namespace mongo {/*** This is the entrypoint from the transport layer into mongod or mongos.** The ServiceEntryPoint accepts new Sessions from the TransportLayer, and is* responsible for running these Sessions in a get-Message, run-Message,* reply-with-Message loop.  It may not do this on the TransportLayer’s thread.*/
/*** 这是从transport layer到mongod或者mongos的入口点。** ServiceEntryPoint从TransportLayer中接收新的Session，并且负责运行这些Sessions的* get-Message，run-Message和reply-with-Message生命周期。它可能不会在TransportLayer的线程* 中这些事情。*/
class ServiceEntryPoint {MONGO_DISALLOW_COPYING(ServiceEntryPoint);public:virtual ~ServiceEntryPoint() = default;/*** Begin running a new Session. This method returns immediately.*//*** 开始一个新的Session。这个方法会马上返回。*/virtual void startSession(transport::SessionHandle session) = 0;/*** End all sessions that do not match the mask in tags.*//*** 结束所有和tags中掩码不匹配的sessions。*/virtual void endAllSessions(transport::Session::TagMask tags) = 0;/*** Starts the service entry point*//*** 启动服务入口点。*/virtual Status start() = 0;/*** Shuts down the service entry point.*//*** 关闭服务入口点。*/virtual bool shutdown(Milliseconds timeout) = 0;/*** Append high-level stats to a BSONObjBuilder for serverStatus*//*** 为serverStatus向BSONObjBuilder追加高级状态。*/virtual void appendStats(BSONObjBuilder* bob) const = 0;/*** Returns the number of sessions currently open.*//*** 返回当前打开的sessions数量。*/virtual size_t numOpenSessions() const = 0;/*** Processes a request and fills out a DbResponse.*//*** 处理一个请求并写入DbResponse。* P. S. 敲黑板了， 同志们，这里就是处理请求的地方了啊！*/virtual DbResponse handleRequest(OperationContext* opCtx, const Message& request) = 0;protected:ServiceEntryPoint() = default;
};}  // namespace mongo

namespace mongo {
class ServiceContext;namespace transport {
class Session;
}  // namespace transport/*** A basic entry point from the TransportLayer into a server.** The server logic is implemented inside of handleRequest() by a subclass.* startSession() spawns and detaches a new thread for each incoming connection* (transport::Session).*/
/*** 从TransportLayer到server的一个基本入口点。** 服务器处理请求的逻辑是通过子类的handleRequest()方法实现的。* startSession()会spawns并且分配一个新的线程来处理每个到来的连接（transport:Session）* spawn: （鱼、蛙等）大量产（卵）;引起，酿成**/
class ServiceEntryPointImpl : public ServiceEntryPoint {MONGO_DISALLOW_COPYING(ServiceEntryPointImpl);public:// 构造函数explicit ServiceEntryPointImpl(ServiceContext* svcCtx);void startSession(transport::SessionHandle session) override;void endAllSessions(transport::Session::TagMask tags) final;Status start() final;bool shutdown(Milliseconds timeout) final;void appendStats(BSONObjBuilder* bob) const final;size_t numOpenSessions() const final {return _currentConnections.load();}private:using SSMList = stdx::list<std::shared_ptr<ServiceStateMachine>>;using SSMListIterator = SSMList::iterator;ServiceContext* const _svcCtx;AtomicWord<std::size_t> _nWorkers;mutable stdx::mutex _sessionsMutex;stdx::condition_variable _shutdownCondition;SSMList _sessions;size_t _maxNumConnections{DEFAULT_MAX_CONN};AtomicWord<size_t> _currentConnections{0};AtomicWord<size_t> _createdConnections{0};std::unique_ptr<transport::ServiceExecutorReserved> _adminInternalPool;
};/** Returns true if a session with remote/local addresses should be exempted from maxConns*/
/** 如果远程或本地的session可以从最大连接数约束中豁免则返回true*/
bool shouldOverrideMaxConns(const transport::SessionHandle& session,const std::vector<stdx::variant<CIDR, std::string>>& exemptions);}  // namespace mongo