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26 .TH MQ_SEND 3 2017-09-15 "Linux" "Linux Programmer's Manual"
28 mq_send, mq_timedsend \- send a message to a message queue
31 .B #include <mqueue.h>
33 .BI "int mq_send(mqd_t " mqdes ", const char *" msg_ptr ,
34 .BI " size_t " msg_len ", unsigned int " msg_prio );
37 .B #include <mqueue.h>
39 .BI "int mq_timedsend(mqd_t " mqdes ", const char *" msg_ptr ,
40 .BI " size_t " msg_len ", unsigned int " msg_prio ,
41 .BI " const struct timespec *" abs_timeout );
44 Link with \fI\-lrt\fP.
48 Feature Test Macro Requirements for glibc (see
49 .BR feature_test_macros (7)):
54 _POSIX_C_SOURCE\ >=\ 200112L
59 adds the message pointed to by
61 to the message queue referred to by the message queue descriptor
65 argument specifies the length of the message pointed to by
67 this length must be less than or equal to the queue's
70 Zero-length messages are allowed.
74 argument is a nonnegative integer that specifies the priority
76 Messages are placed on the queue in decreasing order of priority,
77 with newer messages of the same priority being placed after
78 older messages with the same priority.
81 for details on the range for the message priority.
83 If the message queue is already full
84 (i.e., the number of messages on the queue equals the queue's
86 attribute), then, by default,
88 blocks until sufficient space becomes available to allow the message
89 to be queued, or until the call is interrupted by a signal handler.
92 flag is enabled for the message queue description,
93 then the call instead fails immediately with the error
99 except that if the queue is full and the
101 flag is not enabled for the message queue description, then
103 points to a structure which specifies how long the call will block.
104 This value is an absolute timeout in seconds and nanoseconds
105 since the Epoch, 1970-01-01 00:00:00 +0000 (UTC),
106 specified in the following structure:
111 time_t tv_sec; /* seconds */
112 long tv_nsec; /* nanoseconds */
117 If the message queue is full,
118 and the timeout has already expired by the time of the call,
126 return zero; on error, \-1 is returned, with
128 set to indicate the error.
132 The queue was full, and the
134 flag was set for the message queue description referred to by
138 The descriptor specified in
140 was invalid or not opened for writing.
143 The call was interrupted by a signal handler; see
147 The call would have blocked, and
149 was invalid, either because
151 was less than zero, or because
153 was less than zero or greater than 1000 million.
159 attribute of the message queue.
162 The call timed out before a message could be transferred.
164 For an explanation of the terms used in this section, see
170 Interface Attribute Value
174 T} Thread safety MT-Safe
177 POSIX.1-2001, POSIX.1-2008.
181 is a system call, and
183 is a library function layered on top of that system call.