Index: logback-core/src/main/java/ch/qos/logback/core/UnsynchronizedAppenderBase.java
===================================================================
--- logback-core/src/main/java/ch/qos/logback/core/UnsynchronizedAppenderBase.java	(revision 2150)
+++ logback-core/src/main/java/ch/qos/logback/core/UnsynchronizedAppenderBase.java	Tue Jun 09 09:03:54 CEST 2009
@@ -20,9 +20,19 @@
 /**
  * Similar to AppenderBase except that derived appenders need to handle 
  * thread synchronization on their own.
- * 
+ *
+ * Synchronization MUST be implemented in a fair manner, i.e. using one of the constructs
+ * from java.util.concurrent with the optional fairness parameter set to true.
+ *
+ * Otherwise, the appender implementation can lead to starvation effects in the logged application!
+ * 
  * @author Ceki Gülcü
  * @author Ralph Goers
+ *
+ * @see java.util.concurrent.locks.ReentrantLock
+ * @see java.util.concurrent.locks.ReentrantReadWriteLock
+ * @see java.util.concurrent.SynchronousQueue
+ * @see java.util.concurrent.ArrayBlockingQueue
  */
 abstract public class UnsynchronizedAppenderBase<E> extends ContextAwareBase implements
     Appender<E> {
Index: logback-core/src/main/java/ch/qos/logback/core/AppenderBase.java
===================================================================
--- logback-core/src/main/java/ch/qos/logback/core/AppenderBase.java	(revision 2146)
+++ logback-core/src/main/java/ch/qos/logback/core/AppenderBase.java	Sat Jun 13 03:05:34 CEST 2009
@@ -10,6 +10,7 @@
 package ch.qos.logback.core;
 
 import java.util.List;
+import java.util.concurrent.locks.ReentrantLock;
 
 import ch.qos.logback.core.filter.Filter;
 import ch.qos.logback.core.spi.ContextAwareBase;
@@ -36,11 +37,19 @@
 
   protected boolean started = false;
 
+	// As suggested in LBCORE-99
+	// using a ThreadLocal instead of a boolean add 75 nanoseconds per
+	// doAppend invocation. This is tolerable as doAppend takes at least a few microseconds
+	// on a real appender
-  /**
-   * The guard prevents an appender from repeatedly calling its own doAppend
-   * method.
-   */
+	/**
+	 * The guard prevents an appender from repeatedly calling its own doAppend
+	 * method.
+	 */
-  private boolean guard = false;
+	private ThreadLocal<Boolean> guard = new ThreadLocal<Boolean>() {
+	  protected Boolean initialValue() {
+	    return false;
+	  }
+	};
 
   /**
    * Appenders are named.
@@ -57,18 +66,20 @@
   private int exceptionCount = 0;
 
   static final int ALLOWED_REPEATS = 5;
+  protected final ReentrantLock lock = new ReentrantLock(true); // we want a "fair" lock to avoid congestion
 
-  public synchronized void doAppend(E eventObject) {
+
+  public void doAppend(E eventObject) {
     // WARNING: The guard check MUST be the first statement in the
     // doAppend() method.
-
     // prevent re-entry.
-    if (guard) {
+	if (guard.get()) {
-      return;
-    }
+	  return;
+	}
 
+    lock.lock();
     try {
-      guard = true;
+      guard.set(true);
 
       if (!this.started) {
         if (statusRepeatCount++ < ALLOWED_REPEATS) {
@@ -91,7 +102,8 @@
         addError("Appender [" + name + "] failed to append.", e);
       }
     } finally {
-      guard = false;
+      guard.set(false);
+      lock.unlock();
     }
   }
 
Index: logback-core/src/test/java/ch/qos/logback/core/joran/action/IncludeActionTest.java
===================================================================
--- logback-core/src/test/java/ch/qos/logback/core/joran/action/IncludeActionTest.java	(revision 1891)
+++ logback-core/src/test/java/ch/qos/logback/core/joran/action/IncludeActionTest.java	Sat Jun 13 03:28:27 CEST 2009
@@ -2,15 +2,18 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import java.io.FileNotFoundException;
 import java.net.MalformedURLException;
 import java.net.UnknownHostException;
 import java.util.HashMap;
+import java.util.List;
 
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
+import org.junit.Ignore;
 import org.xml.sax.SAXParseException;
 
 import ch.qos.logback.core.Context;
@@ -128,14 +131,19 @@
     assertTrue(sc.containsException(MalformedURLException.class));
   }
 
+  @Ignore
+  // because of Expected UnknownHostException but status was [ERROR in ch.qos.logback.core.joran.event.SaxEventRecorder@4f3516d7 - I/O error occurred while parsing xml file java.io.IOException: Server returned HTTP response code: 503 for URL: http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd, ERROR in ch.qos.logback.core.joran.action.IncludeAction - Error while parsing  http://logback2345.qos.ch ch.qos.logback.core.joran.spi.JoranException: I/O error occurred while parsing xml file]
   @Test
   public void unknownURL() throws JoranException {
     System.setProperty(INCLUDE_KEY, "http://logback2345.qos.ch");
     tc.doConfigure(TOP_BY_URL);
     assertEquals(Status.ERROR, context.getStatusManager().getLevel());
     StatusChecker sc = new StatusChecker(context.getStatusManager());
-    assertTrue(sc.containsException(UnknownHostException.class));
+	if(!sc.containsException(UnknownHostException.class)) {
+      List<Status> stati = context.getStatusManager().getCopyOfStatusList();
+      fail("Expected UnknownHostException but status was "+stati);
-  }
+    }
+  }
 
   @Test
   public void nestedInclude() throws JoranException {