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https://issues.apache.org/jira/browse/ZOOKEEPER-59?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12840735#action_12840735
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Benjamin Reed commented on ZOOKEEPER-59:
----------------------------------------

i like how you removed the nested locking, but it looks like you missed an 
opportunity in the last block. don't you really want to 

{noformat}
synchronized(this) {outstandingRequests--;}
{noformat}

so that you aren't locking this and this.factory?

> Synchronized block in NIOServerCnxn
> -----------------------------------
>
>                 Key: ZOOKEEPER-59
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-59
>             Project: Zookeeper
>          Issue Type: Bug
>          Components: server
>            Reporter: Flavio Paiva Junqueira
>            Assignee: Flavio Paiva Junqueira
>             Fix For: 3.3.0
>
>         Attachments: ZOOKEEPER-59.patch, ZOOKEEPER-59.patch
>
>
> There are two synchronized blocks locking on different objects, and to me 
> they should be guarded by the same object. Here are the parts of the code I'm 
> talking about:
> {noformat}
> nioservercnxn.readrequ...@444
> ...
>           synchronized (this) {
>                 outstandingRequests++;
>                 // check throttling
>                 if (zk.getInProcess() > factory.outstandingLimit) {
>                     disableRecv();
>                     // following lines should not be needed since we are 
> already
>                     // reading
>                     // } else {
>                     // enableRecv();
>                 }
>             } 
> {noformat}
> {noformat}
> nioservercnxn.sendrespo...@740
> ...
>          synchronized (this.factory) {
>                 outstandingRequests--;
>                 // check throttling
>                 if (zk.getInProcess() < factory.outstandingLimit
>                         || outstandingRequests < 1) {
>                     sk.selector().wakeup();
>                     enableRecv();
>                 }
>             }
> {noformat}
> I think the second one is correct, and the first synchronized block should be 
> guarded by "this.factory". 
> This could be related to issue ZOOKEEPER-57, but I have no concrete 
> indication that this is the case so far.

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