Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!oliveb!apple!han
From: han@Apple.COM (Byron Han, wyl E. coyote )
Newsgroups: comp.sys.mac.programmer
Subject: Re: Calling Code resources?
Message-ID: <28579@apple.Apple.COM>
Date: 7 Apr 89 19:56:18 GMT
References: <11817@ut-emx.UUCP> <28576@apple.Apple.COM>
Distribution: usa
Organization: Apple R&D - Networking & Communications
Lines: 55

In article <28576@apple.Apple.COM> austing@Apple.COM (Glenn L. Austin) writes:
>In article <11817@ut-emx.UUCP> newman@ut-emx.UUCP (David Newman) writes:
>>Here is another question for the net-gods:  how do you call a
>>code resource (like an XCMD or whatever) from another piece of
>>code?  Can it be done from a high-level language?  How might it
>>be done in Pascal?
>
>In C, it is really *relatively* simple -- all you need to do is create a
>function pointer.  In Pascal, however, you need to have an assembly-language
>routine to do the actual call.  Basically, in order to call a code resource,
>you need to do the following steps:
>
>1) Load the resource into the heap (with your favorite GetResource call)
>2) Move the resource high into the heap (with MoveHHi)
>3) Lock the resource (with HLock)
>4) Dereference the Handle (C: *handle, Pascal: handle^)
>5) Assign the dereferenced handle to your function pointer in C.  In Pascal,
>   it depends upon the implementation of your assembly language routine.
>6) Call the function!
>
To wit, if you have a code resource with entry point 
     FUNCTION foom(a, b, c, d, e, f):g
you create a pascal function of the following
    FUNCTION  callfoom(a, b, c, d, e, f, x:LONGINT):g; INLINE $205F,$4E90

To call the code resource, use callfoom instead and pass the dereferenced
handle as the final argument. 

Doing it from assembler makes more sense to me since you have better
control over register saving and assembler is more efficient.  By the
way if you are doing this from assembler, it is a REALLY GOOD IDEA to
save registers...

2. Memory management.  If the code resource has the locked bit set, the
code resource will be loaded as low as possible in memory (via ResrvMem)
so moving it high has no effect.  If the code resource is not locked, and 
you don't plan to use the code resource for a "long" time, you
should explicitly lock it and call MoveHHi prior to that.  And HUnlock it
when done.

If you plan to use the resource for a long period of time and are not
sure if the resource has the locked bit set, you should explictly call
ResrvMem to get it as low as possible in the heap.

+-----------------------------------------------------------------------------+
| Disclaimer: Apple has no connection with my postings.                       |
+-----------------------------------------------------------------------------+ 
Byron Han, Communications Architect      Cereal, anyone?  :-)  A1!
Apple Computer, Inc.                     -------------------------------------
20525 Mariani Ave, MS27Y                 Internet: han@apple.COM
Cupertino, CA 95014                      UUCP:{sun,voder,nsc,decwrl}!apple!han
--------------------------------------   GENIE: BYRONHAN
ATTnet: 408-974-6450   Applelink: HAN1   CompuServe: 72167,1664
------------------------------------------------------------------------------