1 files changed, 191 insertions, 0 deletions
diff --git a/src/common/intrusive_lru.h b/src/common/intrusive_lru.h
new file mode 100644
index 000000000..422c24a14
--- /dev/null
+++ b/src/common/intrusive_lru.h
@@ -0,0 +1,191 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#pragma once
+
+#include <boost/intrusive_ptr.hpp>
+#include <boost/intrusive/set.hpp>
+#include <boost/intrusive/list.hpp>
+
+namespace ceph::common {
+
+/**
+ * intrusive_lru: lru implementation with embedded map and list hook
+ *
+ * Note, this implementation currently is entirely thread-unsafe.
+ */
+
+template <typename K, typename V, typename VToK>
+struct intrusive_lru_config {
+  using key_type = K;
+  using value_type = V;
+  using key_of_value = VToK;
+};
+
+template <typename Config>
+class intrusive_lru;
+
+template <typename Config>
+class intrusive_lru_base;
+
+template <typename Config>
+void intrusive_ptr_add_ref(intrusive_lru_base<Config> *p);
+
+template <typename Config>
+void intrusive_ptr_release(intrusive_lru_base<Config> *p);
+
+
+template <typename Config>
+class intrusive_lru_base {
+  unsigned use_count = 0;
+
+  // null if unreferenced
+  intrusive_lru<Config> *lru = nullptr;
+
+public:
+  boost::intrusive::set_member_hook<> set_hook;
+  boost::intrusive::list_member_hook<> list_hook;
+
+  using Ref = boost::intrusive_ptr<typename Config::value_type>;
+  using lru_t = intrusive_lru<Config>;
+
+  friend intrusive_lru<Config>;
+  friend void intrusive_ptr_add_ref<>(intrusive_lru_base<Config> *);
+  friend void intrusive_ptr_release<>(intrusive_lru_base<Config> *);
+
+  virtual ~intrusive_lru_base() {}
+};
+
+template <typename Config>
+class intrusive_lru {
+  using base_t = intrusive_lru_base<Config>;
+  using K = typename Config::key_type;
+  using T = typename Config::value_type;
+  using TRef = typename base_t::Ref;
+
+  using lru_set_option_t = boost::intrusive::member_hook<
+    base_t,
+    boost::intrusive::set_member_hook<>,
+    &base_t::set_hook>;
+
+  using VToK = typename Config::key_of_value;
+  struct VToKWrapped {
+    using type = typename VToK::type;
+    const type &operator()(const base_t &obc) {
+      return VToK()(static_cast<const T&>(obc));
+    }
+  };
+  using lru_set_t = boost::intrusive::set<
+    base_t,
+    lru_set_option_t,
+    boost::intrusive::key_of_value<VToKWrapped>
+    >;
+  lru_set_t lru_set;
+
+  using lru_list_t = boost::intrusive::list<
+    base_t,
+    boost::intrusive::member_hook<
+      base_t,
+      boost::intrusive::list_member_hook<>,
+      &base_t::list_hook>>;
+  lru_list_t unreferenced_list;
+
+  size_t lru_target_size = 0;
+
+  void evict() {
+    while (!unreferenced_list.empty() &&
+	   lru_set.size() > lru_target_size) {
+      auto &b = unreferenced_list.front();
+      assert(!b.lru);
+      unreferenced_list.pop_front();
+      lru_set.erase_and_dispose(
+	lru_set.iterator_to(b),
+	[](auto *p) { delete p; }
+      );
+    }
+  }
+
+  void access(base_t &b) {
+    if (b.lru)
+      return;
+    unreferenced_list.erase(lru_list_t::s_iterator_to(b));
+    b.lru = this;
+  }
+
+  void insert(base_t &b) {
+    assert(!b.lru);
+    lru_set.insert(b);
+    b.lru = this;
+    evict();
+  }
+
+  void unreferenced(base_t &b) {
+    assert(b.lru);
+    unreferenced_list.push_back(b);
+    b.lru = nullptr;
+    evict();
+  }
+
+public:
+  /**
+   * Returns the TRef corresponding to k if it exists or
+   * creates it otherwise.  Return is:
+   * std::pair(reference_to_val, found)
+   */
+  std::pair<TRef, bool> get_or_create(const K &k) {
+    typename lru_set_t::insert_commit_data icd;
+    auto [iter, missing] = lru_set.insert_check(
+      k,
+      icd);
+    if (missing) {
+      auto ret = new T(k);
+      lru_set.insert_commit(*ret, icd);
+      insert(*ret);
+      return {TRef(ret), false};
+    } else {
+      access(*iter);
+      return {TRef(static_cast<T*>(&*iter)), true};
+    }
+  }
+
+  /**
+   * Returns the TRef corresponding to k if it exists or
+   * nullptr otherwise.
+   */
+  TRef get(const K &k) {
+    if (auto iter = lru_set.find(k); iter != std::end(lru_set)) {
+      access(*iter);
+      return TRef(static_cast<T*>(&*iter));
+    } else {
+      return nullptr;
+    }
+  }
+
+  void set_target_size(size_t target_size) {
+    lru_target_size = target_size;
+    evict();
+  }
+
+  friend void intrusive_ptr_add_ref<>(intrusive_lru_base<Config> *);
+  friend void intrusive_ptr_release<>(intrusive_lru_base<Config> *);
+};
+
+template <typename Config>
+void intrusive_ptr_add_ref(intrusive_lru_base<Config> *p) {
+  assert(p);
+  assert(p->lru);
+  p->use_count++;
+}
+
+template <typename Config>
+void intrusive_ptr_release(intrusive_lru_base<Config> *p) {
+  assert(p);
+  assert(p->use_count > 0);
+  --p->use_count;
+  if (p->use_count == 0) {
+    p->lru->unreferenced(*p);
+  }
+}
+
+
+}