C++

[Peter Dufault]

On Friday, Jul 18, 2003, at 13:34 US/Eastern, Matthew Dillon wrote:

:As I understand it mp_SendMsg is a function pointer in the message 
port
:structure. It gets filled in when the port is created.
:

    Precisely.  mp_SendMsg() is controlled by the target port and thus 
is
    responsible for any frontend optimizations and conversions, 
including
    chaining.  mp_SendMsg is the 'agent' for the target port.

    This leads to all sorts of cool possibilities.  Inserting a shim
    becomes very easy, you would provide your own port that hides the
    real one and then you would do your own frontend processing.  For
    example:
    struct myport {
	MsgPort		port;
	MsgPort		*realport;
    }t;
    ...initialization of port...
    myport->port.mp_SendMsg = myfunc;
    myport->realport = originalport;
    And then:

    int
    myfunc(struct myport *port, Msg *msg)
    {
	if (message is something we want to play with) {
		...
	}
	/* else fall through to original port */
	return(port->realport->mp_SendMsg(port->realport, msg));
    }
    The port agent would be responsible for all sorts of things.  For
    example, in the kernel on a port representing entry into the TCP 
stack
    the port agent would be responsible for partitioning the work 
amoungst
    available TCP stack worker threads and forwarding the message

Did you consider using a subset of C++ for the kernel?  I'm asking 
because of this example and because I personally would have had to 
consider it because of the hand-built repetitive infrastructure of pure 
C.

I can see many drawbacks (enforcing a subset, issues associated with 
many fingers in the pie, etc) and I want to know what you thought about 
it.