Path: utzoo!attcan!uunet!midway!mimsy!mojo!russotto
From: russotto@eng.umd.edu (Matthew T. Russotto)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Speaking of Munger...
Message-ID: <1990Jul13.142801.6843@eng.umd.edu>
Date: 13 Jul 90 14:28:01 GMT
References: <233@sun13.scri.fsu.edu> <42917@apple.Apple.COM>
Sender: news@eng.umd.edu (The News System)
Organization: College of Engineering, Maryversity of Uniland, College Park
Lines: 70

In article <42917@apple.Apple.COM> keith@Apple.COM (Keith Rollin) writes:
>In article <233@sun13.scri.fsu.edu> pepke@gw.scri.fsu.edu (Eric Pepke) writes:
>>Speaking of Munger, it's a cute little routine, but what happens when it 
>>fails due to insufficient memory?
>>
>>I run this little test program: 
>>
>>#include <stdio.h>
>>#include <MacTypes.h>
>>#include <MemoryMgr.h>
>>
>>main()
>>{
>>    unsigned char buffer[1000];
>>    Handle block;
>>    long beforeLength, afterLength;
>>    
>>    printf("Yahoo!\n");
>>    
>>    block = NewHandle(0L);
>>        
>>    for (;;)
>>    {
>>        beforeLength = GetHandleSize(block);
>>        Munger(block, GetHandleSize(block), (unsigned char *) 0, 
>>                0L, buffer, (long) sizeof(buffer));
>>        afterLength = GetHandleSize(block);
>>        
>>        if (beforeLength + sizeof(buffer) > afterLength || MemError())
>>        {
>>            printf("\nSize increased from %ld to %ld\n", 
>>                    beforeLength, afterLength);
>>            printf("MemError() == %d\n", MemError());
>>            exit(-1);
>>        }
>>        else
>>        {
>>            printf(".");
>>        }
>>    }
>>}
>>
>>and I get
>>
>>Yahoo!
>>...........................................................................
>>.....
>>...........................................................................
>>.....
>>...........................................................................
>>.....
>>.......................................................................
>>Size increased from 311000 to 311000
>>MemError() == 0
>>
>>So, when Munger fails due to lack of memory, you cannot tell from looking 
>>at MemError.  In this case, at least, it left the handle unchanged.  Can 
>>somebody who knows about the internals of Munger tell me if that is 
>>guaranteed to be the case, or is there a possibility that the handle will 
>>be corrupted in any way, such as being left larger than it was but not as 
>>large as is needed?
>
> [detailed, but, except on the 64K ROMs, incorrect explanation...Sorry Keith]

The real reason your MemError() test is failing is that printf uses the memory
manager, and that clears MemErr (because the calls printf makes succeed)
--
Matthew T. Russotto	russotto@eng.umd.edu	russotto@wam.umd.edu
][, ][+, ///, ///+, //e, //c, IIGS, //c+ --- Any questions?
		Hey!  Bush has NO LIPS!