Index: src/java/org/apache/lucene/store/MMapDirectory.java
===================================================================
--- src/java/org/apache/lucene/store/MMapDirectory.java	(revision 988223)
+++ src/java/org/apache/lucene/store/MMapDirectory.java	(working copy)
@@ -68,6 +68,13 @@
  * an undocumented internal cleanup functionality.
  * {@link #UNMAP_SUPPORTED} is <code>true</code>, if the workaround
  * can be enabled (with no guarantees).
+ * <p>
+ * <b>NOTE:</b> Accessing this class either directly or
+ * indirectly from a thread while it's interrupted can close the
+ * underlying channel immediately if at the same time the thread is
+ * blocked on IO. The channel will remain closed and subsequent access
+ * to {@link MMapDirectory} will throw a {@link ClosedChannelException}. 
+ * </p>
  */
 public class MMapDirectory extends FSDirectory {
   private boolean useUnmapHack = false;
Index: src/java/org/apache/lucene/store/NIOFSDirectory.java
===================================================================
--- src/java/org/apache/lucene/store/NIOFSDirectory.java	(revision 988223)
+++ src/java/org/apache/lucene/store/NIOFSDirectory.java	(working copy)
@@ -21,22 +21,32 @@
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
+import java.util.concurrent.Future; // javadoc
 
 /**
- * An {@link FSDirectory} implementation that uses
- * java.nio's FileChannel's positional read, which allows
- * multiple threads to read from the same file without
- * synchronizing.
- *
- * <p>This class only uses FileChannel when reading; writing
- * is achieved with {@link FSDirectory.FSIndexOutput}.
- * 
- * <p><b>NOTE</b>: NIOFSDirectory is not recommended on Windows because of a bug
- * in how FileChannel.read is implemented in Sun's JRE.
- * Inside of the implementation the position is apparently
- * synchronized.  See <a
+ * An {@link FSDirectory} implementation that uses java.nio's FileChannel's
+ * positional read, which allows multiple threads to read from the same file
+ * without synchronizing.
+ * <p>
+ * This class only uses FileChannel when reading; writing is achieved with
+ * {@link SimpleFSDirectory.SimpleFSIndexOutput}.
+ * <p>
+ * <b>NOTE</b>: NIOFSDirectory is not recommended on Windows because of a bug in
+ * how FileChannel.read is implemented in Sun's JRE. Inside of the
+ * implementation the position is apparently synchronized. See <a
  * href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6265734">here</a>
  * for details.
+ * </p>
+ * <p>
+ * <font color="red"><b>NOTE:</b> Accessing this class either directly or
+ * indirectly from a thread while it's interrupted can close the
+ * underlying file descriptor immediately if at the same time the thread is
+ * blocked on IO. The file descriptor will remain closed and subsequent access
+ * to {@link NIOFSDirectory} will throw a {@link ClosedChannelException}. If
+ * your application uses either {@link Thread#interrupt()} or
+ * {@link Future#cancel(boolean)} you should use {@link SimpleFSDirectory} in
+ * favor of {@link NIOFSDirectory}.</font>
+ * </p>
  */
 public class NIOFSDirectory extends FSDirectory {