400 lines of code to implement local Key-Value Cache

There are many Key-Value caches, most of which are memcache and redis. They all run in the form of independent services. At work, sometimes a local key-value cache needs to be embedded, of course there are already LevelDb and so on, but it still feels too heavyweight.

This article implements a super lightweight cache,

1. Only 400 lines of code are required;

2. High performance. The testing speed is about 2 million per second when the value length is 1 K.

3. the cache is mapped to files, so there is no malloc or free overhead, as well as Memory leakage and memory fragmentation;

4. If the service fails, the cached content continues to exist after restart;

5. If the cache is mapped to a disk file, even if the machine crashes, the cached content will still exist. Of course, data corruption may occur;

6. To a certain extent, the LRU elimination algorithm is implemented. The LRU is implemented on a chain instead of a global one, so it can only be said to be implemented in a certain program;

7. It is stable and has been used in multiple projects. There are dozens of machines deployed online, and no problems have occurred after nearly half a year of operation;

8. Common cache keys and values are strings. The cached keys and values can be class and struct Object Structures for ease of use;

The old rule goes directly to the Code:

template<typename K, typename V>class HashTable{public:    HashTable(const char *tablename, uint32_t tableLen, uint32_t nodeTotal);    virtual ~HashTable();    bool Add(K &key, V &value)    {        AutoLock autoLock(m_MutexLock);        //check is exist        uint32_t nodeId = GetIdByKey(key);        if(nodeId != m_InvalidId) return false;        nodeId = GetFreeNode();        if(nodeId == m_InvalidId) return false;        uint32_t hashCode = key.HashCode();        Entry *tmpNode = m_EntryAddr + nodeId;        tmpNode->m_Key = key;        tmpNode->m_Code = hashCode;        tmpNode->m_Value = value;        uint32_t index = hashCode % m_HeadAddr->m_TableLen;        AddNodeToHead(index, nodeId);        return true;    }        bool Del(K &key)    {        AutoLock autoLock(m_MutexLock);        uint32_t nodeId = GetIdByKey(key);        if(nodeId == m_InvalidId) return false;                uint32_t index = key.HashCode() % m_HeadAddr->m_TableLen;                return RecycleNode(index, nodeId);    }    bool Set(K &key, V &value)    {        AutoLock autoLock(m_MutexLock);                uint32_t nodeId = GetIdByKey(key);        if(nodeId == m_InvalidId) return false;        (m_EntryAddr + nodeId)->m_Value = value;        return true;    }            bool Get(K &key, V &value)    {        AutoLock autoLock(m_MutexLock);                uint32_t nodeId = GetIdByKey(key);        if(nodeId == m_InvalidId) return false;        value = (m_EntryAddr + nodeId)->m_Value;        return true;    }        bool Exist(K &key)    {        AutoLock autoLock(m_MutexLock);                uint32_t nodeId = GetIdByKey(key);        if(nodeId == m_InvalidId) return false;        return true;    }    uint32_t Count()    {        AutoLock autoLock(m_MutexLock);        return m_HeadAddr->m_UsedCount;    }    //if exist set else add    bool Replace(K &key, V &value)    {        AutoLock autoLock(m_MutexLock);                if(Exist(key)) return Set(key, value);        else return Add(key, value);    }    /***********************************************    ****LRU: when visit a node, move it to head ****    ************************************************/    //if no empty place,recycle tail    bool LruAdd(K &key, V &value, K &recyKey, V &recyValue, bool &recycled)    {        AutoLock autoLock(m_MutexLock);                if(Exist(key)) return false;        if(Add(key, value)) return true;        uint32_t index = key.HashCode() % m_HeadAddr->m_TableLen;        uint32_t tailId = GetTailNodeId(index);                if(tailId == m_InvalidId) return false;                Entry *tmpNode = m_EntryAddr + tailId;        recyKey   = tmpNode->m_Key;        recyValue = tmpNode->m_Value;        recycled  = true;        RecycleNode(index, tailId);                return Add(key, value);    }        bool LruSet(K &key, V &value)    {        AutoLock autoLock(m_MutexLock);        if(Set(key, value)) return MoveToHead(key);        else return false;    }        bool LruGet(K &key, V &value)    {        AutoLock autoLock(m_MutexLock);            if(Get(key, value)) return MoveToHead(key);        else return false;    }    //if exist set else add; if add failed recycle tail than add    bool LruReplace(K &key, V &value, K &recyKey, V &recyValue, bool &recycled)    {        AutoLock autoLock(m_MutexLock);        recycled = false;                if(Exist(key)) return LruSet(key, value);        else return LruAdd(key, value, recyKey, recyValue, recycled);    }    void Clear()    {        AutoLock autoLock(m_MutexLock);                m_HeadAddr->m_FreeBase = 0;        m_HeadAddr->m_RecycleHead = 0;        m_HeadAddr->m_UsedCount = 0;        for(uint32_t i = 0; i < m_HeadAddr->m_TableLen; ++i)        {            (m_ArrayAddr+i)->m_Head = m_InvalidId;            (m_ArrayAddr+i)->m_Tail = m_InvalidId;        }    }    int GetRowKeys(vector<K> &keys, uint32_t index)    {        AutoLock autoLock(m_MutexLock);                if(index >= m_HeadAddr->m_TableLen) return -1;        keys.clear();        keys.reserve(16);                int count = 0;        Array *tmpArray = m_ArrayAddr + index;        uint32_t nodeId = tmpArray->m_Head;        while(nodeId != m_InvalidId)        {            Entry *tmpNode = m_EntryAddr + nodeId;            keys.push_back(tmpNode->m_Key);            nodeId = tmpNode->m_Next;            ++count;        }        return count;    }        void *Padding(uint32_t size)    {        AutoLock autoLock(m_MutexLock);        if(size > m_HeadSize - sizeof(TableHead)) return NULL;        else return m_HeadAddr->m_Padding;    }private:    static const uint32_t m_InvalidId = 0xffffffff;    static const uint32_t m_HeadSize = 1024;    struct TableHead    {        uint32_t m_TableLen;        uint32_t m_NodeTotal;        uint32_t m_FreeBase;        uint32_t m_RecycleHead;        uint32_t m_UsedCount;        char     m_TableName[256];        uint32_t m_Padding[0];    };    struct Array    {        uint32_t m_Head;        uint32_t m_Tail;    };    struct Entry    {        V m_Value;        K m_Key;        uint32_t m_Code;        uint32_t m_Next;        uint32_t m_Prev;    };        size_t     m_MemSize;    uint8_t   *m_MemAddr;    TableHead *m_HeadAddr;    Array     *m_ArrayAddr;    Entry     *m_EntryAddr;    ThreadMutex m_MutexLock;    bool MoveToHead(K &key);    uint32_t GetIdByKey(K &key);    void AddNodeToHead(uint32_t index, uint32_t nodeId);    bool MoveNodeToHead(uint32_t index, uint32_t nodeId);    bool RecycleNode(uint32_t index, uint32_t nodeId);    uint32_t GetTailNodeId(uint32_t index);    uint32_t GetFreeNode();    DISABLE_COPY_AND_ASSIGN(HashTable);};template<typename K, typename V>HashTable<K, V>::HashTable(const char *tablename, uint32_t tableLen, uint32_t nodeTotal){    AbortAssert(tablename != NULL);    m_MemSize = m_HeadSize + tableLen*sizeof(Array) + nodeTotal*sizeof(Entry);    m_MemAddr = (uint8_t*)MemFile::Realloc(tablename, m_MemSize);    AbortAssert(m_MemAddr != NULL);    m_HeadAddr = (TableHead*)(m_MemAddr);    m_ArrayAddr = (Array*)(m_MemAddr + m_HeadSize);    m_EntryAddr = (Entry*)(m_MemAddr + m_HeadSize + tableLen*sizeof(Array));    m_HeadAddr->m_TableLen = tableLen;    m_HeadAddr->m_NodeTotal = nodeTotal;    strncpy(m_HeadAddr->m_TableName, tablename, sizeof(m_HeadAddr->m_TableName));        if(m_HeadAddr->m_UsedCount == 0)//if first use init array to invalid id     {        for(uint32_t i = 0; i < tableLen; ++i)        {            (m_ArrayAddr+i)->m_Head = m_InvalidId;            (m_ArrayAddr+i)->m_Tail = m_InvalidId;        }        m_HeadAddr->m_FreeBase = 0;        m_HeadAddr->m_RecycleHead = 0;    }}template<typename K, typename V>HashTable<K, V>::~HashTable(){    MemFile::Release(m_MemAddr, m_MemSize);}template<typename K, typename V>bool HashTable<K, V>::MoveToHead(K &key){    uint32_t nodeId = GetIdByKey(key);    uint32_t index = key.HashCode() % m_HeadAddr->m_TableLen;    return MoveNodeToHead(index, nodeId);}template<typename K, typename V>uint32_t HashTable<K, V>::GetIdByKey(K &key){    uint32_t hashCode = key.HashCode();    uint32_t index = hashCode % m_HeadAddr->m_TableLen;    Array *tmpArray = m_ArrayAddr + index;        uint32_t nodeId = tmpArray->m_Head;    while(nodeId != m_InvalidId)    {        Entry *tmpNode = m_EntryAddr + nodeId;        if(tmpNode->m_Code == hashCode && key.Equals(tmpNode->m_Key)) break;                nodeId = tmpNode->m_Next;    }    return nodeId;}template<typename K, typename V>void HashTable<K, V>::AddNodeToHead(uint32_t index, uint32_t nodeId){    if(index >= m_HeadAddr->m_TableLen || nodeId >= m_HeadAddr->m_NodeTotal) return;    Array *tmpArray = m_ArrayAddr + index;    Entry *tmpNode = m_EntryAddr + nodeId;    if(m_InvalidId == tmpArray->m_Head)    {        tmpArray->m_Head = nodeId;        tmpArray->m_Tail = nodeId;    }    else    {        tmpNode->m_Next = tmpArray->m_Head;        (m_EntryAddr + tmpArray->m_Head)->m_Prev = nodeId;        tmpArray->m_Head = nodeId;    }}template<typename K, typename V>bool HashTable<K, V>::MoveNodeToHead(uint32_t index, uint32_t nodeId){    if(index >= m_HeadAddr->m_TableLen || nodeId >= m_HeadAddr->m_NodeTotal) return false;        Array *tmpArray = m_ArrayAddr + index;    Entry *tmpNode = m_EntryAddr + nodeId;        //already head    if(tmpArray->m_Head == nodeId)    {        return true;    }    uint32_t nodePrev = tmpNode->m_Prev;    uint32_t nodeNext = tmpNode->m_Next;    (m_EntryAddr+nodePrev)->m_Next = nodeNext;    if(nodeNext != m_InvalidId)    {        (m_EntryAddr+nodeNext)->m_Prev = nodePrev;    }    else    {        tmpArray->m_Tail = nodePrev;    }    tmpNode->m_Prev = m_InvalidId;    tmpNode->m_Next = tmpArray->m_Head;    (m_EntryAddr + tmpArray->m_Head)->m_Prev = nodeId;    tmpArray->m_Head = nodeId;    return true;}template<typename K, typename V>bool HashTable<K, V>::RecycleNode(uint32_t index, uint32_t nodeId){    if(index >= m_HeadAddr->m_TableLen || nodeId >= m_HeadAddr->m_NodeTotal) return false;        Array *tmpArray = m_ArrayAddr + index;    Entry *tmpNode = m_EntryAddr + nodeId;    uint32_t nodePrev = tmpNode->m_Prev;    uint32_t nodeNext = tmpNode->m_Next;    if(nodePrev != m_InvalidId)    {        (m_EntryAddr + nodePrev)->m_Next = nodeNext;    }    else    {        tmpArray->m_Head = nodeNext;    }    if(nodeNext != m_InvalidId)    {        (m_EntryAddr + nodeNext)->m_Prev = nodePrev;    }    else    {        tmpArray->m_Tail = nodePrev;    }    (m_EntryAddr+nodeId)->m_Next = m_HeadAddr->m_RecycleHead;    m_HeadAddr->m_RecycleHead = nodeId;    --(m_HeadAddr->m_UsedCount);    return true;}template<typename K, typename V>uint32_t HashTable<K, V>::GetTailNodeId(uint32_t index){    if(index >= m_HeadAddr->m_TableLen) return m_InvalidId;        Array *tmpArray = m_ArrayAddr + index;    return tmpArray->m_Tail;}template<typename K, typename V>uint32_t HashTable<K, V>::GetFreeNode(){    uint32_t nodeId = m_InvalidId;    if(m_HeadAddr->m_UsedCount < m_HeadAddr->m_FreeBase)//get from recycle list    {        nodeId = m_HeadAddr->m_RecycleHead;        m_HeadAddr->m_RecycleHead = (m_EntryAddr+nodeId)->m_Next;        ++(m_HeadAddr->m_UsedCount);    }    else if(m_HeadAddr->m_UsedCount < m_HeadAddr->m_NodeTotal)//get from free mem    {        nodeId = m_HeadAddr->m_FreeBase;        ++(m_HeadAddr->m_FreeBase);        ++(m_HeadAddr->m_UsedCount);    }    else    {        nodeId = m_InvalidId;    }    //init node    if(nodeId < m_HeadAddr->m_NodeTotal)    {        Entry *tmpNode = m_EntryAddr + nodeId;        memset(tmpNode, 0, sizeof(Entry));        tmpNode->m_Next = m_InvalidId;        tmpNode->m_Prev = m_InvalidId;    }        return nodeId;}