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https://issues.apache.org/jira/browse/QPIDJMS-552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17441108#comment-17441108
 ] 

ASF GitHub Bot commented on QPIDJMS-552:
----------------------------------------

franz1981 commented on a change in pull request #44:
URL: https://github.com/apache/qpid-jms/pull/44#discussion_r745530285



##########
File path: 
qpid-jms-client/src/main/java/org/apache/qpid/jms/JmsConnectionFactory.java
##########
@@ -368,6 +377,19 @@ protected static URI createURI(String name) {
         return null;
     }
 
+    protected Supplier<Holder<ExecutorService>> 
getCompletionExecutorServiceFactory() {
+        if (this.completionThreads == 0) {
+            return null;
+        }
+        synchronized (this) {
+            if (completionExecutorServiceFactory == null) {
+                QpidJMSForkJoinWorkerThreadFactory fjThreadFactory = new 
QpidJMSForkJoinWorkerThreadFactory("completion thread pool", true);
+                completionExecutorServiceFactory = sharedRefCnt(() -> new 
ForkJoinPool(completionThreads, fjThreadFactory, null, false), 
ThreadPoolUtils::shutdown);

Review comment:
       > Given that, the mechanism still all seems rather overcomplicated. This 
feels like a relatively simple case, an 'if there is an existing pool, then use 
that, otherwise create one' check coupled with the opposing cleanup. One that 
should be relatively infrequently used. It seems like even a simple 
synchronized block with a count inside could do?
   
   Not sure, there's still a problem related disposing it: 
   
   1. the shared/common pool should be allocated once and live forever?
   2. if the answer to 1 is no, how/what is going to trigger disposing it?
   
   The mechanism I've implemented just handle this use-case using reference 
counting, but in order to do it, it requires a someone to be the first owner, 
but at least ensure correct release of resources that could cause the whole 
application/class-loader to leak 




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> JMS 2 Completion threads shouldn't scale with the number of sessions
> --------------------------------------------------------------------
>
>                 Key: QPIDJMS-552
>                 URL: https://issues.apache.org/jira/browse/QPIDJMS-552
>             Project: Qpid JMS
>          Issue Type: Bug
>          Components: qpid-jms-client
>    Affects Versions: 1.3.0
>            Reporter: Francesco Nigro
>            Priority: Major
>
> JMS 2 Completion threads are now tied to be one per JMS Session ie a client 
> application with N JMS sessions need N completion threads to handle the 
> completion events.
> Given that the asynchronous model of JMS 2 allows users to have few threads 
> handling many JMS sessions, should be better to reduce the amount of 
> completion threads without exceeding the number of available cores and 
> shrink/grow according to the completion event processing load.
> If the user confine a connection in a thread handling many JMS sessions and 
> the completion events are issued by the same Netty thread in sequence, if the 
> completion processing for a JMS Session is fast enough, next JMS Sessions can 
> reuse existing completion threads instead of using a new one.
> This model save using too many completion threads for users tasks that are 
> supposed to be very fast: if the user task cause a specific JMS Session 
> completion thread to block, the expectation is that the system should be able 
> to create a new completion thread to handle other JMS Session completion 
> events, as expected.



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