Path: utzoo!mnetor!uunet!husc6!mailrus!nrl-cmf!ames!oliveb!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: IPC - A proposal
Message-ID: <44626@sun.uucp>
Date: 8 Mar 88 17:51:22 GMT
References: <5375@well.UUCP> <739@nuchat.UUCP> <7455@agate.BERKELEY.EDU> <2116@polya.STANFORD.EDU>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 42

In article <2116@polya.STANFORD.EDU> (Tomas G. Rokicki) writes:
>                                                 ...  Do the above,
> and everything's hunky-dory, except you have a FindPort() within
> Forbid()/Permit() . . .

Hmmm, the problem everyone is complaining about is the speed of doing
a FindPort() which takes to long. Maybe what we need instead is a 
way of checking to see that a port we originally got was still valid
and then encased the destruction of the port and sending to the port
in F/P pairs. As an illustration :

In the client :
	/* in the init section */
	port = FindPort("Foobar.port");
	/* in the loop */
	Forbid();
	If (IsValidPort(port)) PutMsg(port,msg);
	Permit();

In the server :
	/* in the init section */
	port = CreatePort("Foobar.port");

	/* in the exit code */
	Forbid();
	MoveMsgList(port,safearea);
	NewDeletePort(port); /* Marks memory pointed to by port as invalid */
	Permit();
	ReplyAllMsgs(safearea);
	exit(0);

Note that the NewDeletePort() would scribble on the port in some way to make
it appear invalid (nulling out the memory would be sufficient) The the client
task knows that port is now invalid and won't send to it. Then the server
sends replies to all the messages that were queued. And exits. If all of the
clients follow this rule then A) it is fast (IsValidPort could be as simple
as port.mn_Type == NT_MESSAGE) and B) it is reasonably safe from race 
conditions.

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.