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From: dce@smsc.sony.com (David Elliott)
Newsgroups: comp.sys.mac.programmer
Subject: Re: C function ptrs & Mac mem segments
Message-ID: <1990May2.144237.2978@smsc.sony.com>
Date: 2 May 90 14:42:37 GMT
References: <3550@dogie.macc.wisc.edu> <5524@helios.ee.lbl.gov>
Reply-To: dce@Sony.COM (David Elliott)
Organization: Sony Microsystems Corp.
Lines: 27

In article <5524@helios.ee.lbl.gov> beard@ux1.lbl.gov (Patrick C Beard) writes:
>Another point:  Even if the segment was unloaded, THINK C (and most other
>C compilers for the Mac that I've used) generates function pointers as
>pointers to jump table entries.  When you call a function by jump table,
>the segment is automatically loaded into memory (by the segment loader).

This is good news.

>As long as the jump table stays in memory, you don't have to worry about
>the staleness of the pointers in your structure.

How can this be assured?  For example, if one implements a new class
that has programmer-defined callbacks associated with it, how does one
save the callback function pointers so that these are assured to be
there?

I guess the real questions are:

	How do you make sure that the jump table stays in memory?

	What do you do if the jump table goes away?

-- 
David Elliott
dce@smsc.sony.com | ...!{uunet,mips}!sonyusa!dce
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