system/core: change LruCache to use unordered_set instead of BasicHashTable

Towards deprecation of BasicHashTable

Change-Id: I3f3d904636a85a794cccf972f6e4a94e7f3808f5

include/utils/LruCache.h

@@ -17,8 +17,11 @@
 #ifndef ANDROID_UTILS_LRU_CACHE_H
 #define ANDROID_UTILS_LRU_CACHE_H
 
+#include <unordered_set>
+
 #include <UniquePtr.h>
-#include <utils/BasicHashtable.h>
+
+#include "utils/TypeHelpers.h"  // hash_t
 
 namespace android {
 
@@ -36,6 +39,7 @@ template <typename TKey, typename TValue>
 class LruCache {
 public:
     explicit LruCache(uint32_t maxCapacity);
+    virtual ~LruCache();
 
     enum Capacity {
         kUnlimitedCapacity,
@@ -50,32 +54,6 @@ public:
     void clear();
     const TValue& peekOldestValue();
 
-    class Iterator {
-    public:
-        Iterator(const LruCache<TKey, TValue>& cache): mCache(cache), mIndex(-1) {
-        }
-
-        bool next() {
-            mIndex = mCache.mTable->next(mIndex);
-            return (ssize_t)mIndex != -1;
-        }
-
-        size_t index() const {
-            return mIndex;
-        }
-
-        const TValue& value() const {
-            return mCache.mTable->entryAt(mIndex).value;
-        }
-
-        const TKey& key() const {
-            return mCache.mTable->entryAt(mIndex).key;
-        }
-    private:
-        const LruCache<TKey, TValue>& mCache;
-        size_t mIndex;
-    };
-
 private:
     LruCache(const LruCache& that);  // disallow copy constructor
 
@@ -90,27 +68,79 @@ private:
         const TKey& getKey() const { return key; }
     };
 
+    struct HashForEntry : public std::unary_function<Entry*, hash_t> {
+        size_t operator() (const Entry* entry) const {
+            return hash_type(entry->key);
+        };
+    };
+
+    struct EqualityForHashedEntries : public std::unary_function<Entry*, hash_t> {
+        bool operator() (const Entry* lhs, const Entry* rhs) const {
+            return lhs->key == rhs->key;
+        };
+    };
+
+    typedef std::unordered_set<Entry*, HashForEntry, EqualityForHashedEntries> LruCacheSet;
+
     void attachToCache(Entry& entry);
     void detachFromCache(Entry& entry);
-    void rehash(size_t newCapacity);
 
-    UniquePtr<BasicHashtable<TKey, Entry> > mTable;
+    typename LruCacheSet::iterator findByKey(const TKey& key) {
+        Entry entryForSearch(key, mNullValue);
+        typename LruCacheSet::iterator result = mSet->find(&entryForSearch);
+        return result;
+    }
+
+    UniquePtr<LruCacheSet> mSet;
     OnEntryRemoved<TKey, TValue>* mListener;
     Entry* mOldest;
     Entry* mYoungest;
     uint32_t mMaxCapacity;
     TValue mNullValue;
+
+public:
+    class Iterator {
+    public:
+        Iterator(const LruCache<TKey, TValue>& cache): mCache(cache), mIterator(mCache.mSet->begin()) {
+        }
+
+        bool next() {
+            if (mIterator == mCache.mSet->end()) {
+                return false;
+            }
+            std::advance(mIterator, 1);
+            return mIterator != mCache.mSet->end();
+        }
+
+        const TValue& value() const {
+            return (*mIterator)->value;
+        }
+
+        const TKey& key() const {
+            return (*mIterator)->key;
+        }
+    private:
+        const LruCache<TKey, TValue>& mCache;
+        typename LruCacheSet::iterator mIterator;
+    };
 };
 
