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1 | '\" t |
2 | .\" Hey Emacs! This file is -*- nroff -*- source. | |
3 | .\" | |
c11b1abf | 4 | .\" Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com> |
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c13182ef | 14 | .\" |
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c13182ef | 22 | .\" |
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23 | .\" Formatted or processed versions of this manual, if unaccompanied by |
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25 | .\" | |
d9343c5c | 26 | .TH MQ_RECEIVE 3 2006-02-25 "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 ); | |
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35 | .sp |
36 | .B #define _XOPEN_SOURCE 600 | |
37 | .B #include <time.h> | |
38 | .B #include <mqueue.h> | |
39 | .sp | |
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40 | .BI "ssize_t mq_timedreceive(mqd_t " mqdes ", char *" msg_ptr , |
41 | .BI " size_t " msg_len ", unsigned *" msg_prio , | |
42 | .BI " const struct timespec *" abs_timeout ); | |
80a99f39 | 43 | .fi |
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44 | .sp |
45 | Link with \fI\-lrt\fP. | |
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46 | .SH DESCRIPTION |
47 | .BR mq_receive () | |
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48 | removes the oldest message with the highest priority from |
49 | the message queue referred to by the descriptor | |
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50 | .IR mqdes , |
51 | and places it in the buffer pointed to by | |
52 | .IR msg_ptr . | |
53 | The | |
54 | .I msg_len | |
55 | argument specifies the size of the buffer pointed to by | |
56 | .IR msg_ptr ; | |
57 | this must be greater than the | |
58 | .I mq_msgsize | |
c13182ef | 59 | attribute of the queue (see |
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60 | .BR mq_getattr (3)). |
61 | If | |
62 | .I prio | |
c13182ef | 63 | is not NULL, then the buffer to which it points is used |
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64 | to return the priority associated with the received message. |
65 | ||
66 | If the queue is empty, then, by default, | |
67 | .BR mq_receive () | |
68 | blocks until a message becomes available, | |
69 | or the call is interrupted by a signal handler. | |
c13182ef | 70 | If the |
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71 | .B O_NONBLOCK |
72 | flag is enabled for the message queue description, | |
73 | then the call instead fails immediately with the error | |
74 | .BR EAGAIN . | |
75 | ||
76 | .BR mq_timedreceive () | |
77 | behaves just like | |
78 | .BR mq_receive (), | |
79 | except that if the queue is empty and the | |
80 | .B O_NONBLOCK | |
81 | flag is not enabled for the message queue description, then | |
82 | .I abs_timeout | |
c13182ef | 83 | points to a structure which specifies a ceiling on the time for which |
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84 | the call will block. |
85 | This ceiling is an absolute timeout in seconds and nanoseconds | |
86 | since the Epoch (midnight on the morning of 1 January 1970), | |
87 | specified in the following structure: | |
88 | .sp | |
bd191423 | 89 | .in +4n |
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90 | .nf |
91 | struct timespec { | |
92 | time_t tv_sec; /* seconds */ | |
93 | long tv_nsec; /* nanoseconds */ | |
94 | }; | |
95 | ||
96 | .fi | |
bd191423 | 97 | .in |
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98 | If no message is available, |
99 | and the timeout has already expired by the time of the call, | |
100 | .BR mq_timedreceive () | |
101 | returns immediately. | |
102 | .SH RETURN VALUE | |
103 | On success, | |
104 | .BR mq_receive () | |
105 | and | |
106 | .BR mq_timedreceive () | |
107 | return the number of bytes in the received message; | |
108 | on error, \-1 is returned, with | |
c13182ef | 109 | .I errno |
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110 | set to indicate the error. |
111 | .SH ERRORS | |
112 | .TP | |
113 | .B EAGAIN | |
114 | The queue was empty, and the | |
115 | .B O_NONBLOCK | |
116 | flag was set for the message queue description referred to by | |
117 | .IR mqdes . | |
118 | .TP | |
119 | .B EBADF | |
c13182ef | 120 | The descriptor specified in |
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121 | .I mqdes |
122 | was invalid. | |
123 | .TP | |
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124 | .B EINTR |
125 | The call was interrupted by a signal handler. | |
126 | .TP | |
127 | .B EINVAL | |
c13182ef | 128 | The call would have blocked, and |
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129 | .I abs_timeout |
130 | was invalid, either because | |
131 | .I tv_sec | |
132 | was less than zero, or because | |
c13182ef | 133 | .I tv_nsec |
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134 | was less than zero or greater than 1000 million. |
135 | .TP | |
eab64696 | 136 | .B EMSGSIZE |
0daa9e92 | 137 | .I msg_len |
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138 | was less than the |
139 | .I mq_msgsize | |
140 | attribute of the message queue. | |
141 | .TP | |
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142 | .B ETIMEDOUT |
143 | The call timed out before a message could be transferred. | |
144 | .SH CONFORMING TO | |
145 | POSIX.1-2001. | |
146 | .SH "SEE ALSO" | |
147 | .BR mq_close (3), | |
148 | .BR mq_getattr (3), | |
149 | .BR mq_notify (3), | |
150 | .BR mq_open (3), | |
151 | .BR mq_send (3), | |
152 | .BR mq_unlink (3), | |
0a90178c | 153 | .BR feature_test_macros (7), |
80a99f39 | 154 | .BR mq_overview (7) |