wip: refactore

src/xrpld/core/detail/LRUMap.h

@@ -20,73 +20,114 @@
 #ifndef RIPPLE_APP_LRU_MAP_H_INCLUDED
 #define RIPPLE_APP_LRU_MAP_H_INCLUDED
 
+#include <cstddef>
 #include <list>
-#include <map>
+#include <stdexcept>
+#include <unordered_map>
 #include <utility>
 
 namespace ripple {
 
-template <typename Key, typename Value>
+template <
+    class Key,
+    class Value,
+    class Hash = std::hash<Key>,
+    class KeyEq = std::equal_to<Key>>
 class LRUMap
 {
+    using List = std::list<Key>;
+    using DataMap = std::unordered_map<Key, Value, Hash, KeyEq>;
+    using PosMap =
+        std::unordered_map<Key, typename List::iterator, Hash, KeyEq>;
+
 public:
     explicit LRUMap(std::size_t capacity) : capacity_(capacity)
     {
-        // TODO: check capacity_ > 0
+        if (!capacity_)
+            throw std::invalid_argument(
+                "LRUMap capacity must be positive.");  // TODO XRPL_ASSERT
+        data_.reserve(capacity_);
+        pos_.reserve(capacity_);
     }
 
     Value&
     operator[](Key const& key)
     {
-        auto it = data_.find(key);
-        if (it != data_.end())
+        if (auto it = data_.find(key); it != data_.end())
         {
-            bump_to_front(key);
+            auto lit = pos_.at(key);
+            // promote
+            usage_.splice(usage_.begin(), usage_, lit);
             return it->second;
         }
 
         if (data_.size() >= capacity_)
         {
-            std::size_t excess = (data_.size() + 1) - capacity_;
-            for (std::size_t i = 0; i < excess; ++i)
-            {
-                auto lru = usage_list_.back();
-                usage_list_.pop_back();
-                data_.erase(lru);
-            }
+            auto const& lru_key = usage_.back();
+            data_.erase(lru_key);
+            pos_.erase(lru_key);
+            usage_.pop_back();
         }
 
-        usage_list_.push_front(key);
-        return data_[key];
+        usage_.emplace_front(key);
+        pos_.emplace(key, usage_.begin());
+        auto [it, _] = data_.emplace(key, Value{});
+        return it->second;
     }
 
-    auto
+    Value*
+    get(Key const& key)
+    {
+        auto it = data_.find(key);
+        if (it == data_.end())
+            return nullptr;
+        auto lit = pos_.at(key);
+        usage_.splice(usage_.begin(), usage_, lit);
+        return &it->second;
+    }
+
+    // TODO: remove
+    Value const*
+    peek(Key const& key) const
+    {
+        auto it = data_.find(key);
+        return it == data_.end() ? nullptr : &it->second;
+    }
+
+    using iterator = typename DataMap::iterator;
+    using const_iterator = typename DataMap::const_iterator;
+
+    iterator
     find(Key const& key)
     {
         return data_.find(key);
     }
-    auto
+
+    const_iterator
     find(Key const& key) const
     {
         return data_.find(key);
     }
 
-    auto
+    iterator
     begin()
     {
         return data_.begin();
     }
-    auto
+
+    const_iterator
     begin() const
     {
         return data_.begin();
     }
-    auto
+
+    iterator
     end()
     {
         return data_.end();
     }
-    auto
+
+    const_iterator
     end() const
     {
         return data_.end();
@@ -98,54 +139,73 @@ public:
         auto it = data_.find(key);
         if (it == data_.end())
             return false;
-        for (auto list_it = usage_list_.begin(); list_it != usage_list_.end();
-             ++list_it)
-        {
-            if (*list_it == key)
-            {
-                usage_list_.erase(list_it);
-                break;
-            }
-        }
+        usage_.erase(pos_.at(key));
+        pos_.erase(key);
         data_.erase(it);
         return true;
     }
 
+    template <class... Args>
+    Value&
+    put(Key const& key, Args&&... args)  // assign/construct + promote
+    {
+        if (auto it = data_.find(key); it != data_.end())
+        {
+            it->second = Value(std::forward<Args>(args)...);
+            auto lit = pos_.at(key);
+            usage_.splice(usage_.begin(), usage_, lit);
+            return it->second;
+        }
+        if (data_.size() >= capacity_)
+        {
+            auto const& lru_key = usage_.back();
+            data_.erase(lru_key);
+            pos_.erase(lru_key);
+            usage_.pop_back();
+        }
+        usage_.emplace_front(key);
+        pos_.emplace(key, usage_.begin());
+        auto [it, _] = data_.emplace(key, Value(std::forward<Args>(args)...));
+        return it->second;
+    }
+
+    bool
+    contains(Key const& key) const
+    {
+        return data_.find(key) != data_.end();
+    }
+
     std::size_t
     size() const noexcept
     {
         return data_.size();
     }
+
     std::size_t
     capacity() const noexcept
     {
         return capacity_;
     }
+
+    bool
+    empty() const noexcept
+    {
+        return data_.empty();
+    }
+
     void
     clear()
     {
         data_.clear();
-        usage_list_.clear();
+        pos_.clear();
+        usage_.clear();
     }
 
 private:
-    void
-    bump_to_front(Key const& key)
-    {
-        for (auto it = usage_list_.begin(); it != usage_list_.end(); ++it)
-        {
-            if (*it == key)
-            {
-                usage_list_.erase(it);
-                usage_list_.push_front(key);
-                return;
-            }
-        }
-    }
-
-    std::size_t capacity_;
-    std::map<Key, Value> data_;
-    std::list<Key> usage_list_;
+    std::size_t const capacity_;
+    DataMap data_;  // Key -> Value   (this is what callers iterate/find over)
+    PosMap pos_;    // Key -> list position
+    List usage_;    // recency order
 };
 
 }  // namespace ripple