 // Implementation is here, because it's fully templated
 template <typename TKey, typename TValue>
 LruCache<TKey, TValue>::LruCache(uint32_t maxCapacity)
-    : mTable(new BasicHashtable<TKey, Entry>)
+    : mSet(new LruCacheSet())
     , mListener(NULL)
     , mOldest(NULL)
     , mYoungest(NULL)
     , mMaxCapacity(maxCapacity)
     , mNullValue(NULL) {
+    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>
@@ -120,20 +150,19 @@ void LruCache<K, V>::setOnEntryRemovedListener(OnEntryRemoved<K, V>* listener) {
 
 template <typename TKey, typename TValue>
 size_t LruCache<TKey, TValue>::size() const {
-    return mTable->size();
+    return mSet->size();
 }
 
 template <typename TKey, typename TValue>
 const TValue& LruCache<TKey, TValue>::get(const TKey& key) {
-    hash_t hash = hash_type(key);
-    ssize_t index = mTable->find(-1, hash, key);
-    if (index == -1) {
+    typename LruCacheSet::const_iterator find_result = findByKey(key);
+    if (find_result == mSet->end()) {
         return mNullValue;
     }
-    Entry& entry = mTable->editEntryAt(index);
-    detachFromCache(entry);
-    attachToCache(entry);
-    return entry.value;
+    Entry *entry = *find_result;
+    detachFromCache(*entry);
+    attachToCache(*entry);
+    return entry->value;
 }
 
 template <typename TKey, typename TValue>
@@ -142,36 +171,29 @@ bool LruCache<TKey, TValue>::put(const TKey& key, const TValue& value) {
         removeOldest();
     }
 
-    hash_t hash = hash_type(key);
-    ssize_t index = mTable->find(-1, hash, key);
-    if (index >= 0) {
+    if (findByKey(key) != mSet->end()) {
         return false;
     }
-    if (!mTable->hasMoreRoom()) {
-        rehash(mTable->capacity() * 2);
-    }
 
-    // Would it be better to initialize a blank entry and assign key, value?
-    Entry initEntry(key, value);
-    index = mTable->add(hash, initEntry);
-    Entry& entry = mTable->editEntryAt(index);
-    attachToCache(entry);
+    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) {
-    hash_t hash = hash_type(key);
-    ssize_t index = mTable->find(-1, hash, key);
-    if (index < 0) {
+    typename LruCacheSet::const_iterator find_result = findByKey(key);
+    if (find_result == mSet->end()) {
         return false;
     }
-    Entry& entry = mTable->editEntryAt(index);
+    Entry* entry = *find_result;
     if (mListener) {
-        (*mListener)(entry.key, entry.value);
+        (*mListener)(entry->key, entry->value);
     }
-    detachFromCache(entry);
-    mTable->removeAt(index);
+    detachFromCache(*entry);
+    mSet->erase(entry);
+    delete entry;
     return true;
 }
 
@@ -201,7 +223,10 @@ void LruCache<TKey, TValue>::clear() {
     }
     mYoungest = NULL;
     mOldest = NULL;
-    mTable->clear();
+    for (auto entry : *mSet.get()) {
+        delete entry;
+    }
+    mSet->clear();
 }
 
 template <typename TKey, typename TValue>
@@ -232,19 +257,5 @@ void LruCache<TKey, TValue>::detachFromCache(Entry& entry) {
     entry.child = NULL;
 }
 
-template <typename TKey, typename TValue>
-void LruCache<TKey, TValue>::rehash(size_t newCapacity) {
-    UniquePtr<BasicHashtable<TKey, Entry> > oldTable(mTable.release());
-    Entry* oldest = mOldest;
-
-    mOldest = NULL;
-    mYoungest = NULL;
-    mTable.reset(new BasicHashtable<TKey, Entry>(newCapacity));
-    for (Entry* p = oldest; p != NULL; p = p->child) {
-        put(p->key, p->value);
-    }
 }
-
-}
-
 #endif // ANDROID_UTILS_LRU_CACHE_H

libutils/tests/LruCache_test.cpp

@@ -221,7 +221,7 @@ TEST_F(LruCacheTest, NoLeak) {
     cache.put(ComplexKey(0), ComplexValue(0));
     cache.put(ComplexKey(1), ComplexValue(1));
     EXPECT_EQ(2U, cache.size());
-    assertInstanceCount(2, 3);  // the null value counts as an instance
+    assertInstanceCount(2, 3);  // the member mNullValue counts as an instance
 }
 
 TEST_F(LruCacheTest, Clear) {