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diff --git a/src/common/sharedptr_registry.hpp b/src/common/sharedptr_registry.hpp
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+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+/*
+ * Ceph - scalable distributed file system
+ *
+ * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
+ *
+ * This is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License version 2.1, as published by the Free Software
+ * Foundation.  See file COPYING.
+ *
+ */
+
+#ifndef CEPH_SHAREDPTR_REGISTRY_H
+#define CEPH_SHAREDPTR_REGISTRY_H
+
+#include <map>
+#include <memory>
+#include "common/ceph_mutex.h"
+
+/**
+ * Provides a registry of shared_ptr<V> indexed by K while
+ * the references are alive.
+ */
+template <class K, class V, class C = std::less<K> >
+class SharedPtrRegistry {
+public:
+  typedef std::shared_ptr<V> VPtr;
+  typedef std::weak_ptr<V> WeakVPtr;
+  int waiting;
+private:
+  ceph::mutex lock = ceph::make_mutex("SharedPtrRegistry::lock");
+  ceph::condition_variable cond;
+  std::map<K, std::pair<WeakVPtr, V*>, C> contents;
+
+  class OnRemoval {
+    SharedPtrRegistry<K,V,C> *parent;
+    K key;
+  public:
+    OnRemoval(SharedPtrRegistry<K,V,C> *parent, K key) :
+      parent(parent), key(key) {}
+    void operator()(V *to_remove) {
+      {
+	std::lock_guard l(parent->lock);
+	typename std::map<K, std::pair<WeakVPtr, V*>, C>::iterator i =
+	  parent->contents.find(key);
+	if (i != parent->contents.end() &&
+	    i->second.second == to_remove) {
+	  parent->contents.erase(i);
+	  parent->cond.notify_all();
+	}
+      }
+      delete to_remove;
+    }
+  };
+  friend class OnRemoval;
+
+public:
+  SharedPtrRegistry() :
+    waiting(0)
+  {}
+
+  bool empty() {
+    std::lock_guard l(lock);
+    return contents.empty();
+  }
+
+  bool get_next(const K &key, std::pair<K, VPtr> *next) {
+    std::pair<K, VPtr> r;
+    {
+      std::lock_guard l(lock);
+      VPtr next_val;
+      typename std::map<K, std::pair<WeakVPtr, V*>, C>::iterator i =
+	contents.upper_bound(key);
+      while (i != contents.end() &&
+	     !(next_val = i->second.first.lock()))
+	++i;
+      if (i == contents.end())
+	return false;
+      if (next)
+	r = std::make_pair(i->first, next_val);
+    }
+    if (next)
+      *next = r;
+    return true;
+  }
+
+  
+  bool get_next(const K &key, std::pair<K, V> *next) {
+    VPtr next_val;
+    std::lock_guard l(lock);
+    typename std::map<K, std::pair<WeakVPtr, V*>, C>::iterator i =
+      contents.upper_bound(key);
+    while (i != contents.end() &&
+	   !(next_val = i->second.first.lock()))
+      ++i;
+    if (i == contents.end())
+      return false;
+    if (next)
+      *next = std::make_pair(i->first, *next_val);
+    return true;
+  }
+
+  VPtr lookup(const K &key) {
+    std::unique_lock l(lock);
+    waiting++;
+    while (1) {
+      typename std::map<K, std::pair<WeakVPtr, V*>, C>::iterator i =
+	contents.find(key);
+      if (i != contents.end()) {
+	VPtr retval = i->second.first.lock();
+	if (retval) {
+	  waiting--;
+	  return retval;
+	}
+      } else {
+	break;
+      }
+      cond.wait(l);
+    }
+    waiting--;
+    return VPtr();
+  }
+
+  VPtr lookup_or_create(const K &key) {
+    std::unique_lock l(lock);
+    waiting++;
+    while (1) {
+      typename std::map<K, std::pair<WeakVPtr, V*>, C>::iterator i =
+	contents.find(key);
+      if (i != contents.end()) {
+	VPtr retval = i->second.first.lock();
+	if (retval) {
+	  waiting--;
+	  return retval;
+	}
+      } else {
+	break;
+      }
+      cond.wait(l);
+    }
+    V *ptr = new V();
+    VPtr retval(ptr, OnRemoval(this, key));
+    contents.insert(std::make_pair(key, make_pair(retval, ptr)));
+    waiting--;
+    return retval;
+  }
+
+  unsigned size() {
+    std::lock_guard l(lock);
+    return contents.size();
+  }
+
+  void remove(const K &key) {
+    std::lock_guard l(lock);
+    contents.erase(key);
+    cond.notify_all();
+  }
+
+  template<class A>
+  VPtr lookup_or_create(const K &key, const A &arg) {
+    std::unique_lock l(lock);
+    waiting++;
+    while (1) {
+      typename std::map<K, std::pair<WeakVPtr, V*>, C>::iterator i =
+	contents.find(key);
+      if (i != contents.end()) {
+	VPtr retval = i->second.first.lock();
+	if (retval) {
+	  waiting--;
+	  return retval;
+	}
+      } else {
+	break;
+      }
+      cond.wait(l);
+    }
+    V *ptr = new V(arg);
+    VPtr retval(ptr, OnRemoval(this, key));
+    contents.insert(std::make_pair(key, make_pair(retval, ptr)));
+    waiting--;
+    return retval;
+  }
+
+  friend class SharedPtrRegistryTest;
+};
+
+#endif