Path: utzoo!attcan!uunet!lll-winken!ames!mailrus!eecae!cps3xx!rang
From: rang@cpsin3.cps.msu.edu (Anton Rang)
Newsgroups: comp.sys.mac.programmer
Subject: Re: serious code generation bug in Lightspeed C
Message-ID: <1532@cps3xx.UUCP>
Date: 15 Jan 89 17:50:27 GMT
References: <6275@hoptoad.uucp> <1676@helios.ee.lbl.gov> <6315@hoptoad.uucp>
Sender: usenet@cps3xx.UUCP
Reply-To: rang@cpswh.cps.msu.edu (Anton Rang)
Organization: Michigan State University, Computer Science Dept.
Lines: 33
In-reply-to: tim@hoptoad.uucp's message of 15 Jan 89 12:18:10 GMT

In article <6315@hoptoad.uucp> tim@hoptoad.uucp (Tim Maroney) writes:
>   It is silly to say that this is a well documented problem.  I've read
>   three drafts of Inside Mac, starting with the loose-leaf binder edition
>   unfathomable aeons ago, and that an assignment could require locking
>   has never been explicitly mentioned.

  Well, maybe not *well* documented, but documented at least.  From
Inside Mac, volume II, page 16:

    The Lisa Pascal compiler frequently dereferences handles during
    its normal operation.  You should take care to write code that
    will protect you when the compiler dereferences handles in the
    following cases:

	[ ... ]

    Assigning the result of a function that can move or purge blocks
    (or of any function in a package or another segment) to a field in
    a record referred to by a handle, such as

	aHandle^^.field := NewHandle(...)

    A problem may arise because the compiler generates code that
    dereferences the handle before calling NewHandle--and NewHandle
    may move the block containing the field.

  Maybe this should have been emphasized more, but it was at least
mentioned (otherwise I probably would have run into it before).

+---------------------------+------------------------+----------------------+
| Anton Rang (grad student) | "UNIX: Just Say No!"   | "Do worry...be SAD!" |
| Michigan State University | rang@cpswh.cps.msu.edu |                      |
+---------------------------+------------------------+----------------------+