Re: Historical Implementations to Garbage Collectors

  "Kaz Kylheku" <kaz@kylheku.com>
> On 2014-05-04, Robin Vowels <robin51@dodo.com.au> wrote:
>>: <lpsantil@gmail.com> wrote:
>>> I'm interested in studying historical implementations of garbage
>>> collection in early programming languages (BASIC, Lisp, etc). I'm
>>> especially interested in language/runtime interface descriptions.
>>> Does anybody have references they can share?
>>
>> McKeeman, Horning, and Wortman's XPL compiler used garbage
>> collection for strings on S/360. Collection was automatic
>> and invisible to the user.
>>
>> No tags were needed.
>
> Why would there be tags;


I mentioned it only only because John mentioned tags in one implementation
that he cited.


> strings don't point to other strings. There are no
> arcs or cycles in the graph. You never have to solve the problem "has the
> garbage collector already visited this string", since you can use a handles to
> keep track of strings---hence there is no need to walk the graph of non-string
> objects in order to find strings; just the array or list of string handles,
> where no two handles reference the same string.


In the XPL implementation, multiple references [handles] to the same string can occur.
Furthermore, strings can overlap; that is, two or more handles can point to
different parts of the same string.


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