initial code repo

[stor4nfv.git] / src / ceph / src / common / random_cache.hpp

diff --git a/src/ceph/src/common/random_cache.hpp b/src/ceph/src/common/random_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) 2014 UnitedStack <haomai@unitedstack.com>
+ *
+ * Author: Haomai Wang <haomaiwang@gmail.com>
+ *
+ * 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_RANDOMCACHE_H
+#define CEPH_RANDOMCACHE_H
+
+#include "common/Mutex.h"
+#include "include/compat.h"
+#include "include/unordered_map.h"
+
+
+// Although This is a ramdom cache implementation, here still consider to make
+// the trim progress more reasonable. Each item owns its lookup frequency,
+// when the cache is full it will randomly pick up several items and compare the
+// frequency associated with. The least frequency of items will be evicted.
+template <class K, class V>
+class RandomCache {
+  // The first element of pair is the frequency of item, it's used to evict item
+  ceph::unordered_map<K, pair<uint64_t, V> > contents;
+  Mutex lock;
+  uint64_t max_size;
+  K last_trim_key;
+
+  // When cache reach full, consider to evict a certain number of items
+  static const uint64_t EVICT_COUNT = 5;
+  // Avoid too much overhead on comparing items's frequency, the number of
+  // compare items is expected to small.
+  static const uint64_t COMPARE_COUNT = 3;
+
+  // In order to make evict cache progress more lightweight and effective,
+  // several items are expected to evicted in one call
+  void trim_cache(uint64_t evict_count) {
+    typename ceph::unordered_map<K, pair<uint64_t, V> >::iterator it = contents.find(last_trim_key);
+    uint64_t total_compare = evict_count * COMPARE_COUNT;
+    map<uint64_t, K> candidates;
+
+    while (total_compare--) {
+      if (it == contents.end()) {
+        it = contents.begin();
+      }
+
+      candidates[it->second.first] = it->first;
+      it++;
+    }
+    if (it != contents.end())
+      last_trim_key = it->first;
+    else
+      last_trim_key = contents.begin()->first;
+
+    for (typename map<uint64_t, K>::iterator j = candidates.begin(); j != candidates.end(); j++) {
+      contents.erase(j->second);
+      evict_count--;
+      if (!evict_count)
+        break;
+    }
+  }
+
+ public:
+  RandomCache(size_t max_size=20) : lock("RandomCache::lock"),
+                                    max_size(max_size) {}
+  ~RandomCache() {
+    contents.clear();
+  }
+
+  void clear(K key) {
+    Mutex::Locker l(lock);
+    contents.erase(key);
+  }
+
+  void set_size(size_t new_size) {
+    Mutex::Locker l(lock);
+    max_size = new_size;
+    if (max_size <= contents.size()) {
+      trim_cache(contents.size() - max_size);
+    }
+  }
+
+  bool lookup(K key, V *out) {
+    Mutex::Locker l(lock);
+    typename ceph::unordered_map<K, pair<uint64_t, V> >::iterator it = contents.find(key);
+    if (it != contents.end()) {
+      it->second.first++;
+      *out = it->second.second;
+      return true;
+    }
+    return false;
+  }
+
+  void add(K key, V value) {
+    Mutex::Locker l(lock);
+    if (max_size <= contents.size()) {
+      trim_cache(EVICT_COUNT);
+    }
+    contents[key] = make_pair(1, value);
+  }
+};
+
+#endif