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26 .TH MQ_RECEIVE 3 2017-09-15 "Linux" "Linux Programmer's Manual"
28 mq_receive, mq_timedreceive \- receive a message from a message queue
31 .B #include <mqueue.h>
33 .BI "ssize_t mq_receive(mqd_t " mqdes ", char *" msg_ptr ,
34 .BI " size_t " msg_len ", unsigned int *" msg_prio );
37 .B #include <mqueue.h>
39 .BI "ssize_t mq_timedreceive(mqd_t " mqdes ", 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)):
52 .BR mq_timedreceive ():
54 _POSIX_C_SOURCE\ >=\ 200112L
59 removes the oldest message with the highest priority from
60 the message queue referred to by the message queue descriptor
62 and places it in the buffer pointed to by
66 argument specifies the size of the buffer pointed to by
68 this must be greater than or equal to the
70 attribute of the queue (see
74 is not NULL, then the buffer to which it points is used
75 to return the priority associated with the received message.
77 If the queue is empty, then, by default,
79 blocks until a message becomes available,
80 or the call is interrupted by a signal handler.
83 flag is enabled for the message queue description,
84 then the call instead fails immediately with the error
87 .BR mq_timedreceive ()
90 except that if the queue is empty and the
92 flag is not enabled for the message queue description, then
94 points to a structure which specifies how long the call will block.
95 This value is an absolute timeout in seconds and nanoseconds
96 since the Epoch, 1970-01-01 00:00:00 +0000 (UTC),
97 specified in the following structure:
102 time_t tv_sec; /* seconds */
103 long tv_nsec; /* nanoseconds */
108 If no message is available,
109 and the timeout has already expired by the time of the call,
110 .BR mq_timedreceive ()
116 .BR mq_timedreceive ()
117 return the number of bytes in the received message;
118 on error, \-1 is returned, with
120 set to indicate the error.
124 The queue was empty, and the
126 flag was set for the message queue description referred to by
130 The descriptor specified in
132 was invalid or not opened for reading.
135 The call was interrupted by a signal handler; see
139 The call would have blocked, and
141 was invalid, either because
143 was less than zero, or because
145 was less than zero or greater than 1000 million.
151 attribute of the message queue.
154 The call timed out before a message could be transferred.
156 For an explanation of the terms used in this section, see
162 Interface Attribute Value
165 .BR mq_timedreceive ()
166 T} Thread safety MT-Safe
169 POSIX.1-2001, POSIX.1-2008.
172 .BR mq_timedreceive ()
173 is a system call, and
175 is a library function layered on top of that system call.