Index: lucene/src/java/org/apache/lucene/index/IndexWriterConfig.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexWriterConfig.java	(revision 1206426)
+++ lucene/src/java/org/apache/lucene/index/IndexWriterConfig.java	(working copy)
@@ -695,6 +695,10 @@
    * to this.
    */
   public IndexWriterConfig setInfoStream(InfoStream infoStream) {
+    if (infoStream == null) {
+      throw new IllegalArgumentException("Cannot set InfoStream implementation to null. "+
+        "To disable logging use InfoStream.NO_OUTPUT");
+    }
     this.infoStream = infoStream;
     return this;
   }
@@ -703,8 +707,7 @@
    * Convenience method that uses {@link PrintStreamInfoStream}
    */
   public IndexWriterConfig setInfoStream(PrintStream printStream) {
-    this.infoStream = printStream == null ? null : new PrintStreamInfoStream(printStream);
-    return this;
+    return setInfoStream(printStream == null ? InfoStream.NO_OUTPUT : new PrintStreamInfoStream(printStream));
   }
 
   @Override
@@ -725,7 +728,7 @@
     sb.append("maxBufferedDocs=").append(maxBufferedDocs).append("\n");
     sb.append("mergedSegmentWarmer=").append(mergedSegmentWarmer).append("\n");
     sb.append("codec=").append(codec).append("\n");
-    sb.append("infoStream=").append(infoStream == null ? "null" : infoStream.getClass().getName()).append("\n");
+    sb.append("infoStream=").append(infoStream.getClass().getName()).append("\n");
     sb.append("mergePolicy=").append(mergePolicy).append("\n");
     sb.append("indexerThreadPool=").append(indexerThreadPool).append("\n");
     sb.append("readerPooling=").append(readerPooling).append("\n");
Index: lucene/src/java/org/apache/lucene/util/InfoStream.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/InfoStream.java	(revision 1206426)
+++ lucene/src/java/org/apache/lucene/util/InfoStream.java	(working copy)
@@ -26,22 +26,43 @@
   private static final AtomicInteger MESSAGE_ID = new AtomicInteger();
   protected final int messageID = MESSAGE_ID.getAndIncrement();
   
+  /** Instance of InfoStream that does no logging at all. */
+  public static final InfoStream NO_OUTPUT = new NoOutput();
+  private static final class NoOutput extends InfoStream {
+    @Override
+    public void message(String component, String message) {}
+    
+    @Override
+    public boolean isEnabled(String component) { return false; }
+
+    @Override
+    public void close() {}
+  }
+  
   /** prints a message */
   public abstract void message(String component, String message);
   
-  private static InfoStream defaultInfoStream;
+  /** returns true if messages are enabled and should be posted to {@link #message}. */
+  public abstract boolean isEnabled(String component);
   
-  /** The default infoStream (possibly null) used
-   * by a newly instantiated classes.
+  private static InfoStream defaultInfoStream = NO_OUTPUT;
+  
+  /** The default {@code InfoStream} used by a newly instantiated classes.
    * @see #setDefault */
-  public static InfoStream getDefault() {
+  public static synchronized InfoStream getDefault() {
     return defaultInfoStream;
   }
   
-  /** Sets the default infoStream (possibly null) used
-   * by a newly instantiated classes.
-   * @see #setDefault */
-  public static void setDefault(InfoStream infoStream) {
+  /** Sets the default {@code InfoStream} used
+   * by a newly instantiated classes. It cannot be {@code null},
+   * to disable logging use {@link #NO_OUTPUT}.
+   * @see #getDefault */
+  public static synchronized void setDefault(InfoStream infoStream) {
+    if (infoStream == null) {
+      throw new IllegalArgumentException("Cannot set InfoStream default implementation to null. "+
+        "To disable logging use InfoStream.NO_OUTPUT");
+    }
     defaultInfoStream = infoStream;
   }
+  
 }
Index: lucene/src/java/org/apache/lucene/util/PrintStreamInfoStream.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/PrintStreamInfoStream.java	(revision 1206426)
+++ lucene/src/java/org/apache/lucene/util/PrintStreamInfoStream.java	(working copy)
@@ -37,6 +37,11 @@
   }
 
   @Override
+  public boolean isEnabled(String component) {
+    return true;
+  }
+
+  @Override
   public void close() throws IOException {
     if (!isSystemStream()) {
       stream.close();
Index: lucene/src/test-framework/java/org/apache/lucene/util/FailOnNonBulkMergesInfoStream.java
===================================================================
--- lucene/src/test-framework/java/org/apache/lucene/util/FailOnNonBulkMergesInfoStream.java	(revision 1206426)
+++ lucene/src/test-framework/java/org/apache/lucene/util/FailOnNonBulkMergesInfoStream.java	(working copy)
@@ -26,6 +26,11 @@
   @Override
   public void close() throws IOException {   
   }
+  
+  @Override
+  public boolean isEnabled(String component) {
+    return true;
+  }
 
   @Override
   public void message(String component, String message) {
Index: lucene/src/test-framework/java/org/apache/lucene/util/NullInfoStream.java
===================================================================
--- lucene/src/test-framework/java/org/apache/lucene/util/NullInfoStream.java	(revision 1206426)
+++ lucene/src/test-framework/java/org/apache/lucene/util/NullInfoStream.java	(working copy)
@@ -20,7 +20,7 @@
 import java.io.IOException;
 
 /**
- * Prints nothing. Just to make sure tests pass w/ and without infostream
+ * Prints nothing. Just to make sure tests pass w/ and without enabled InfoStream
  * without actually making noise.
  * @lucene.experimental
  */
@@ -32,6 +32,11 @@
   }
   
   @Override
+  public boolean isEnabled(String component) {
+    return true; // to actually enable logging, we just ignore on message()
+  }
+
+  @Override
   public void close() throws IOException {   
   }
 }
Index: lucene/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java	(revision 1206426)
+++ lucene/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java	(working copy)
@@ -24,6 +24,7 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Random;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apache.lucene.analysis.*;
 import org.apache.lucene.document.Document;
@@ -960,19 +961,23 @@
   // LUCENE-1429
   public void testOutOfMemoryErrorCausesCloseToFail() throws Exception {
 
-    final List<Throwable> thrown = new ArrayList<Throwable>();
+    final AtomicBoolean thrown = new AtomicBoolean(false);
     final Directory dir = newDirectory();
     final IndexWriter writer = new IndexWriter(dir,
         newIndexWriterConfig( TEST_VERSION_CURRENT, new MockAnalyzer(random)).setInfoStream(new InfoStream() {
         @Override
         public void message(String component, final String message) {
-          if (message.startsWith("now flush at close") && 0 == thrown.size()) {
-            thrown.add(null);
+          if (message.startsWith("now flush at close") && thrown.compareAndSet(false, true)) {
             throw new OutOfMemoryError("fake OOME at " + message);
           }
         }
 
         @Override
+        public boolean isEnabled(String component) {
+          return true;
+        }
+        
+        @Override
         public void close() throws IOException {}
       }));