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From: jesup@mizar.steinmetz (Randell Jesup)
Newsgroups: comp.sys.amiga
Subject: Re: Comments on the uniqueness of task & window id's
Message-ID: <6792@steinmetz.steinmetz.UUCP>
Date: Thu, 23-Jul-87 17:07:17 EDT
Article-I.D.: steinmet.6792
Posted: Thu Jul 23 17:07:17 1987
Date-Received: Sat, 25-Jul-87 08:35:51 EDT
References: <8706260543.AA20346@cogsci.berkeley.edu> <4445@ihlpa.ATT.COM> <6752@steinmetz.steinmetz.UUCP> <198@dana.UUCP>
Sender: root@steinmetz.steinmetz.UUCP
Reply-To: jesup@sungod.steinmetz.UUCP (Randell Jesup)
Organization: General Electric CRD, Schenectady, NY
Lines: 73
Keywords: ID-handler

In article <198@dana.UUCP> rap@dana.UUCP (Rob Peck) writes:
>I encountered a problem that couldnt be solved with Forbid(), Permit() and
>FindPort().  In particular, I created a master program, that called
>test().  test() is something that runs a graphics demo of some kind;
>it creates a window of a fixed size, and puts it on a custom screen
>whose address it locates by issuing FindPort(myscreen).  An addendum
>to the port structure itself is the address of the custom screen.
>
>The master program NOW does:
>
>	Disable();
>	port = FindPort(myscreen);
>	if(port == 0)
>		/* .... create the port if not there ... */
>		/* open a custom screen, put the address of
>		 * custom screen into addendum to the port;
>		 * set users_of_screen = 1
>		 */
>	Enable();
>	test();
>	...    	 users_of_screen = users_of_screen -1;
>
>		 (another addendum to the custom port)
>
>	if(users_of_screen = 0) CloseScreen(myscreen);
...
>Rob Peck.	...ihnp4!hplabs!dana!rap

	How about this:  (By the way, how is your port associated with
			  you Screen???)
main()
{
	...
	Forbid();
	if (port = FindPort(myportname))
	{
		<somehow find the Screen from the port>
		<update user count by 1>
	} else {
		<create port, set user count to 1>
		<Open screen, put in port>
		/* you might not want to forbid that long, so you might
		   want to set users to 0 until the screen opened, and
		   have somewthing that finds the port busy wait on the
		   Screen variable.  A bit bizarre, and I think it's ok
		   to open a screen inside a Forbid(). */
	}
	Permit();

	Test();
	...

	Forbid();
	if (<user count> = 1)
	{
		CloseScreen(<screen>);
		RemPort(myportname);
	} else
		<user count>--;
	Permit();
	...
}

	Actually, if I wanted to bother learning how they work I'm sure that
semaphores would make this easier.  Most problems I've dealt with using
Forbid and Permit were coming up with unique ports, for example for a shell
that has a port for receiving messages from sub-processes.  I just Forbid,
and then look for Shell_port_1.  If it's there, I look for shell_port_2, etc.
When I've found an unused port, I create it, then Permit.

	Randell Jesup
	jesup@ge-crd.arpa
	jesup@steinmetz.uucp (uunet!steinmetz!jesup)