12-21-2008
Pointers reference process memory in the sending porocess. There is no guarantee that the pointer the receiver process gets will reference the same thing or anything at all.
Message queues work by passing data values not pointers to data.
Are you thinking about the msgtype value ( the first long in the msg struct). You can use this like a "pointer" - if you create message types 1...42 and use them only once, then you can get message id #13. But the processes have to agree ahead of time how many messages.
Last edited by jim mcnamara; 12-21-2008 at 06:02 AM..
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msgb(9S) Data Structures for Drivers msgb(9S)
NAME
msgb, mblk - STREAMS message block structure
SYNOPSIS
#include <sys/stream.h>
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI)
DESCRIPTION
A STREAMS message is made up of one or more message blocks, referenced by a pointer to a msgb structure. The b_next and b_prev pointers
are used to link messages together on a QUEUE. The b_cont pointer links message blocks together when a message consists of more than one
block.
Each msgb structure also includes a pointer to a datab(9S) structure, the data block (which contains pointers to the actual data of the
message), and the type of the message.
STRUCTURE MEMBERS
struct msgb *b_next; /* next message on queue */
struct msgb *b_prev; /* previous message on queue */
struct msgb *b_cont; /* next message block */
unsigned char *b_rptr; /* 1st unread data byte of buffer */
unsigned char *b_wptr; /* 1st unwritten data byte of buffer */
struct datab *b_datap; /* pointer to data block */
unsigned char b_band; /* message priority */
unsigned short b_flag; /* used by stream head */
Valid flags are as follows:
MSGMARK Last byte of message is marked.
MSGDELIM Message is delimited.
The msgb structure is defined as type mblk_t.
SEE ALSO
datab(9S)
Writing Device Drivers
STREAMS Programming Guide
SunOS 5.10 11 Apr 1991 msgb(9S)