1 .\" $NetBSD: msgrcv.2,v 1.1 1995/10/16 23:49:20 jtc Exp $
3 .\" Copyright (c) 1995 Frank van der Linden
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16 .\" This product includes software developed for the NetBSD Project
17 .\" by Frank van der Linden
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32 .\" $FreeBSD: src/lib/libc/gen/msgrcv.3,v 1.8.2.7 2003/03/15 15:11:05 trhodes Exp $
39 .Nd receive a message from a message queue
47 .Fn msgrcv "int msqid" "void *msgp" "size_t msgsz" "long msgtyp" "int msgflg"
51 system call receives a message from the message queue specified in
53 and places it into the structure pointed to by
55 This structure should consist of the following members:
57 long mtype; /* message type */
58 char mtext[1]; /* body of message */
62 is an integer greater than 0 that can be used for selecting messages,
64 is an array of bytes, with a size up to that of the system limit
69 has one of the following meanings:
75 is greater than 0. The first message of type
82 is equal to 0. The first message on the queue will be received.
87 is less than 0. The first message of the lowest message type that is
88 less than or equal to the absolute value of
96 specifies the maximum length of the requested message.
98 message has a length greater than
100 it will be silently truncated if the
104 otherwise an error will be returned.
106 If no matching message is present on the message queue specified by
110 depends on whether the
119 will immediately return a value of -1, and set
125 is not set, the calling process will be blocked
129 A message of the requested type becomes available on the message queue.
131 The message queue is removed, in which case -1 will be returned, and
136 A signal is received and caught. -1 is returned, and
142 If a message is successfully received, the data structure associated with
144 is updated as follows:
148 is decremented by the size of the message.
151 is set to the pid of the caller.
154 is set to the current time.
160 Upon successful completion,
162 returns the number of bytes received into the
164 field of the structure pointed to by
166 Otherwise, -1 is returned, and
168 set to indicate the error.
170 The XSI Interprocess Communication family of functions is also available
171 as an implementation in userspace.
174 daemon has to be running.
178 variable is set in a process' environment, the process and its children
179 will use the userspace implementation.
183 system call will fail if:
189 is not a valid message queue identifier.
191 The message queue was removed while
193 was waiting for a message of the requested type to become available on it.
200 A matching message was received, but its size was greater than
207 The calling process does not have read access to the message queue.
212 points to an invalid address.
214 The system call was interrupted by the delivery of a signal.
216 There is no message of the requested type available on the message queue,
227 Message queues appeared in the first release of
233 specific userspace implementation (see
244 error value, which should be used in
245 the case of a removed message queue, nor the
248 should be used when no suitable message is available and