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  /*
   ***** BEGIN LICENSE BLOCK *****
   * Version: EPL 1.0/GPL 2.0/LGPL 2.1
   *
   * The contents of this file are subject to the Eclipse Public
   * License Version 1.0 (the "License"); you may not use this file
   * except in compliance with the License. You may obtain a copy of
   * the License at http://www.eclipse.org/legal/epl-v10.html
   *
  * Software distributed under the License is distributed on an "AS
  * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
  * implied. See the License for the specific language governing
  * rights and limitations under the License.
  *
  * Copyright (C) 2010 Charles O Nutter <headius@headius.com>
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either of the GNU General Public License Version 2 or later (the "GPL"),
  * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  * in which case the provisions of the GPL or the LGPL are applicable instead
  * of those above. If you wish to allow use of your version of this file only
  * under the terms of either the GPL or the LGPL, and not to allow others to
  * use your version of this file under the terms of the EPL, indicate your
  * decision by deleting the provisions above and replace them with the notice
  * and other provisions required by the GPL or the LGPL. If you do not delete
  * the provisions above, a recipient may use your version of this file under
  * the terms of any one of the EPL, the GPL or the LGPL.
  ***** END LICENSE BLOCK *****/
 
 package org.jruby.util.io;
 
 import java.util.List;
 
 import java.util.Map;

This is a simple implementation of a hard-referenced java.nio.channels.Selector pool. It is intended to allow us to reuse a small pool of selectors rather than creating them new for each use (which causes problem for Windows and its socket-per-selector impl) or saving them per-thread (which causes problems when there are many not-quite-dead threads in flight. The selectors are kept open in the pool and you should call cleanup() for releasing selectors.

Author(s):
headius
 
 public class SelectorPool {
     private final Map<SelectorProviderList<Selector>> pool = new HashMap<SelectorProviderList<Selector>>();

    
Get a selector from the pool (or create a new one). Selectors come from the default selector provider on the current JVM.

Returns:
a java.nio.channels.Selector
Throws:
java.io.IOException if there's a problem opening a new selector
 
     public synchronized Selector get() throws IOException{
         return retrieveFromPool(SelectorProvider.provider());
     }

    
Get a selector from the pool (or create a new one). Selectors come from the given provider.

Returns:
a java.nio.channels.Selector
Throws:
java.io.IOException if there's a problem opening a new selector
 
     public synchronized Selector get(SelectorProvider providerthrows IOException{
         return retrieveFromPool(provider);
     }

    
Put a selector back into the pool.

Parameters:
selector the selector to put back
 
     public synchronized void put(Selector selector) {
         returnToPool(selector);
     }
    
    
Clean up a pool. All selectors in a pool are closed and the pool gets empty.
 
     public synchronized void cleanup() {
         for (Map.Entry<SelectorProviderList<Selector>> entry : .entrySet()) {
             List<SelectorproviderPool = entry.getValue();
             while (!providerPool.isEmpty()) {
                 Selector selector = providerPool.remove(providerPool.size() - 1);
                 try {
                     selector.close();
                } catch (IOException ioe) {
                    // ignore IOException at termination.
                }
            }
        }
        .clear();
    }
    private Selector retrieveFromPool(SelectorProvider providerthrows IOException {
        List<SelectorproviderPool = .get(provider);
        if (providerPool != null && !providerPool.isEmpty()) {
            return providerPool.remove(providerPool.size() - 1);
        }
        return SelectorFactory.openWithRetryFrom(nullprovider);
    }
    private void returnToPool(Selector selector) {
        SelectorProvider provider = selector.provider();
        List<SelectorproviderPool = .get(provider);
        if (providerPool == null) {
            providerPool = new LinkedList<Selector>();
            .put(providerproviderPool);
        }
        providerPool.add(selector);
    }
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