Re: [Jython-dev] Problems with weak references?

[<Ric...@i2...>]

Hi Samuel,

(Apologies if the formatting of this message is bizarre, we've been
forced onto Lotus Notes and I can't get it to stop chopping up my lines
in unpredictable places).

Anyhow, I had some more time to look into the problem.

In InternalTables2 you are storing a PyBeanEventProperty reference
into a HashMap, and this seems to prevent garbage collection.

If I change the implementation like so, the memory leak is closed:

    protected WeakHashMap adapters;

    protected Object getAdapter(Object o,String evc) {
        HashMap ads = (HashMap)adapters.get(Integer.toString(o.hashCode
()));
        if (ads == null) return null;
        return ads.get(evc);
    }

    protected void putAdapter(Object o,String evc,Object ad) {
        HashMap ads = (HashMap)adapters.get(Integer.toString(o.hashCode
()));
        if (ads == null) {
            ads = new HashMap();
            adapters.put(Integer.toString(o.hashCode()),ads);
        }
        ads.put(evc,ad);
    }

Or, alternately, I think you can do the following:

    protected WeakHashMap adapters;

    protected Object getAdapter(Object o,String evc) {
        String key = evc + "$" + o.hashCode();
        return adapters.get(key);
    }

    protected void putAdapter(Object o,String evc,Object ad) {
        String key = evc + "$" + o.hashCode();
        adapters.put(key,ad);
    }


Rich




                                                                                           
                    "Samuele                                                               
                    Pedroni"             To:     <jyt...@li...>,       
                    <pedroni@inf.        <Ric...@i2...>                              
                    ethz.ch>             cc:                                               
                                         Subject:     Re: [Jython-dev] Problems with weak  
                    01/17/01             references?                                       
                    04:42 PM                                                               
                                                                                           
                                                                                           




Hi.

First of all it seems (but maybe I'm missing something) that java.awt leaks
memory too or at least
to discard things at non-predictable points:
>>> C:\WINDOWS>\jython\mjyth
Jython 2.0beta2 on java1.3.0 (JIT: null)
Type "copyright", "credits" or "license" for more information.
>>> from java.lang import System,ref
>>> from java import awt
>>> f=awt.Frame()
>>> b=awt.Button()
>>> f.add(b);f.pack();f.show()
java.awt.Button[button0,0,0,0x0,invalid,label=]
>>> 0 # clears _
0
>>> w=ref.WeakReference(b)
>>> del b
>>> f.remove(w.get())
>>> System.gc(); System.gc()
>>> w.get() # leak? why?
java.awt.Button[button0,4,28,136x23,label=]
>>> 0
0
>>> f.dispose()
>>> del f
>>> System.gc()
>>> w.get()
>>>
f.remove() + System.gc() seems not enough in order to discard b?
This is related to the tables because as long as b is around, its adapters
will
be too.

Indipendently of this: the table can leak memory in some cases (it should
be
possible to fix this but after 2.0):
Jython 2.0beta2 on java1.3.0 (JIT: null)
Type "copyright", "credits" or "license" for more information.
>>> from java import awt
>>> import itd
>>> from java.lang import System
>>> b=awt.Button(); b.actionPerformed = lambda e: b
>>> itd.ad()
['java.awt.event.ActionListener']
>>> del b
>>> System.gc()
>>> itd.ad()
[]
>>> # no leaks with this code but
>>> b=awt.Button(); b.actionPerformed = lambda e,me=b: None
>>> itd.ad()
['java.awt.event.ActionListener']
>>> del b
>>> System.gc()
>>> itd.ad()
['java.awt.event.ActionListener']
>>> # so we get a memory leak
In this case the listener function hold a ref to the source object, to
solve
this the table should (carefully) use weak-refs for values
too. In the meantime this kind of code can be avoided given that events
come
with source info.

regards, Samuele Pedroni.