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diff --git a/src/common/simple_cache.hpp b/src/common/simple_cache.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_SIMPLECACHE_H
+#define CEPH_SIMPLECACHE_H
+
+#include <list>
+#include <map>
+#include <unordered_map>
+#include <utility>
+
+#include "common/ceph_mutex.h"
+
+template <class K, class V, class C = std::less<K>, class H = std::hash<K> >
+class SimpleLRU {
+  ceph::mutex lock = ceph::make_mutex("SimpleLRU::lock");
+  size_t max_size;
+  size_t max_bytes = 0;
+  size_t total_bytes = 0;
+  std::unordered_map<K, typename std::list<std::pair<K, V>>::iterator, H> contents;
+  std::list<std::pair<K, V> > lru;
+  std::map<K, V, C> pinned;
+
+  void trim_cache() {
+    while (contents.size() > max_size) {
+      contents.erase(lru.back().first);
+      lru.pop_back();
+    }
+  }
+
+  void trim_cache_bytes() {
+    while(total_bytes > max_bytes) {
+      total_bytes -= lru.back().second.length();
+      contents.erase(lru.back().first);
+      lru.pop_back();
+    }
+  }
+
+  void _add(K key, V&& value) {
+    lru.emplace_front(key, std::move(value)); // can't move key because we access it below
+    contents[key] = lru.begin();
+    trim_cache();
+  }
+
+  void _add_bytes(K key, V&& value) {
+    lru.emplace_front(key, std::move(value)); // can't move key because we access it below
+    contents[key] = lru.begin();
+    trim_cache_bytes();
+  }
+
+public:
+  SimpleLRU(size_t max_size) : max_size(max_size) {
+    contents.rehash(max_size);
+  }
+
+  void pin(K key, V val) {
+    std::lock_guard l(lock);
+    pinned.emplace(std::move(key), std::move(val));
+  }
+
+  void clear_pinned(K e) {
+    std::lock_guard l(lock);
+    for (auto i = pinned.begin();
+	 i != pinned.end() && i->first <= e;
+	 pinned.erase(i++)) {
+      auto iter = contents.find(i->first);
+      if (iter == contents.end())
+	_add(i->first, std::move(i->second));
+      else
+	lru.splice(lru.begin(), lru, iter->second);
+    }
+  }
+
+  void clear(K key) {
+    std::lock_guard l(lock);
+    auto i = contents.find(key);
+    if (i == contents.end())
+      return;
+    total_bytes -= i->second->second.length();
+    lru.erase(i->second);
+    contents.erase(i);
+  }
+
+  void set_size(size_t new_size) {
+    std::lock_guard l(lock);
+    max_size = new_size;
+    trim_cache();
+  }
+
+  size_t get_size() {
+    std::lock_guard l(lock);
+    return contents.size();
+  }
+
+  void set_bytes(size_t num_bytes) {
+    std::lock_guard l(lock);
+    max_bytes = num_bytes;
+    trim_cache_bytes();
+  }
+
+  size_t get_bytes() {
+    std::lock_guard l(lock);
+    return total_bytes;
+  }
+
+  bool lookup(K key, V *out) {
+    std::lock_guard l(lock);
+    auto i = contents.find(key);
+    if (i != contents.end()) {
+      *out = i->second->second;
+      lru.splice(lru.begin(), lru, i->second);
+      return true;
+    }
+    auto i_pinned = pinned.find(key);
+    if (i_pinned != pinned.end()) {
+      *out = i_pinned->second;
+      return true;
+    }
+    return false;
+  }
+
+  void add(K key, V value) {
+    std::lock_guard l(lock);
+    _add(std::move(key), std::move(value));
+  }
+
+  void add_bytes(K key, V value) {
+    std::lock_guard l(lock);
+    total_bytes += value.length();
+    _add_bytes(std::move(key), std::move(value));
+  }
+};
+
+#endif