Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!rutgers!cbmvax!mks
From: mks@cbmvax.commodore.com (Michael Sinz - CATS)
Newsgroups: comp.sys.amiga.tech
Subject: Re: CloseWindowSafely
Message-ID: <8976@cbmvax.commodore.com>
Date: 13 Dec 89 14:32:56 GMT
References: <5740@cps3xx.UUCP>
Reply-To: mks@cbmvax.commodore.com (Michael Sinz - CATS)
Organization: Commodore, West Chester, PA
Lines: 99

In article <5740@cps3xx.UUCP> porkka@frith.egr.msu.edu () writes:
>
>: From: ames!dtg.nsc.com!waggoner (Mark Waggoner)
>: To: porkka@frith.egr.msu.edu
>: Subject: CloseWindowSafely()
>: 
>: Hello,
>:   I've been following, and slightly involved in, the recent discussions
>: about sharing a message port among several windows.  I've used this method
>: before and, when closing a window, I merely made sure there were no messages
>: waiting at the msgport and did a normal CloseWindow().  I have seen
>This is basically exactly what CloseWindowSafely does.
>: you and others mention CloseWindowSafely a number of times but I can find no
>: mention of such a routine in the many manuals I have.  The closest they 
>: come to it is a strong warning to make sure you have no messages pending from
>: the window when it is closed.
>: 
>:   Can you give me the details of CloseWindowSafely() or send the code for it?
>: I want to be sure I am doing everything I can to prevent system crashes.
>: 
>: Thanks,
>:   Mark Waggoner
>:   waggoner@dtg.nsc.com
>: 
>
>Here is a rough sketch of CloseWindowSafely
>	CloseWindowSafely(win)
>	    struct Window *win;
>	{
>	    struct MsgPort myport = win->UserPort;
>	    struct Node *x, *y;
>	    struct IntuiMsg *t;
>
>	    SetIDCMP(win, 0L); /* Inhibit any further msgs for this window*/
>	    win->UserPort=0;   /* Prevent intuition from freeing my port */
>
>	    Forbid(); /* Prevent the Msg system from posting
>			 messages to "myport" while I fiddle with it */
>	    for(x=myport->head; x!=endoflist;x=y) {
>		y=x->next;
>		t=x;
>		if(t->window == win) Reply(x); /* Send it back*/
>	    }

You forgot to remove the message from the message port.  This could
cause (actually it WILL cause) a GURU.

Using the loop you have there, the line with the if(t->window...)
should be replaced by:

if(t->window==win)
{
   Remove(t);
   Reply(t);
}

>	    Permit();
>	    CloseWindow(win);
>	}
>
>Why all of this?
>Intuition keeps a list of all the msgs bodies that it has used
>for a particular window. When the window is closed, it simply FreeMems()
>them. If they are still part of a list (say, attached to a MsgPort)
>then that list will become currupted, and call Mr. GURU.
>
>So three thing need to be done before closing the window. First, stop
>intuition from sending any new msgs to the msgport from this window.
>Second clear the UserPort field of the Window so that intuition
>won't free the port for you, since you are still using it.
>Third, reply to msgs for this window that are already at the port,
>thusly removing them from the ports msg list.
>
>Then the window can be closed. The msgs that were used for this
>window will then be freed, which is OK since they are not part of
>you MsgPort msg list.
>
>For a working example see my "windows.c" code in my "hyperhelp" program.
>This example also deals with fonts. THis is archived at "uunet.uu.net"
>in the "pub/comp.sources.amiga" directory", or I could email it to
>you.
>
>The orignal "closeWindowSafely" is on a fishdisk I think.

And in an old AmigaMail and in the new RKM Libraries & Devices volume.

>
>It should also be in release 1.4 somewhere.
>
>I can't wait for 1.4.
> Joe Porkka   porkka@frith.egr.msu.edu

/----------------------------------------------------------------------\
|      /// Michael Sinz -- CATS/Amiga Software Engineer                |
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