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diff --git a/src/mongo/util/intrusive_counter.h b/src/mongo/util/intrusive_counter.h
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+/**
+ * Copyright (c) 2011 10gen Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <boost/intrusive_ptr.hpp>
+#include <boost/noncopyable.hpp>
+
+namespace mongo {
+
+/*
+  IntrusiveCounter is a sharable implementation of a reference counter that
+  objects can use to be compatible with boost::intrusive_ptr<>.
+
+  Some objects that use IntrusiveCounter are immutable, and only have
+  const methods.  This may require their pointers to be declared as
+  intrusive_ptr<const ClassName> .  In order to be able to share pointers to
+  these immutables, the methods associated with IntrusiveCounter are declared
+  as const, and the counter itself is marked as mutable.
+
+  IntrusiveCounter itself is abstract, allowing for multiple implementations.
+  For example, IntrusiveCounterUnsigned uses ordinary unsigned integers for
+  the reference count, and is good for situations where thread safety is not
+  required.  For others, other implementations using atomic integers should
+  be used.  For static objects, the implementations of addRef() and release()
+  can be overridden to do nothing.
+ */
+    class IntrusiveCounter :
+        boost::noncopyable {
+    public:
+	virtual ~IntrusiveCounter() {};
+
+	// these are here for the boost intrusive_ptr<> class
+	friend inline void intrusive_ptr_add_ref(const IntrusiveCounter *pIC) {
+	    pIC->addRef(); };
+	friend inline void intrusive_ptr_release(const IntrusiveCounter *pIC) {
+	    pIC->release(); };
+
+	virtual void addRef() const = 0;
+	virtual void release() const = 0;
+    };
+
+    class IntrusiveCounterUnsigned :
+        public IntrusiveCounter {
+    public:
+	// virtuals from IntrusiveCounter
+	virtual void addRef() const;
+	virtual void release() const;
+
+	IntrusiveCounterUnsigned();
+
+    private:
+	mutable unsigned counter;
+    };
+
+};
+
+/* ======================= INLINED IMPLEMENTATIONS ========================== */
+
+namespace mongo {
+
+    inline IntrusiveCounterUnsigned::IntrusiveCounterUnsigned():
+	counter(0) {
+    }
+
+};