Pointers in Slate.

[Todd Fleming]

Brian Rice wrote:

> About finalizers, yes. Resources should be pushed into a collection 
> whose elements are then re-initialized (mostly opened) on the next 
> startup, as well as of course being closed on shutting down.


I was thinking about it a little differently. An open file does no good 
if it isn't being used by something. The closest way I know if to model 
"use" is that something is pointing to it. So, if nothing is pointing at 
an open file object, it would be nice if the GC eventually closes the file.

Example: a read stream is opened on a file. The read stream is given to 
something that uses read streams, but doesn't know that it needs to 
close the stream when it's done. Instead it just "forgets" the stream 
and the GC eventually calls a finallizer which closes the file.

There are some problems with this. Some OS's (Linux) limit how many file 
descriptors a process may have open. When the limit is reached, you 
could trigger a full GC and try again. Unfortunately, Linux also has a 
limit on how many file descriptors are open across the entire system, so 
this would mean the process doesn't play well with others. Other OS's 
(Windows) don't have an open-file limit (other than memory of course), 
but keep locks on the file until it is closed. You can use non-exclusive 
locks in Windows, but most applications use exclusive locks, so they 
would be prevented from opening a file that is still hanging around in 
Slate unused.

There are probably other external resources which don't have these 
problems and would benifit from not having to manually free them.

Todd