Instantiating Server (C++) Example

In distributed systems, it is common to model both servers and clients as specializations of a more generic Node abstraction. This allows us to capture shared functionality (like initialization, naming, or lifecycle management) while leaving protocol-specific or role-specific logic to subclasses.

// Example: Object-Oriented Server Abstraction in C++ for a Distributed System

class Node {
protected:
    std::string nodeName;
public:
    explicit Node(const std::string& name) : nodeName(name) {}
    virtual ~Node() = default;

    std::string getName() const { return nodeName; }
    virtual void start() = 0;   // Force subclasses to implement startup logic
    virtual void stop() = 0;    // Force subclasses to implement cleanup logic
};

// Abstract interface for services handled by servers
class IService {
public:
    virtual ~IService() = default;
    virtual void handleRequest(const std::string& request) = 0;
};

// Concrete server implementation
class A1Server : public Node {
    std::shared_ptr<IService> service;   // Service instance handled by this server
    std::string dbFilePath;              // File path for persistence (e.g., metadata, state)

public:
    explicit A1Server(const std::string& name, std::shared_ptr<IService> svc)
        : Node(name), service(std::move(svc)) {}

    void setDbFilePath(const std::string& path) { dbFilePath = path; }
    std::string getDbFilePath() const { return dbFilePath; }

    void start() override {
        // Initialize resources (socket, threads, db connections, etc.)
        std::cout << "Starting server: " << nodeName << std::endl;
        if (!dbFilePath.empty()) {
            std::cout << "Using database file: " << dbFilePath << std::endl;
        }
        // Imagine: bind socket, listen, accept connections, dispatch to service
    }

    void stop() override {
        // Graceful cleanup of resources
        std::cout << "Stopping server: " << nodeName << std::endl;
    }
};

// Example of a concrete service implementation
class EchoService : public IService {
public:
    void handleRequest(const std::string& request) override {
        std::cout << "EchoService received: " << request << std::endl;
    }
};

// Example usage
int main() {
    auto service = std::make_shared<EchoService>();
    A1Server server("DistributedNode1", service);
    server.setDbFilePath("state.db");

    server.start();
    service->handleRequest("Hello, world!");
    server.stop();
}

In practice, a real distributed server would replace the placeholder logic with:

• Socket setup: Binding to an IP and port, accepting client connections.
• Concurrency: Thread pools or async event loops to handle multiple requests in parallel.
• Persistence: Storing state in a database or replicated log for fault tolerance.
• Fault-tolerance mechanisms: Retry logic, leader election, or consensus protocols such as Raft.