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From Tim Ellison <t.p.elli...@gmail.com>
Subject Re: Some questions about the architecture
Date Mon, 31 Oct 2005 17:27:21 GMT
Archie Cobbs wrote:
> Mark Wielaard wrote:
>> On Thu, 2005-10-20 at 17:56 -0500, Archie Cobbs wrote:
>>> Off tanget, but IMHO this is not strictly true: it depends on whether
>>> VM native code relies on finalize() to free up its (non-heap) memory.
>>> Here's an exmaple of this:
>>>   http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4797189
>> That problem doesn't occur with GNU Classpath since our zip
>> implementation is written in java itself. But we have a similar example
>> in the mauve testsuite (one that I also observed while getting JBoss to
>> work with GNU Classpath and JamVM). There is a test that opens lots of
>> FileInputStreams and then expects the garbage collector to finalize
>> these and free up the open file descriptors. gcj explicitly handles this
>> by forcing a garbage collect and finalization pass when it cannot create
>> a new file descriptor. We currently don't have any convention for
>> marking VMObjects or finalizers as (scarce) holding native resources or
>> make the native code signal the runtime to do a finalization of such
>> objects.
> Right, and so this is a bug (although in a different form than
> the ZIP example above) in Classpath too. It could be fixed

I think it is unfair to describe this as 'a bug'.  The FileInputStream
has a lifecycle (from open() to close()) that users are expected to
follow.  While in this case you could image a VM knowing about the file
handle resources and trying to free them using finalization, such a fix
only inches you towards a fuller automatic resource management.  There
are still many other areas (SQL cursors, window handles, etc.) that have
to be explicitly managed by the application.

In this case, it is reasonable to perform a safety-check on
finalization, but there are lots of reasons already well documented why
you should not rely on finalization.

Just my 2c.


> by creating a new VM method e.g. VMRuntime.runFinalizers()
> that would "try hard" to run finalizers.. then the other thread
> could loop, calling this method each iteration. There might still
> be some more subtlety to this (finalizers have not guarantee of
> returning quickly, etc.)
> -Archie
> __________________________________________________________________________
> Archie Cobbs      *        CTO, Awarix        *      http://www.awarix.com


Tim Ellison (t.p.ellison@gmail.com)
IBM Java technology centre, UK.

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