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SelectorGuard.javaAPI DocAzureus 3.0.3.45818Thu Aug 30 00:27:54 BST 2007com.aelitis.azureus.core.networkmanager.impl.tcp

SelectorGuard

public class SelectorGuard extends Object
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+

Fields Summary
private static final int
SELECTOR_SPIN_THRESHOLD
private static final int
SELECTOR_FAILURE_THRESHOLD
private static final int
MAX_IGNORES
private boolean
marked
private int
consecutiveZeroSelects
private long
beforeSelectTime
private long
select_op_time
private final String
type
private final GuardListener
listener
private int
ignores
Constructors Summary
public SelectorGuard(String _type, GuardListener _listener)
Create a new SelectorGuard with the given failed count threshold.


  
               
         
    this.type = _type;
    this.listener = _listener;
Methods Summary
public java.lang.StringgetType()

	  return( type );
public voidmarkPreSelectTime()
Run this method right before the select() operation to mark the start time.

    beforeSelectTime = SystemTime.getCurrentTime();
    marked = true;
public voidverifySelectorIntegrity(int num_keys_ready, long time_threshold)
Checks whether selector is still OK, and not spinning.

    
    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