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System Calls msgrcv(2)
NAME
msgrcv - message receive operation
SYNOPSIS
#include <sys/msg.h>
ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long int
msgtyp, int msgflg);
DESCRIPTION
The msgrcv() function reads a message from the queue associ-
ated with the message queue identifier specified by msqid
and places it in the user-defined buffer pointed to by msgp.
The msgp argument points to a user-defined buffer that must
contain first a field of type long int that will specify the
type of the message, and then a data portion that will hold
the data bytes of the message. The structure below is an
example of what this user-defined buffer might look like:
struct mymsg {
long int mtype; /* message type */
char mtext[1]; /* message text */
}
The mtype member is the received message's type as specified
by the sending process.
The mtext member is the text of the message.
The msgsz argument specifies the size in bytes of mtext.
The received message is truncated to msgsz bytes if it is
larger than msgsz and (msgflg&MSG_NOERROR) is non-zero. The
truncated part of the message is lost and no indication of
the truncation is given to the calling process.
The msgtyp argument specifies the type of message requested
as follows:
o If msgtyp is 0, the first message on the queue is
received.
o If msgtyp is greater than 0, the first message of type
msgtyp is received.
o If msgtyp is less than 0, the first message of the
lowest type that is less than or equal to the absolute
value of msgtyp is received.
SunOS 5.10 Last change: 19 May 1999 1
System Calls msgrcv(2)
The msgflg argument specifies which of the following actions
is to be taken if a message of the desired type is not on
the queue:
o If (msgflg&IPC_NOWAIT) is non-zero, the calling process
will return immediately with a return value of -1 and
errno set to ENOMSG.
o If (msgflg&IPC_NOWAIT) is 0, the calling process will
suspend execution until one of the following occurs:
o A message of the desired type is placed on the
queue.
o The message queue identifier msqid is removed from
the system (see msgctl(2)); when this occurs,
errno is set equal to EIDRM and -1 is returned.
o The calling process receives a signal that is to
be caught; in this case a message is not received
and the calling process resumes execution in the
manner prescribed in sigaction(2).
Upon successful completion, the following actions are taken
with respect to the data structure associated with msqid
(see intro(2)):
o msg_qnum is decremented by 1.
o msg_lrpid is set equal to the process ID of the calling
process.
o msg_rtime is set equal to the current time.
RETURN VALUES
Upon successful completion, msgrcv() returns a value equal
to the number of bytes actually placed into the buffer
mtext. Otherwise, -1 is returned, no message is received,
and errno is set to indicate the error.
ERRORS
The msgrcv() function will fail if:
E2BIG The value of mtext is greater than msgsz and
(msgflg&MSG_NOERROR) is 0.
SunOS 5.10 Last change: 19 May 1999 2
System Calls msgrcv(2)
EACCES Operation permission is denied to the cal-
ling process. See intro(2).
EIDRM The message queue identifier msqid is
removed from the system.
EINTR The msgrcv() function was interrupted by a
signal.
EINVAL The msqid argument is not a valid message
queue identifier.
ENOMSG The queue does not contain a message of the
desired type and (msgflg&IPC_NOWAIT) is
non-zero.
The msgrcv() function may fail if:
EFAULT The msgp argument points to an illegal
address.
USAGE
The value passed as the msgp argument should be converted to
type void *.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
SEE ALSO
intro(2), msgctl(2), msgget(2), msgsnd(2), sigaction(2),
attributes(5), standards(5)
SunOS 5.10 Last change: 19 May 1999 3
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This page was generated on Wed Sep 12 11:27:03 GMT 2007
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