Merge "Exporting C++ headers from system/core" am: 812b7d5d52 am: f484dd3401

am: a252f11da3

Change-Id: If2dc2da283db7a60f478c6e61a9e9b32edb42ce7

1 files changed, 298 insertions, 0 deletions

diff --git a/libutils/include/utils/LruCache.h b/libutils/include/utils/LruCache.h
new file mode 100644
index 000000000..89dccd613
--- /dev/null
+++ b/libutils/include/utils/LruCache.h
@@ -0,0 +1,298 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_UTILS_LRU_CACHE_H
+#define ANDROID_UTILS_LRU_CACHE_H
+
+#include <memory>
+#include <unordered_set>
+
+#include "utils/TypeHelpers.h"  // hash_t
+
+namespace android {
+
+/**
+ * GenerationCache callback used when an item is removed
+ */
+template<typename EntryKey, typename EntryValue>
+class OnEntryRemoved {
+public:
+    virtual ~OnEntryRemoved() { };
+    virtual void operator()(EntryKey& key, EntryValue& value) = 0;
+}; // class OnEntryRemoved
+
+template <typename TKey, typename TValue>
+class LruCache {
+public:
+    explicit LruCache(uint32_t maxCapacity);
+    virtual ~LruCache();
+
+    enum Capacity {
+        kUnlimitedCapacity,
+    };
+
+    void setOnEntryRemovedListener(OnEntryRemoved<TKey, TValue>* listener);
+    size_t size() const;
+    const TValue& get(const TKey& key);
+    bool put(const TKey& key, const TValue& value);
+    bool remove(const TKey& key);
+    bool removeOldest();
+    void clear();
+    const TValue& peekOldestValue();
+
+private:
+    LruCache(const LruCache& that);  // disallow copy constructor
+
+    // Super class so that we can have entries having only a key reference, for searches.
+    class KeyedEntry {
+    public:
+        virtual const TKey& getKey() const = 0;
+        // Make sure the right destructor is executed so that keys and values are deleted.
+        virtual ~KeyedEntry() {}
+    };
+
+    class Entry final : public KeyedEntry {
+    public:
+        TKey key;
+        TValue value;
+        Entry* parent;
+        Entry* child;
+
+        Entry(TKey _key, TValue _value) : key(_key), value(_value), parent(NULL), child(NULL) {
+        }
+        const TKey& getKey() const final { return key; }
+    };
+
+    class EntryForSearch : public KeyedEntry {
+    public:
+        const TKey& key;
+        EntryForSearch(const TKey& key_) : key(key_) {
+        }
+        const TKey& getKey() const final { return key; }
+    };
+
+    struct HashForEntry : public std::unary_function<KeyedEntry*, hash_t> {
+        size_t operator() (const KeyedEntry* entry) const {
+            return hash_type(entry->getKey());
+        };
+    };
+
+    struct EqualityForHashedEntries : public std::unary_function<KeyedEntry*, hash_t> {
+        bool operator() (const KeyedEntry* lhs, const KeyedEntry* rhs) const {
+            return lhs->getKey() == rhs->getKey();
+        };
+    };
+
+    // All entries in the set will be Entry*. Using the weaker KeyedEntry as to allow entries
+    // that have only a key reference, for searching.
+    typedef std::unordered_set<KeyedEntry*, HashForEntry, EqualityForHashedEntries> LruCacheSet;
+
+    void attachToCache(Entry& entry);
+    void detachFromCache(Entry& entry);
+
+    typename LruCacheSet::iterator findByKey(const TKey& key) {
+        EntryForSearch entryForSearch(key);
+        typename LruCacheSet::iterator result = mSet->find(&entryForSearch);
+        return result;
+    }
+
+    std::unique_ptr<LruCacheSet> mSet;
+    OnEntryRemoved<TKey, TValue>* mListener;
+    Entry* mOldest;
+    Entry* mYoungest;
+    uint32_t mMaxCapacity;
+    TValue mNullValue;
+
+public:
+    // To be used like:
+    // while (it.next()) {
+    //   it.value(); it.key();
+    // }
+    class Iterator {
+    public:
+        Iterator(const LruCache<TKey, TValue>& cache):
+                mCache(cache), mIterator(mCache.mSet->begin()), mBeginReturned(false) {
+        }
+
+        bool next() {
+            if (mIterator == mCache.mSet->end()) {
+                return false;
+            }
+            if (!mBeginReturned) {
+                // mIterator has been initialized to the beginning and
+                // hasn't been returned. Do not advance:
+                mBeginReturned = true;
+            } else {
+                std::advance(mIterator, 1);
+            }
+            bool ret = (mIterator != mCache.mSet->end());
+            return ret;
+        }
