Path: utzoo!attcan!uunet!mcsun!sunic!bmc!bio.embnet.se!mats
From: Mats.Sundvall@bio.embnet.se
Newsgroups: comp.sys.mac.programmer
Subject: HLock and Think C 4.0
Message-ID: <18.25645e4f@bio.embnet.se>
Date: 17 Nov 89 18:38:55 GMT
Organization: Embnet node in Sweden at Biomedical Center, University of Uppsala, Sweden
Lines: 27

Just got bit by not locking a handle!

Please correct me if I am totally wrong but this is what I think happend.
But my diagnose raised a couple of questions.

In Think C 4.0 I define an object CTime as a instance of CObject. It has some
integer fields and one Str255 field. The method Setstring does a strcpy
from the parameter to the field.

So I compile and run the program, the first time I does a CList::Setstring
the string is empty. The second time the string is there.

When tracing the code I notice that the memory location for CList->mystring
is moved, probably because the ANSI library is moved into memory.
So I do a HLock on the CTime object and unlock it after I have done the
strcpy. It works.

Then I locked through the object library to see if this is the method that
Think uses. I was surprised when I did not find that many HLock in their
code. One difference when they copy strings is that they copy pstrings
with CopyPString (that does a Blockmove). Is it safe to do a Blockmove
without locking the handle? I would expect that many more HLocks should be in
the code.

	Mats Sundvall
	University of Uppsala
	Sweden