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80a99f39 | 1 | '\" t |
c11b1abf | 2 | .\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> |
80a99f39 | 3 | .\" |
4b72fb64 | 4 | .\" %%%LICENSE_START(verbatim) |
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c13182ef | 13 | .\" |
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4b72fb64 | 24 | .\" %%%LICENSE_END |
80a99f39 | 25 | .\" |
50831f9b | 26 | .TH MQ_RECEIVE 3 2010-09-20 "Linux" "Linux Programmer's Manual" |
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27 | .SH NAME |
28 | mq_receive, mq_timedreceive \- receive a message from a message queue | |
29 | .SH SYNOPSIS | |
30 | .nf | |
31 | .B #include <mqueue.h> | |
32 | .sp | |
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33 | .BI "ssize_t mq_receive(mqd_t " mqdes ", char *" msg_ptr , |
34 | .BI " size_t " msg_len ", unsigned *" msg_prio ); | |
80a99f39 | 35 | .sp |
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36 | .B #include <time.h> |
37 | .B #include <mqueue.h> | |
38 | .sp | |
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39 | .BI "ssize_t mq_timedreceive(mqd_t " mqdes ", char *" msg_ptr , |
40 | .BI " size_t " msg_len ", unsigned *" msg_prio , | |
41 | .BI " const struct timespec *" abs_timeout ); | |
80a99f39 | 42 | .fi |
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43 | .sp |
44 | Link with \fI\-lrt\fP. | |
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45 | .sp |
46 | .ad l | |
47 | .in -4n | |
48 | Feature Test Macro Requirements for glibc (see | |
49 | .BR feature_test_macros (7)): | |
50 | .in | |
51 | .sp | |
52 | .BR mq_timedreceive (): | |
53 | .RS 4 | |
54 | _XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L | |
55 | .RE | |
56 | .ad | |
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57 | .SH DESCRIPTION |
58 | .BR mq_receive () | |
c13182ef MK |
59 | removes the oldest message with the highest priority from |
60 | the message queue referred to by the descriptor | |
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61 | .IR mqdes , |
62 | and places it in the buffer pointed to by | |
63 | .IR msg_ptr . | |
64 | The | |
65 | .I msg_len | |
66 | argument specifies the size of the buffer pointed to by | |
67 | .IR msg_ptr ; | |
68 | this must be greater than the | |
69 | .I mq_msgsize | |
c13182ef | 70 | attribute of the queue (see |
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71 | .BR mq_getattr (3)). |
72 | If | |
37f02e32 | 73 | .I msg_prio |
c13182ef | 74 | is not NULL, then the buffer to which it points is used |
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75 | to return the priority associated with the received message. |
76 | ||
77 | If the queue is empty, then, by default, | |
78 | .BR mq_receive () | |
79 | blocks until a message becomes available, | |
80 | or the call is interrupted by a signal handler. | |
c13182ef | 81 | If the |
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82 | .B O_NONBLOCK |
83 | flag is enabled for the message queue description, | |
84 | then the call instead fails immediately with the error | |
85 | .BR EAGAIN . | |
86 | ||
87 | .BR mq_timedreceive () | |
88 | behaves just like | |
89 | .BR mq_receive (), | |
90 | except that if the queue is empty and the | |
91 | .B O_NONBLOCK | |
92 | flag is not enabled for the message queue description, then | |
93 | .I abs_timeout | |
c13182ef | 94 | points to a structure which specifies a ceiling on the time for which |
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95 | the call will block. |
96 | This ceiling is an absolute timeout in seconds and nanoseconds | |
f49c451a | 97 | since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), and it is |
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98 | specified in the following structure: |
99 | .sp | |
bd191423 | 100 | .in +4n |
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101 | .nf |
102 | struct timespec { | |
103 | time_t tv_sec; /* seconds */ | |
104 | long tv_nsec; /* nanoseconds */ | |
105 | }; | |
106 | ||
107 | .fi | |
bd191423 | 108 | .in |
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109 | If no message is available, |
110 | and the timeout has already expired by the time of the call, | |
111 | .BR mq_timedreceive () | |
112 | returns immediately. | |
113 | .SH RETURN VALUE | |
114 | On success, | |
115 | .BR mq_receive () | |
116 | and | |
117 | .BR mq_timedreceive () | |
118 | return the number of bytes in the received message; | |
119 | on error, \-1 is returned, with | |
c13182ef | 120 | .I errno |
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121 | set to indicate the error. |
122 | .SH ERRORS | |
123 | .TP | |
124 | .B EAGAIN | |
125 | The queue was empty, and the | |
126 | .B O_NONBLOCK | |
127 | flag was set for the message queue description referred to by | |
128 | .IR mqdes . | |
129 | .TP | |
130 | .B EBADF | |
c13182ef | 131 | The descriptor specified in |
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132 | .I mqdes |
133 | was invalid. | |
134 | .TP | |
80a99f39 | 135 | .B EINTR |
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136 | The call was interrupted by a signal handler; see |
137 | .BR signal (7). | |
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138 | .TP |
139 | .B EINVAL | |
c13182ef | 140 | The call would have blocked, and |
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141 | .I abs_timeout |
142 | was invalid, either because | |
143 | .I tv_sec | |
144 | was less than zero, or because | |
c13182ef | 145 | .I tv_nsec |
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146 | was less than zero or greater than 1000 million. |
147 | .TP | |
eab64696 | 148 | .B EMSGSIZE |
0daa9e92 | 149 | .I msg_len |
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150 | was less than the |
151 | .I mq_msgsize | |
152 | attribute of the message queue. | |
153 | .TP | |
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154 | .B ETIMEDOUT |
155 | The call timed out before a message could be transferred. | |
156 | .SH CONFORMING TO | |
157 | POSIX.1-2001. | |
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158 | .SH NOTES |
159 | On Linux, | |
160 | .BR mq_timedreceive () | |
161 | is a system call, and | |
162 | .BR mq_receive () | |
163 | is a library function layered on top of that system call. | |
47297adb | 164 | .SH SEE ALSO |
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165 | .BR mq_close (3), |
166 | .BR mq_getattr (3), | |
167 | .BR mq_notify (3), | |
168 | .BR mq_open (3), | |
169 | .BR mq_send (3), | |
170 | .BR mq_unlink (3), | |
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171 | .BR mq_overview (7), |
172 | .BR time (7) |