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https://issues.apache.org/jira/browse/HTTPCORE-750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17729404#comment-17729404
 ] 

Michael Osipov commented on HTTPCORE-750:
-----------------------------------------

[~Gaojie_Liu], maybe you can incentivize [~olegk] with some amount to do the 
release ASAP.

> H2ConnPool creates too many conns under high load at initialization time
> ------------------------------------------------------------------------
>
>                 Key: HTTPCORE-750
>                 URL: https://issues.apache.org/jira/browse/HTTPCORE-750
>             Project: HttpComponents HttpCore
>          Issue Type: Bug
>          Components: HttpCore
>    Affects Versions: 5.2.1
>         Environment: Linux / Ubuntu / openjdk version "1.8.0_292"
>            Reporter: Gaojie Liu
>            Priority: Major
>             Fix For: 5.2.2
>
>          Time Spent: 50m
>  Remaining Estimate: 0h
>
> We are using httpcore5 5.2.1 and we observed that at application startup 
> time, httpclient5 could create more than 1 conn per endpoint and in some 
> cases, too many connections caused OOM issue since httpclient5 creates a pair 
> of input/output buffer per conn.
> The regression is introduced by HTTPCORE-750, which made this change:
> [https://github.com/apache/httpcomponents-core/commit/14caf43eae407c544161c7f92329e8beb42a3534]
>  
> {code:java}
>  if (poolEntry.session != null) {
>                 callback.completed(poolEntry.session);
>             } else {
>                 poolEntry.requestQueue.add(callback);
>                 if (poolEntry.sessionFuture != null && 
> poolEntry.sessionFuture.isDone()) {
>                     poolEntry.sessionFuture = null;
>                 } {code}
> When poolEntry.sessionFuture.isDone() is true, the connection is already 
> ready, but the existing logic will abandon it and create a new one, and under 
> high load, this logic could create a lot of conns per endpoint, which 
> consumes a lot of memory.
>  
> The proposed fix:
> {code:java}
> if (poolEntry.session != null) {
>                 callback.completed(poolEntry.session);
>             } else {
>                 poolEntry.requestQueue.add(callback);
>                 if (poolEntry.sessionFuture != null && 
> poolEntry.sessionFuture.isDone()) {
>                     // Check whether we should recreate a new conn or not
>                     try {
>                         poolEntry.session = poolEntry.sessionFuture.get();
>                         while (true) {
>                             final FutureCallback<IOSession> pendingCallback = 
> poolEntry.requestQueue.poll();
>                             if (pendingCallback != null) {
>                                 pendingCallback.completed(poolEntry.session);
>                             } else {
>                                 break;
>                             }
>                         }
>                     } catch (final Exception e) {
>                         poolEntry.sessionFuture = null;
>                     }
>                 } {code}
> I am planning to cut a PR for this.
>  



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