[jboss-jira] [JBoss JIRA] Commented: (JGRP-1085) NakReceiverWindow: possibly replace ReadWriteLock

[Bela Ban (JIRA)]

    [ https://jira.jboss.org/jira/browse/JGRP-1085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12492424#action_12492424 ] 

Bela Ban commented on JGRP-1085:
--------------------------------

For example, in NakReceiverWindow.add(), we can de-scope it like this:

void add(seqno, msg) {

   lock:

       if(seqno == current): action=PUT
       if(seqno < current): return
       if(seqno > current): action=PUT_AND_XMIT
       else action=PUT_IF_ABSENT
   end-lock:

   switch(action):
        case PUT: xmit_table.put(seqno, msg)
        case PUT_AND_XMIT: xmit_table.put(seqn,msg) / retransmitter.put(seqno)
        case PUT_IF_ABSENT: if xmit_table.putIfAbsent(seqn, msg) --> retransmitter.remove(seqno)
}

The work inside the lock scope is only to determine what to do with the message, the real (and costly) work is done *outside* the scope, so we can have more concurrent add() invocations. 

Same for NakReceiverWindow.removeMany():
- Determine in the lock scope how many messages we can remove (add them to a list and add the seqnos of messages to be discarded from the xmit_table to a different list.
- After the lock-scope: remove all seqnos from xmit_table (if any) and return list

TODO: write a test which only uses NakReceiverWindow and measures how long it takes to insert 1 million messages. With the changes above, this should be faster !

> NakReceiverWindow: possibly replace ReadWriteLock
> -------------------------------------------------
>
>                 Key: JGRP-1085
>                 URL: https://jira.jboss.org/jira/browse/JGRP-1085
>             Project: JGroups
>          Issue Type: Task
>            Reporter: Bela Ban
>            Priority: Minor
>             Fix For: 2.9
>
>
> Take a look at performance of RW locks, [1] suggests it is bad and writer threads get starved by many reader threads.
> [1] http://www.javaspecialists.eu/archive/Issue165.html

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