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From: shs@ji.Berkeley.EDU.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Intuition's "dont mess with these" fields...
Message-ID: <21519@ucbvax.BERKELEY.EDU>
Date: Fri, 30-Oct-87 01:21:11 EST
Article-I.D.: ucbvax.21519
Posted: Fri Oct 30 01:21:11 1987
Date-Received: Sun, 1-Nov-87 06:22:36 EST
References: <1961@amiga.amiga.UUCP> <1825@cadovax.UUCP> <21469@ucbvax.BERKELEY.EDU> <1830@cadovax.UUCP>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: shs@ji.Berkeley.EDU.UUCP (Steve Schoettler)
Organization: University of California, Berkeley
Lines: 41
Keywords: Intuition lockibase forbid
Summary: PLEASE dont FORBID!

In article <1830@cadovax.UUCP> keithd@cadovax.UUCP (Keith Doyle) writes:
>>	key=LockIBase(0L);
>>	/* Do funny stuff here... but not much of it... be QUICK! */
>>	UnlockIBase(key);
>
>Sounds reasonable.  Is this any better/worse/different than doing a
>Forbid()/Permit() or an Enable()/Disable() ?

  YES!!!

  The main difference is that LockIBase allows other tasks to run
(except ones that want to LockIBase also).

  Forbid() prevents other tasks from running.  This may be necessary
for some programs, but should be used as little as possible.  In all
cases if LockIBase() is sufficient, use it over Forbid (it should be
sufficient for any Intuition meddling).

  Disable() is the worst of the three and prevents other interrupts
from occurring.  This means trackdisk, video, timers, etc.
For passing data (semaphores) between user processes, Forbid() is
sufficient, unless you think some interrupt handler is going to mess
with your data.

  *** 

  I cannot stress enough a frugal use of Forbid()/Permit().  Many 
programmers don't think too hard about this and just stick it in
for safety.
  If you are running a multiple processor configuration, this means
that all processors must stop.  I'm not kidding here.  Think about
tasks on a stock Amiga that you will be halting.  Then think ahead
some more.  In the not too far future, there will be multiple
processors running in Amiga cards, and the only way to deal with
a Forbid() on one is to stop them all.  Although necessary for some
applications, this is very painful.

  Please be a good citizen and limit Forbid and Disable as much
as possible.

Steve Schoettler