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diff --git a/antlr-3.4/tool/src/main/java/org/antlr/misc/Barrier.java b/antlr-3.4/tool/src/main/java/org/antlr/misc/Barrier.java
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+/*
+ * [The "BSD license"]
+ *  Copyright (c) 2010 Terence Parr
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions
+ *  are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in the
+ *      documentation and/or other materials provided with the distribution.
+ *  3. The name of the author may not be used to endorse or promote products
+ *      derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.antlr.misc;
+
+/**A very simple barrier wait.  Once a thread has requested a
+ * wait on the barrier with waitForRelease, it cannot fool the
+ * barrier into releasing by "hitting" the barrier multiple times--
+ * the thread is blocked on the wait().
+ */
+public class Barrier {
+    protected int threshold;
+    protected int count = 0;
+
+    public Barrier(int t) {
+        threshold = t;
+    }
+
+    public synchronized void waitForRelease()
+        throws InterruptedException
+    {
+        count++;
+        // The final thread to reach barrier resets barrier and
+        // releases all threads
+        if ( count==threshold ) {
+            // notify blocked threads that threshold has been reached
+            action(); // perform the requested operation
+            notifyAll();
+        }
+        else while ( count<threshold ) {
+            wait();
+        }
+    }
+
+    /** What to do when everyone reaches barrier */
+    public void action() {
+    }
+}