On Jul 10, 2006, at 12:41 PM, Oscar Maire-Richard wrote:
Hi,
I would like to know your suggestions for what I think is a common
problem:
For each request my application obtains an identifier (that is not
the PK but must be unique), if a DataObject with this identifier
exists, uses it, other case creates a new one; does some processing
(with other DataObjects) and commits all. I am using a data context
per session.
My problem is how to avoid DataObjects with duplicated identifiers
when several sessions send requests simultaneously.
An obvious solution is to synchronize the whole process until the
commit is done, however the processing requires a long time, and I
would like to parallelize to improve performance.
Thanks,
Oscar
Is identifier something that is derived from request values?
In any event you'll have to do synchronization. Just need to make it
smart, so that it only locks out the threads that access the same
identifier. This means that identifier instances themselves are the
prime candidates to work as synchronization objects.
For example you can have an application-scoped HashMap that keeps
currently processed identifiers. So a request filter may look like this:
String id = ... // generate id
Map ids = ... // get an application shared map
String lockId;
synchronized(ids) {
// make sure that we do not override a matching identifier
lockId = (String) ids.get(id);
if(lockId == null) {
lockId = id;
ids.put(id, id);
}
}
synchronized(lockId) {
// do processing
}
Replacing HashMap with some sort of LRUMap (such as the one in
Jakarta commons-collections) should prevent unlimited memory growth.
Andrus
