connection_manager.h

#ifndef _CONNECTION_MANAGER_H
#define _CONNECTION_MANAGER_H
/*
 * Fledge storage service.
 *
 * Copyright (c) 2017 OSisoft, LLC
 *
 * Released under the Apache 2.0 Licence
 *
 * Author: Mark Riddoch
 */

#include <sqlite3.h>

#include <plugin_api.h>
#include <list>
#include <mutex>
#include <thread>
#include <config_category.h>

#define NO_DESCRIPTORS_PER_DB   3   // 3 deascriptors per database when using WAL mode
#define DESCRIPTOR_THRESHOLD    75  // Percentage of descriptors that can be used on database connections

class Connection;
class DiskSpaceMonitor;

class ConnectionManager {
    public:
        static ConnectionManager  *getInstance();
        void                      growPool(unsigned int);
        unsigned int              shrinkPool(unsigned int);
        Connection                *allocate();
        bool                      attachNewDb(std::string &path, std::string &alias);
        bool                      attachRequestNewDb(int newDbId, sqlite3 *dbHandle);
        bool              detachNewDb(std::string &alias);
        void                      release(Connection *);
        void              shutdown();
        void              setError(const char *, const char *, bool);
        PLUGIN_ERROR          *getError()
                      {
                        return &lastError;
                      }
        void              background();
        void              setVacuumInterval(long hours)
                      {
                        m_vacuumInterval = 60 * 60 * hours;
                      };
        bool              allowMoreDatabases();
        void              setConfiguration(ConfigCategory *category)
                      {
                          m_config = category;
                      };
        std::string       getDBConfiguration();

    protected:
        ConnectionManager();

    private:
        static ConnectionManager     *instance;
        int                  SQLExec(sqlite3 *dbHandle, const char *sqlCmd,
                            char **errMsg);
        void                 noConnectionsDiagnostic();

    protected:
        std::list<Connection *>      idle;
        std::list<Connection *>      inUse;
        std::mutex                   idleLock;
        std::mutex                   inUseLock;
        std::mutex                   errorLock;
        PLUGIN_ERROR             lastError;
        bool                 m_trace;
        bool                 m_shutdown;
        std::thread          *m_background;
        long                         m_vacuumInterval;
        unsigned int             m_descriptorLimit;
        unsigned int             m_attachedDatabases;
        DiskSpaceMonitor         *m_diskSpaceMonitor;
        ConfigCategory           *m_config;
};

#endif