Index: logback-core/src/main/java/ch/qos/logback/core/AppenderBase.java
===================================================================
--- logback-core/src/main/java/ch/qos/logback/core/AppenderBase.java	(revision 2265)
+++ logback-core/src/main/java/ch/qos/logback/core/AppenderBase.java	Tue May 19 17:06:49 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;
@@ -57,11 +58,15 @@
   private int exceptionCount = 0;
 
   static final int ALLOWED_REPEATS = 5;
+  private 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) {
+    lock.lock();
+
+    try {
     // WARNING: The guard check MUST be the first statement in the
     // doAppend() method.
-
     // prevent re-entry.
     if (guard) {
       return;
@@ -93,7 +98,10 @@
     } finally {
       guard = false;
     }
+    } finally {
+      lock.unlock();
-  }
+    }
+  }
 
   abstract protected void append(E eventObject);