Subj : Exceptions and Object Lifetimes
To   : netscape.public.mozilla.jseng
From : "Pete Diemert" <pete.diemert@purposebuilt.com.au>
Date : Wed Dec 17 2003 11:16 am


Hello, this is my first post to this group, if I am posting in the wrong
place please let me know.  We have been working to embed the Spidermonkey
1.5 engine with great progress however there are a couple of issues that
have sprung up which I can't seem to locate the answers for:

1)  Exceptions - We have exposed our own object/funcs and so, would also
like to expose errors that our functions can generate as catchable
exceptions in JS.  However, from looking at JSAPI.H we cannot see a clear
way to "throw" an exception from the host.  We have tried to add entries to
JS.MSG and marked them as JSXN_ERR which seems to cause the exception object
to get generated in scope but alas nothing is catching in JS.  Do we have to
actually construct JS script to do the throw then evaluate the script in
scope in order to get exceptions?

2)  Object Lifetimes - To make the object model in JS coherent with our own
internal object model we allow the JS object to keep a "reference count" on
our internal object so that JS controls its lifetime.  This works fine but
we notice that the GC is VERY lazy and will choose to keep objects alive
after they are clearly never going to be accessed again, waiting for
shutdown or mem threshold, e.g.:

function foo()
{
    var x = new SomeObject;
    // x drops out of scope after func, never to be seen again but object
ref will remain
}

The object does indeed get cleaned up at shutdown but we have a system that
may instantiate some fairly big footprint objects such as forms, databases,
recordsets, etc...  Understanding that the GC reserves the right to
arbitrarily clean these objects is there some way we can get a callback
stating "object no longer in use by any call object" in lieu of a
JSFinalize() so that we can force the GC ourselves and prevent a rather
large uneeded working set?

Any insight or pointers in the right direction would be helpful including
more searchable resources like this newsgroup.

thanks,
Pete Diemert

.