Re: [9fans] Re: advantages of limbo

[David Presotto <presotto@closedmind.org>]

> Does that mean that designers of Inferno windowing system were
> required to avoid using cyclic references in window structures?
> That is, a window does not know who its creator is? 

Yup, as long as something had a reference to the window, the window stayed
around.  If the reference is in  cyclic struct that becomes unreachable,
it will get collected.  However the immediacy that users expect is lost.

> It's a decision. But a limiting one. Influenced by an implementation.
> Just running garbage collector with limited scope would do it
> without limitations.

All decisions are limiting.  You pay extra for limited
scope just as you do for reference counting.  If you limit the scope
small enough that you release things as quickly, then you have
the equivalent of reference counting with higher cost.

>  It was not a tradeoff of normal garbage collection. Fixed-time garbage
> collection techniques existed long before java. It was just an early
> implementation to make it running.

We lived with this 'just to make it running' for several years.  The jdk's
now contain multiple gc techniques including fixed time ones.  From outside
the VM the two are indistinguishable unless you care when the memory is
freed, i.e., if when the freeing is visible.  That happens both in  java
and in limbo if the finalize routines can have extrernally visible effects.

> Is there any other reason reference loops are not very common amongs
> limbo programmers besides limitations of the garbage collector?

The garbage collector has little influence on our programming of cyclic
structs, expecially since the gc correctly collects those cycles when they
are freed.  However, people seem to understand dags better then cyclic
structures and make less mistakes manipulating them, so they use them more often.