Jetty: insufficient threads configured for SelectChannelConnector

The Problem
Today when I run our Solr application in one machine, during start, it reports warning:
Oct 6, 2014 7:25:15 PM org.eclipse.jetty.server.AbstractConnector doStart
WARNING: insufficient threads configured for SelectChannelConnector@0.0.0.0:12345

Trying http request in browser, no response, just hang forever.

Inspect the solr server in Visual VM. In threads tab, it shows there is 238 live threads, and a lot of selector(128) and acceptors(72). This looks very suspiciours:
qtp1287645725-145 Selector127
   java.lang.Thread.State: BLOCKED
   java.lang.Thread.State: RUNNABLE at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method) at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:273) at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:255) at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:136) at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:69) - locked (a sun.nio.ch.Util$2)

"qtp1287645725-217 Acceptor71 SelectChannelConnector@0.0.0.0:12345"
   java.lang.Thread.State: BLOCKED
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:134)
- waiting to lock (a java.lang.Object) owned by "qtp1287645725-221 Acceptor71 SelectChannelConnector@0.0.0.0:12345" t@221
at org.eclipse.jetty.server.nio.SelectChannelConnector.accept(SelectChannelConnector.java:109)


Then check the code: When start jetty, the code sets acceptors to number of cpu cores * 2. in this machine,  There is 64 cores. This will cause jetty to start 64*2 = 128 selectors and acceptors. 
connector.setAcceptors(2 * Runtime.getRuntime().availableProcessors());

The default acceptors is:(Runtime.getRuntime().availableProcessors()+3)/4 which is 16 in this case. 
setAcceptors(Math.max(1,(Runtime.getRuntime().availableProcessors()+3)/4));

So to fix this issue,  I just comment or cusom acceptors code: connector.setAcceptors(2 * Runtime.getRuntime().availableProcessors()); 

Lesson Learned
Be careful when tune server performance, make sure you truly understand its meaning.

Configure ThreadPool in jetty.xml

<Set name="ThreadPool">
  <New class="org.eclipse.jetty.util.thread.QueuedThreadPool">
    <Set name="minThreads">10</Set>
    <Set name="maxThreads">200</Set>
    <Set name="detailedDump">false</Set>
  </New>
</Set>

Jetty Code:
During startup, jetty will start acceptors(2=128 in this case) selectors:
org.eclipse.jetty.server.nio.SelectChannelConnector.doStart()
protected void doStart() throws Exception
{
    _manager.setSelectSets(getAcceptors());
    super.doStart();
}
org.eclipse.jetty.io.nio.SelectorManager.doStart()
protected void doStart() throws Exception
{
    _selectSet = new SelectSet[_selectSets];
    for (int i=0;i<_selectset .length="" i="" p="">        _selectSet[i]= new SelectSet(i);

    super.doStart();

    // start a thread to Select
    for (int i=0;i    {
        final int id=i;
        boolean selecting=dispatch(new Runnable()
        {
            public void run()
            {
            // ....
            }

        });
    }
}