Re: Immutable Datastructures with good Sharing

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 05 Nov 2011 16:20:12 -0400

Message-ID:

<4eb59a7e$0$292$14726298@news.sunsite.dk>

On 11/5/2011 2:52 PM, Jan Burse wrote:

Eric Sosman schrieb:

Out of curiosity, why do you want an immutable queue? What
problem are you trying to solve?

Well it has to be seen in the context of garbage collection.
For example the immutable stack can have a good performance.

> For push you just grab a new stack cell from the heap.
>
> When you pop and you have no other pointers to the stack itself
> anymore in the application, then cells become eligible to
> garbage collection and will quickly reenter the heap and
> thus again be available for the application.

I would expect worse performance with typical stack operations.

In the current situation at hand, you can imagine that
some pointers to the datastructure will nevertheless
still remain, so that I can kind of have a historical
view of what happened with the stack.

This historical view is easiest implemented by an immutable
data structure, but its performance hinges on the fact how
good the sharing works. Same holds for the queue. If a push()
were to copy the full stack I would get a lame application.

Yes.

But will the time you spend investigating this really cost less
than what it cost to buy 4 GB more RAM and just clone the objects
you want to store as history.

Arne