connection_pool.h

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#ifndef ENGINE_SERVER_DATABASES_CONNECTION_POOL_H
#define ENGINE_SERVER_DATABASES_CONNECTION_POOL_H
 
#include <base/sphore.h>
 
#include <atomic>
#include <memory>
#include <vector>
 
class IDbConnection;
 
struct ISqlResult
{
    // using atomic_bool to indicate completed sql query since usage_count
    // from shard_ptr isn't safe in multithreaded environment
    // the main thread must only access the remaining result data if set to true
    std::atomic_bool m_Completed{false};
    // indicate whether the thread indicated a successful completion (returned true)
    bool m_Success = false;
 
    virtual ~ISqlResult() = default;
};
 
struct ISqlData
{
    ISqlData(std::shared_ptr<ISqlResult> pResult) :
        m_pResult(std::move(pResult))
    {
    }
    virtual ~ISqlData() = default;
 
    mutable std::shared_ptr<ISqlResult> m_pResult;
};
 
enum Write
{
    // write everything into the backup db first
    BACKUP_FIRST,
    // now try to write it into remote db
    NORMAL,
    // succeeded writing -> remove copy from backup
    NORMAL_SUCCEEDED,
    // failed writing -> notify about failure
    NORMAL_FAILED,
};
 
struct CMysqlConfig
{
    char m_aDatabase[64];
    char m_aPrefix[64];
    char m_aUser[64];
    char m_aPass[64];
    char m_aIp[64];
    char m_aBindaddr[128];
    int m_Port;
    bool m_Setup;
};
 
class CDbConnectionPool
{
public:
    CDbConnectionPool();
    ~CDbConnectionPool();
    CDbConnectionPool &operator=(const CDbConnectionPool &) = delete;
 
    // Returns false on success.
    typedef bool (*FRead)(IDbConnection *, const ISqlData *, char *pError, int ErrorSize);
    typedef bool (*FWrite)(IDbConnection *, const ISqlData *, Write, char *pError, int ErrorSize);
 
    enum Mode
    {
        READ,
        WRITE,
        WRITE_BACKUP,
        NUM_MODES,
    };
 
    void Print(Mode DatabaseMode);
 
    void RegisterSqliteDatabase(Mode DatabaseMode, const char aFilename[64]);
    void RegisterMysqlDatabase(Mode DatabaseMode, const CMysqlConfig *pMysqlConfig);
 
    void Execute(
        FRead pFunc,
        std::unique_ptr<const ISqlData> pSqlRequestData,
        const char *pName);
    // writes to WRITE_BACKUP first and removes it from there when successfully
    // executed on WRITE server
    void ExecuteWrite(
        FWrite pFunc,
        std::unique_ptr<const ISqlData> pSqlRequestData,
        const char *pName);
 
    void OnShutdown();
 
    friend class CWorker;
    friend class CBackup;
 
private:
    static bool ExecSqlFunc(IDbConnection *pConnection, struct CSqlExecData *pData, Write w);
 
    // Only the main thread accesses this variable. It points to the index,
    // where the next query is added to the queue.
    int m_InsertIdx = 0;
 
    bool m_Shutdown = false;
 
    struct CSharedData
    {
        // Used as signal that shutdown is in progress from main thread to
        // speed up the queries by discarding read queries and writing to
        // the sqlite file instead of the remote mysql server.
        // The worker thread signals the main thread that all queries are
        // processed by setting this variable to false again.
        std::atomic_bool m_Shutdown{false};
        // Queries go first to the backup thread. This semaphore signals about
        // new queries.
        CSemaphore m_NumBackup;
        // When the backup thread processed the query, it signals the main
        // thread with this semaphore about the new query
        CSemaphore m_NumWorker;
 
        // spsc queue with additional backup worker to look at queries first.
        std::unique_ptr<struct CSqlExecData> m_aQueries[512];
    };
 
    std::shared_ptr<CSharedData> m_pShared;
    void *m_pWorkerThread = nullptr;
    void *m_pBackupThread = nullptr;
};
 
#endif // ENGINE_SERVER_DATABASES_CONNECTION_POOL_H