Thanks Stephan,
I already print out the list's contents, the elements's oid and type are
the same,
but the objects are unreachable.
Same oid because those weak references belong to same L1 entry, no problem
here.
Let's consider a Level1Entry contains two Level2Entry: l2_1, l2_2.
if l2_1, l2_2 have same type, l1.get(l2.getType()) will return l2_1
because l1.get will return the first element match the type.
// must only be called while synchronized on map:
public Level2Entry get(Type type) {
for (Iterator i = list.iterator(); i.hasNext();) {
Level2Entry l2 = (Level2Entry) i.next();
* if (l2.getType().equals(type)) {*
return l2;
}
}
return null;
}
but if when cleanUp was called, the unreachable object is l2_2, the
condition
(l1.get(l2.getType()) == l2) in cleanUp function will not be met.
I think this is the problem we have, you can see the list will keep growing
after this.
-Huai Dong
On Mon, Nov 23, 2009 at 8:15 PM, Stephan Bergmann
<[email protected]>wrote:
> On 11/23/09 07:58, Huaidong Qiu wrote:
>
>> Hi all,
>>
>> We got a problem like this, one of the L2 entry list keep growing consume
>> too much memory.
>>
>> module jurt
>>
>> package com.sun.star.lib.uno.
>> environments.java;
>>
>> the cleanUp member function of class Registry.
>>
>> // must only be called while synchronized on map:
>> private void cleanUp() {
>> for (;;) {
>> Level2Entry l2 = (Level2Entry) queue.poll();
>> if (l2 == null) {
>> break;
>> }
>> // It is possible that a Level2Entry e1 for the OID/type
>> pair
>> // (o,t) becomes weakly reachable, then another Level2Entry
>> e2
>> // is registered for the same pair (o,t) (a new Level2Entry
>> is
>> // created since now e1.get() == null), and only then e1 is
>> // enqueued. To not erroneously remove the new e2 in that
>> case,
>> // check whether the map still contains e1:
>> String oid = l2.getOid();
>> Level1Entry l1 = getLevel1Entry(oid);
>> if (l1 != null && l1.get(l2.getType()) == l2) {
>> removeLevel2Entry(oid, l1, l2);
>> }
>> }
>> }
>>
>> All those weak reference Level2Entry entries are invalid, the condition
>> (l1.get(l2.getType()) == l2) keeps cleanUp function from removing them
>> from
>> the list.
>>
>> I think if this
>> // It is possible that a Level2Entry e1 for the OID/type
>> pair
>> // (o,t) becomes weakly reachable, then another Level2Entry
>> e2
>> // is registered for the same pair (o,t) (a new Level2Entry
>> is
>> // created since now e1.get() == null), and only then e1 is
>> // enqueued.
>> happened once then there is no way the condition (l1.get(l2.getType()) ==
>> l2) can be true again, because get(l2.getType()) always return the first
>> element in the list, but queue.poll() return the newly released weak
>> reference which can not be the first one in the list.
>>
>
> I fail to see a flaw in the current algorithm. In the simplest case,
> consider a Level1Entry L that has just one Level2Entry E (for some object O,
> OID D, type T) in its list. Suppose o1 has become unreachable and cleanUp
> is called: l2 will be bound to E; oid will be bound to D; l1 will be bound
> to L; l2.getType() returns T; l1.get(l2.getType()) returns E, so
> removeLevel2Entry will be called and will indeed remove E from L's list (and
> will actually also remove L from the map of Level1Entries).
>
>
> If weak reference list cleanup mechanism is correct, could please give
>> some
>> possible reasons could cause the growing problem of L2 entry list.
>>
>
> You mean, you observe a specific instance of Level1Entry whose list of
> Level2Entries keeps growing without bound? That sounds strange. First, all
> entries in the list should be for different UNO types supported by the
> respective UNO object, so that should bound the length of the list (no UNO
> object probably supports more than a few dozen different UNO types).
> Second, the only way to have more entries in the list would be to have
> entries referencing different reachable Java objects which would
> nevertheless all have the same UNO OID. That would sound like a bug
> somewhere.
>
> Maybe you can add debug code to print, for each Level2Entry E in the list
> of the given problematic Level1Entry, the following:
> - E.toString()
> - E.getOid()
> - E.getType()
> - E.get()
> to get an idea what that growing list looks like.
>
> -Stephan
>
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