[rules-users] Multi Access to Stateful Session
Wolfgang Laun
wolfgang.laun at gmail.com
Tue Apr 3 02:38:40 EDT 2012
The propositions were meant to investigate the possibility of some
synchronization problem in Drools.
However. For embedding Drools in a multi-threaded application with several
threads needing to insert facts I'd probably still go for Drools being run
by one or two threads, with a BlockingQueue for feeding facts to the
(single) thread doing insertions. Either call fireAllRules() whenever the
queue is empty (peek()==null) or use fireUntilHalt() in another thread. (I'd go
for the first options. It dissolves all synchronization issues...)
-W
On 03/04/2012, gboro54 <gboro54 at gmail.com> wrote:
> I will give these a try although they would seem to defeat the purpose of
> having the ability to have a session always up and running already
> evaluation. Another thought I had was to get rid of the list of deregistered
> positions and instead create a lightweight fact which would just get created
> an inserted(i.e DeregisteredMessageFact). This would allow the single
> threaded session to own the controller completely. Does this sound like a
> reasonable approach to the problem?
>
>
> laune wrote
>>
>> Another poster on this list has stated that there are flaws in the
>> synchronization of Drools, but IIRC this was related to an older
>> version.
>>
>> I can propose two additional experiments:
>>
>> (1) Have you ever run this with insertions from a single thread, and with
>> the
>> engine being run in one other thread?
>>
>> (2) Run an experiment where you call fireAllRules() after each
>> insertion, with insertions from multiple threads.
>>
>> -W
>>
>>
>> On 02/04/2012, gboro54 <gboro54@> wrote:
>>> I updated the MessageControl fact as follows and the same issue still
>>> occurs:
>>>
>>> private Long currentPosition = new Long(0);
>>> private Set<Long> excludedPositions = new HashSet<Long>();
>>>
>>> public synchronized void addPositionToExclusionList(Long position) {
>>> excludedPositions.add(position);
>>> }
>>>
>>> public synchronized Long getCurrentPosition() {
>>> return currentPosition;
>>> }
>>>
>>> public synchronized void moveCurrentPositionForward(Integer value) {
>>> currentPosition += value;
>>> if (currentPosition % 20000 == 0) {
>>> System.out.println(currentPosition);
>>> }
>>>
>>> }
>>>
>>> public synchronized boolean atExcludedPosition() {
>>> return excludedPositions.contains(currentPosition);
>>> }
>>>
>>> Not sure what else could occur between the insertions and the rule
>>> execution
>>> that would be an issue...
>>>
>>>
>>> laune wrote
>>>>
>>>> So it looks like a race condition.
>>>>
>>>> There is one chink in the snchronizing armour of class MessageControl.
>>>> The Map excludedPositions (although in itself synchronized on its own
>>>> lock) is exposed via the getExcludedPositions. Thus, synchronization
>>>> between currentPosition and excludedPositions is broken. I can't say
>>>> whether this matters, but just try and add delegating methods to
>>>> MessageControl and remove getExcludedPositions. (And use a plain
>>>> HashSet - synchronization is provided by MessageControl.)
>>>>
>>>> Obviously, rules will have to use something like
>>>> atExcludedPosition == true
>>>> when the Map is fully privatized.
>>>>
>>>> -W
>>>>
>>>>
>>>> On 02/04/2012, gboro54 <gboro54@> wrote:
>>>>> A gap would have to occur somewhere but I am not sure how or why.
>>>>> Since I am using the same data for each test case, the outcome should
>>>>> be the same but 75% of the time to position stops at a random point
>>>>> and thus allows messages to backup in memory
>>>>>
>>>>> On Mon, Apr 2, 2012 at 12:19 PM, laune [via Drools]
>>>>> <ml-node+s46999n3878174h55 at .nabble> wrote:
>>>>>> What is the current position value in the controller when it blocks? A
>>>>>> regular message rank or one of those not to be processed or both?
>>>>>>
>>>>>> Are you sure that message ranks are increasing without gaps except
>>>>>> those in the excluded position map?
>>>>>>
>>>>>> -W
>>>>>>
>>>>>> On 02/04/2012, gboro54 <[hidden email]> wrote:
>>>>>>
>>>>>>> Forgo to mention each time a position is added to the excluded
>>>>>>> position
>>>>>>> map,
>>>>>>> the insertOrUpdate method is called on the session wrapper.
>>>>>>>
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>>>>>
>>>>>
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