// mongo的命名空间

namespace mongo {

class OperationContext;

// transport的命名空间, 我是cpp小白, 命名空间还可以嵌套, TODO:namespace学习一下

namespace transport {

// 连接的SSL模型, TODO:SSL可以了解一下哦

enum ConnectSSLMode { kGlobalSSLMode, kEnableSSL, kDisableSSL };

// 这个应该声明的意思, TODO:C++声明类

class Reactor;

// using还可以这么用, shared_ptr是啥, 可以了解一下

// 妈的, 写不下去了, 就我这这样的还来看mongo的C++源码

using ReactorHandle = std::shared_ptr<Reactor>;

/**

 * The TransportLayer moves Messages between transport::Endpoints and the database.

 * This class owns an Acceptor that generates new endpoints from which it can

 * source Messages.

 *

 * The TransportLayer creates Session objects and maps them internally to

 * endpoints. New Sessions are passed to the database (via a ServiceEntryPoint)

 * to be run. The database must then call additional methods on the TransportLayer

 * to manage the Session in a get-Message, handle-Message, return-Message cycle.

 * It must do this on its own thread(s).

 *

 * References to the TransportLayer should be stored on service context objects.

 */

/**

 * TransportLayer在transport::Endpoints和database(也就是mongo了)之间传递消息(message)。

 * 这个类有一个Acceptor, 这个Acceptor可以从原始的message中生成一个新的endpoints。

 *

 * TransportLay创建新的Session对象，并且在内部将它们映射到endpoints。新的Session通过一个ServiceEntryPoint

 * 传递到database来运行的。database后面必须调用TransportLay的其他方法来管理get-Message,

 * handle-Message和return-Message周期中的Session。而且必须在它自己的线程中做这些事。

 */

class TransportLayer {

    // 这是个什么鬼

    MONGO_DISALLOW_COPYING(TransportLayer);

public:

    // 声明各种状态

    static const Status SessionUnknownStatus;

    static const Status ShutdownStatus;

    static const Status TicketSessionUnknownStatus;

    static const Status TicketSessionClosedStatus;

    // 把Session对象设为友元

    friend class Session;

    // virtual, TODO:虚方法了解一下

    virtual ~TransportLayer() = default;

    // 连接

    virtual StatusWith<SessionHandle> connect(HostAndPort peer,

                                              ConnectSSLMode sslMode,

                                              Milliseconds timeout) = ;

    // 异步连接

    virtual Future<SessionHandle> asyncConnect(HostAndPort peer,

                                               ConnectSSLMode sslMode,

                                               const ReactorHandle& reactor,

                                               Milliseconds timeout) = ;

    /**

     * Start the TransportLayer. After this point, the TransportLayer will begin accepting active

     * sessions from new transport::Endpoints.

     */

    /**

     * 启动TransportLayer。在这之后，TransportLayer将开始从新的transport::Endpoints接收活跃的session。

     */

    virtual Status start() = ;

    /**

     * Shut the TransportLayer down. After this point, the TransportLayer will

     * end all active sessions and won't accept new transport::Endpoints. Any

     * future calls to wait() or asyncWait() will fail. This method is synchronous and

     * will not return until all sessions have ended and any network connections have been

     * closed.

     */

    /**

     * 关闭TransportLay。在这之后，TransportLayer将终止所有活跃的sessions并且不再接收新的EndPoints。

     * 任何将来对wait()和asyncWait()的调用都会失败。这个方法是同步的，并且直到所有的sessions都结束了

     * 之后并且任何网络连接都关闭了才会返回。

     */

    virtual void shutdown() = ;

    /**

     * Optional method for subclasses to setup their state before being ready to accept

     * connections.

     */

    /**

     * 这个是可选的方法，子类可以用这个方法在准备接收连接的时候去设置它们的状态。

     */

    virtual Status setup() = ;

    enum WhichReactor { kIngress, kEgress, kNewReactor };

    virtual ReactorHandle getReactor(WhichReactor which) = ;

    virtual BatonHandle makeBaton(OperationContext* opCtx) {

        return nullptr;

    }

protected:

    TransportLayer() = default;

};

}  // namespace transport

}  // namespace mongo