+
+        const TValue& value() const {
+            // All the elements in the set are of type Entry. See comment in the definition
+            // of LruCacheSet above.
+            return reinterpret_cast<Entry *>(*mIterator)->value;
+        }
+
+        const TKey& key() const {
+            return (*mIterator)->getKey();
+        }
+    private:
+        const LruCache<TKey, TValue>& mCache;
+        typename LruCacheSet::iterator mIterator;
+        bool mBeginReturned;
+    };
+};
+
+// Implementation is here, because it's fully templated
+template <typename TKey, typename TValue>
+LruCache<TKey, TValue>::LruCache(uint32_t maxCapacity)
+    : mSet(new LruCacheSet())
+    , mListener(NULL)
+    , mOldest(NULL)
+    , mYoungest(NULL)
+    , mMaxCapacity(maxCapacity)
+    , mNullValue(0) {
+    mSet->max_load_factor(1.0);
+};
+
+template <typename TKey, typename TValue>
+LruCache<TKey, TValue>::~LruCache() {
+    // Need to delete created entries.
+    clear();
+};
+
+template<typename K, typename V>
+void LruCache<K, V>::setOnEntryRemovedListener(OnEntryRemoved<K, V>* listener) {
+    mListener = listener;
+}
+
+template <typename TKey, typename TValue>
+size_t LruCache<TKey, TValue>::size() const {
+    return mSet->size();
+}
+
+template <typename TKey, typename TValue>
+const TValue& LruCache<TKey, TValue>::get(const TKey& key) {
+    typename LruCacheSet::const_iterator find_result = findByKey(key);
+    if (find_result == mSet->end()) {
+        return mNullValue;
+    }
+    // All the elements in the set are of type Entry. See comment in the definition
+    // of LruCacheSet above.
+    Entry *entry = reinterpret_cast<Entry*>(*find_result);
+    detachFromCache(*entry);
+    attachToCache(*entry);
+    return entry->value;
+}
+
+template <typename TKey, typename TValue>
+bool LruCache<TKey, TValue>::put(const TKey& key, const TValue& value) {
+    if (mMaxCapacity != kUnlimitedCapacity && size() >= mMaxCapacity) {
+        removeOldest();
+    }
+
+    if (findByKey(key) != mSet->end()) {
+        return false;
+    }
+
+    Entry* newEntry = new Entry(key, value);
+    mSet->insert(newEntry);
+    attachToCache(*newEntry);
+    return true;
+}
+
+template <typename TKey, typename TValue>
+bool LruCache<TKey, TValue>::remove(const TKey& key) {
+    typename LruCacheSet::const_iterator find_result = findByKey(key);
+    if (find_result == mSet->end()) {
+        return false;
+    }
+    // All the elements in the set are of type Entry. See comment in the definition
+    // of LruCacheSet above.
+    Entry* entry = reinterpret_cast<Entry*>(*find_result);
+    mSet->erase(entry);
+    if (mListener) {
+        (*mListener)(entry->key, entry->value);
+    }
+    detachFromCache(*entry);
+    delete entry;
+    return true;
+}
+
+template <typename TKey, typename TValue>
+bool LruCache<TKey, TValue>::removeOldest() {
+    if (mOldest != NULL) {
+        return remove(mOldest->key);
+        // TODO: should probably abort if false
+    }
+    return false;
+}
+
+template <typename TKey, typename TValue>
+const TValue& LruCache<TKey, TValue>::peekOldestValue() {
+    if (mOldest) {
+        return mOldest->value;
+    }
+    return mNullValue;
+}
+
+template <typename TKey, typename TValue>
+void LruCache<TKey, TValue>::clear() {
+    if (mListener) {
+        for (Entry* p = mOldest; p != NULL; p = p->child) {
+            (*mListener)(p->key, p->value);
+        }
+    }
+    mYoungest = NULL;
+    mOldest = NULL;
+    for (auto entry : *mSet.get()) {
+        delete entry;
+    }
+    mSet->clear();
+}
+
+template <typename TKey, typename TValue>
+void LruCache<TKey, TValue>::attachToCache(Entry& entry) {
+    if (mYoungest == NULL) {
+        mYoungest = mOldest = &entry;
+    } else {
+        entry.parent = mYoungest;
+        mYoungest->child = &entry;
+        mYoungest = &entry;
+    }
+}
+
+template <typename TKey, typename TValue>
+void LruCache<TKey, TValue>::detachFromCache(Entry& entry) {
+    if (entry.parent != NULL) {
+        entry.parent->child = entry.child;
+    } else {
+        mOldest = entry.child;
+    }
+    if (entry.child != NULL) {
+        entry.child->parent = entry.parent;
+    } else {
+        mYoungest = entry.parent;
+    }
+
+    entry.parent = NULL;
+    entry.child = NULL;
+}
+
+}
+#endif // ANDROID_UTILS_LRU_CACHE_H