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From: billwolf@hubcap.clemson.edu (William Thomas Wolfe,2847,)
Newsgroups: comp.lang.ada
Subject: Re: Garbage Collection
Message-ID: <4073@hubcap.UUCP>
Date: 12 Jan 89 02:43:28 GMT
References: <35340@think.UUCP>
Sender: news@hubcap.UUCP
Reply-To: wtwolfe@hubcap.clemson.edu
List-Id: <comp.lang.ada>

>From article <35340@think.UUCP>, by barmar@think.COM (Barry Margolin):
> 3 million people aren't editing and
> compiling the same file, but one user is, and he may tell the command
> processor to delete the compiler warnings before he's finished
> scanning through them in the editor (because he doesn't want them
> cluttering up the database if he asks for other compiler warnings to
> be displayed).

    Why doesn't the editor do the deletion of warnings?  If the editor
    is already providing a "search for next warning" function, it should
    provide the "delete warning" function as well.  Then we wouldn't have
    to deal with shared variables at all, although your later comments do
    make the whole question moot.

> Real-time GC mechanisms are defined to do a bounded amount of work PER
> ALLOCATION.  [....]  And generational and ephemeral GC mechanisms
> concentrate their efforts on memory most likely to contain garbage.

    Could you send me a detailed explanation of these mechanisms?

> Decent GC mechanisms can be told to ignore manually managed space.  

    If this means that I can specify that my allocation requests carry
    the condition that the GC mechanism will stay away from the space
    I receive, then I'll be happy to change my position on garbage collection.

    (Erland, you may have spoken too soon!)

    HOWEVER.  There are still things that need changing.  There still needs
    to be implicit destruction of local environments via calls to DESTROY
    routines.  Parameter passing is still ambiguous with respect to storage
    utilization.  In general, I can live with GC being required IFF I can
    also exert total control over when, how, and for how long every piece
    of space is occupied, and I can determine exactly how much space is
    being used implicitly and for how long.  

    If what you say is true, then nothing prevents me from designing an 
    entire system in which GC is completely absent and for which I can make 
    firm statements regarding the system's time and space characteristics; 
    even though the compiler is required to provide GC for those who wish
    to use it, the programmer can require the compiler to provide a
    local environment in which GC is prohibited.  This I can live with.  



                                              Bill Wolfe

                                       wtwolfe@hubcap.clemson.edu