AmiraTalbi
You exactly understand the problem... and you are right, it is not specifically
a jBpm issue. There is a resource (the process instance) that needs to be
"used/updated" by each thread in turn, not all at once.
The reason I did not want to use your suggestion is that I think that this
would block all traffic... In 60 seconds I may have 1,000 incoming
events/threads, destined for 950 different process instances. In the vast
majority of cases there is no contention and i could, in theory, process 950
process instances in parallel... with only 50 blocking.
The only solution that I can think of is to either use the jBpm lock facility
OR to have an external locking process.
1) Using the jBpm lock facility
| long pid = 123;
| JbpmContext jC = jbpmConfiguration.createJbpmContext();
| try {
| ProcessInstance pI =
jC.loadProcessInstanceForUpdate(pid);
|
pI.getRootToken().lock(Thread.currentThread().toString());
| }
| finally {
| jC.close();
| }
| try {
| ProcessInstance pI =
jC.loadProcessInstanceForUpdate(pid);
|
pI.getRootToken().unlock(Thread.currentThread().toString());
| pI.signal();
| }
| finally {
| jC.close();
| }
|
The problem with this is it is pretty heavyweight (in terms of database updates
done) and also I have to write a fair chunk of code to deal with threads that
die without releasing their lock etc etc etc.
2) Implementing a a lock facility using the database, for example mysql SELECT
GET_LOCK('lock1',10)
The problem with this is that I need to ensure that no thread attempts to
acquire a process instance without first getting a lock.
Unfortunately the solution is multi node, so I am not able to do in memory
locking easily.
I had hoped that jBpm might have a clever way of achieving this without me
having to write any code. At an abstract level I believe that this problem is
similar to a process instance reaching a task node whose task could be
performed by multiple actors. Presumably in this case jBpm has some mechanism
to prevent multiple actors fulfilling the task.
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http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4196919#4196919
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