Re: destroy and garbage collection

[Per Bothner <per at bothner dot com>]

On 05/27/2010 02:07 AM, teong leong chuah wrote:
> Hi Per,
>
> Can you explain how objects in kawa are destroyed or set as
> unreferenced and waiting for garbage collection?

I'm not sure what you're asking for, beyond explaining
garbage collection, which you seem to know about.

http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-8.html#node_sec_5.10

> This works in general but what I haven't figure out is how to destroy
> objects in kawa. We would typically have many such objects store in a
> scheme list or a hashtable and we've been doing (set! mylist '()) or
> empty the hashtable.
>
> Does that ensure the deletion of such objects that were previously
> inside the list?

Essentially.  You don't "destroy" or "delete" objects in Kawa (or Java),
but they get garbage-collected when unreachable.  So you may sometimes
explicitly need to some object unreachable, typically by nulling (or niling)
the variable(s) that refer to the object.

> We have our own thread object that is created using a loop, a sleep
> and future to create a periodically firing thread that execute a
> procedure. We've put threads inside our objects and it seems with, the
> thread still firing and running, the objects that have been emptied
> from the list are still alive.

This is rather too vague to say much.

But note there is nothing guaranteed about garbage collection
deleting objects - if there is enough memory it is quite possible
garbage collection will never get around to deleting the objects -
because there is no need to.  Especially "older" objects are less
likely to be deleted, because a generational garbage collection
will focus on deleting "young" garbage (i.e. relatively
recently-created objects), and never get around to deleting
older garbage - because just deleting the younger objects is
good enough.

> If I stop the thread there wouldn't be
> any way of knowing whether my objects are alive or not.
>
> Can you walk me through the scheme way of destroying objects?

There is nothing Scheme-specific about Kawa GC - it's just the Java garbage
collector.
--
	--Per Bothner
per@bothner.com   http://per.bothner.com/