/*
 * Created on Jul 28, 2004
 * Created by Alon Rohter
 * Copyright (C) Azureus Software, Inc, All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 */
package com.aelitis.azureus.core.networkmanager.impl.tcp;

import org.gudy.azureus2.core3.logging.*;
import org.gudy.azureus2.core3.util.*;


/**
 * Temp class designed to help detect Selector anomalies and cleanly re-open if necessary.
 * 
 * NOTE:
 * As of JVM 1.4.2_03, after network connection disconnect/reconnect, usually-blocking
 * select() and select(long) calls no longer block, and will instead return immediately.
 * This can cause selector spinning and 100% cpu usage.
 * See:
 *   http://forum.java.sun.com/thread.jsp?forum=4&thread=293213
 *   http://developer.java.sun.com/developer/bugParade/bugs/4850373.html
 *   http://developer.java.sun.com/developer/bugParade/bugs/4881228.html
 * Fixed in JVM 1.4.2_05+ and 1.5b2+
 */
public class SelectorGuard {
  private static final int SELECTOR_SPIN_THRESHOLD    = 200;
  private static final int SELECTOR_FAILURE_THRESHOLD = 10000;
  private static final int MAX_IGNORES = 5;
  
  private boolean marked = false;
  private int consecutiveZeroSelects = 0;
  private long beforeSelectTime;
  private long select_op_time;

  private final String type;
  private final GuardListener listener;
  private int ignores = 0;

  
  /**
   * Create a new SelectorGuard with the given failed count threshold.
   */
  public SelectorGuard( String _type, GuardListener _listener ) {
    this.type = _type;
    this.listener = _listener;
  }
  
  public String
  getType()
  {
	  return( type );
  }
  
  /**
   * Run this method right before the select() operation to
   * mark the start time.
   */
  public void markPreSelectTime() {
    beforeSelectTime = SystemTime.getCurrentTime();
    marked = true;
  }
  
  
  /**
   * Checks whether selector is still OK, and not spinning.
   */
  public void verifySelectorIntegrity( int num_keys_ready, long time_threshold ) {    
    if( num_keys_ready > 0 ) {  //non-zero select, so OK
      ignores++;      
      if( ignores > MAX_IGNORES ) {  //allow MAX_IGNORES / SELECTOR_SPIN_THRESHOLD to be successful select ops and still trigger a spin alert
        ignores = 0;
        consecutiveZeroSelects = 0;
      }
      return;
    }
    
    if (marked) marked = false;
    else Debug.out("Error: You must run markPreSelectTime() before calling isSelectorOK");
    
    select_op_time = SystemTime.getCurrentTime() - beforeSelectTime;
    
    if( select_op_time > time_threshold || select_op_time < 0 ) {
      //zero-select, but over the time threshold, so OK
      consecutiveZeroSelects = 0;
      return;
    }
    
    //if we've gotten here, then we have a potential selector anomalie
    consecutiveZeroSelects++;
    
    if( consecutiveZeroSelects % 20 == 0 && Constants.isWindows ) {
    	// getting triggered with 20 +_ sometimes 40 due to general high CPU usage
      if ( consecutiveZeroSelects > 40 ){
    	  Debug.out( "consecutiveZeroSelects=" +consecutiveZeroSelects );
      }
    }
    
    
    if( consecutiveZeroSelects > SELECTOR_SPIN_THRESHOLD ) {
      if( Constants.isWindows && (Constants.JAVA_VERSION.startsWith("1.4") || Constants.JAVA_VERSION.startsWith("1.5"))) {
        //Under windows, it seems that selector spin can sometimes appear when >63 socket channels are registered with a selector
    	//Should be fixed in later 1.5, but play it safe and assume 1.6 or newer only.
        if( !listener.safeModeSelectEnabled() ) {
          String msg = "Likely faulty socket selector detected: reverting to safe-mode socket selection. [JRE " +Constants.JAVA_VERSION+"]\n";
          msg += "Please see " +Constants.AZUREUS_WIKI+ "LikelyFaultySocketSelector for help.";
          Debug.out( msg );
          Logger.log(new LogAlert(LogAlert.UNREPEATABLE, LogAlert.AT_WARNING, msg));
        
          consecutiveZeroSelects = 0;
          listener.spinDetected();
          return;
        }
      }
      else {
        //under linux, it seems that selector spin is somewhat common, but normal??? behavior, so just sleep a bit
        consecutiveZeroSelects = 0;
        try{  Thread.sleep( 50 );  }catch( Throwable t) {t.printStackTrace();}
        return;
      }
    }
    
    
    if( consecutiveZeroSelects > SELECTOR_FAILURE_THRESHOLD ) {  //should only happen under Windows + JRE 1.4
      String msg = "Likely network disconnect/reconnect: Repairing socket channel selector. [JRE " +Constants.JAVA_VERSION+"]\n";
      msg += "Please see " +Constants.AZUREUS_WIKI+ "LikelyNetworkDisconnectReconnect for help.";
      Debug.out( msg );
      Logger.log(new LogAlert(LogAlert.UNREPEATABLE, LogAlert.AT_WARNING, msg));
      
      consecutiveZeroSelects = 0;
      listener.failureDetected();
      return;
    }
    
    //not yet over the count threshold
  }
  

  
  public interface GuardListener {
    public boolean safeModeSelectEnabled();
    public void spinDetected();
    public void failureDetected();
  }
  
}
