event_bus_example.cpp

Demonstrates thread-safe pub/sub messaging with simple_event_bus.

Demonstrates thread-safe pub/sub messaging with simple_event_bus.Shows event publishing, subscription, unsubscription, priority ordering, and error callbacks.

See also

kcenon::common::simple_event_bus

// BSD 3-Clause License
// Copyright (c) 2021-2025, 🍀☀🌕🌥 🌊
// See the LICENSE file in the project root for full license information.
 
 
#include <kcenon/common/patterns/event_bus.h>
 
#include <iostream>
#include <string>
 
using namespace kcenon::common;
 
// Custom event types
struct user_logged_in
{
    std::string username;
    std::string ip_address;
};
 
struct order_placed
{
    int order_id;
    double total;
};
 
struct system_alert
{
    std::string message;
    int severity;
};
 
int main()
{
    std::cout << "=== Event Bus Example ===\n\n";
 
    auto& bus = get_event_bus();
 
    // Subscribe to user login events
    std::cout << "1. Subscribing to events...\n";
    auto login_sub = bus.subscribe<user_logged_in>(
        [](const user_logged_in& e)
        { std::cout << "   [Auth] User '" << e.username << "' logged in from " << e.ip_address << "\n"; });
 
    auto audit_sub = bus.subscribe<user_logged_in>(
        [](const user_logged_in& e)
        { std::cout << "   [Audit] Login recorded for '" << e.username << "'\n"; });
 
    // Subscribe to order events
    auto order_sub = bus.subscribe<order_placed>(
        [](const order_placed& e)
        { std::cout << "   [Orders] Order #" << e.order_id << " placed, total: $" << e.total << "\n"; });
 
    // Set error callback
    bus.set_error_callback([](const std::string& error, size_t, uint64_t)
                           { std::cerr << "   [Error] Event bus error: " << error << "\n"; });
 
    // Publish events
    std::cout << "\n2. Publishing events...\n";
    bus.publish(user_logged_in{"alice", "192.168.1.100"});
    bus.publish(order_placed{1001, 59.99});
 
    // Unsubscribe audit logger
    std::cout << "\n3. Unsubscribing audit logger...\n";
    bus.unsubscribe(audit_sub);
 
    // Publish again — only auth handler receives
    std::cout << "\n4. Publishing after unsubscribe...\n";
    bus.publish(user_logged_in{"bob", "10.0.0.1"});
 
    // Priority ordering
    std::cout << "\n5. Priority-ordered publishing...\n";
    auto alert_sub = bus.subscribe<system_alert>(
        [](const system_alert& e)
        { std::cout << "   [Alert] severity=" << e.severity << ": " << e.message << "\n"; });
 
    bus.publish(system_alert{"CPU usage high", 2}, event_priority::high);
    bus.publish(system_alert{"Disk space low", 1}, event_priority::normal);
 
    // Cleanup
    bus.unsubscribe(login_sub);
    bus.unsubscribe(order_sub);
    bus.unsubscribe(alert_sub);
 
    std::cout << "\nDone.\n";
    return 0;
}