142 Electrical and Electronics Engineers, Inc and The Open Group. In the
143 event of any discrepancy between this version and the original IEEE and
144 The Open Group Standard, the original IEEE and The Open Group Standard
145 is the referee document. The original Standard can be obtained online
146 at http://www.opengroup.org/unix/online.html .
147IEEE/The Open Group 2003 MQ_SEND(3P)