added a simple message bus

include/matador/utils/message_bus.hpp

@@ -0,0 +1,222 @@
+#ifndef MATADOR_MESSAGE_BUS_HPP
+#define MATADOR_MESSAGE_BUS_HPP
+
+#include <atomic>
+#include <functional>
+#include <memory>
+#include <mutex>
+#include <shared_mutex>
+#include <typeindex>
+#include <typeinfo>
+#include <unordered_map>
+#include <vector>
+#include <algorithm>
+#include <stdexcept>
+
+namespace matador::utils {
+class message_bus; // forward
+
+class message {
+public:
+    message();
+
+    // Owning: copy into an owned shared_ptr (may allocate)
+    template<typename T>
+    explicit message(const T& value) {
+        auto strong = std::make_shared<T>(value);               // allocate
+        owner_ = std::static_pointer_cast<void>(strong);       // share ownership as void*
+        ptr_ = static_cast<const void*>(strong.get());
+        type_ = std::type_index(typeid(T));
+    }
+
+    // Non-owning: zero-copy reference to an existing object (no allocation)
+    // Caller must guarantee lifetime of `ref` for the usage duration.
+    template<typename T>
+    static message from_ref(const T& ref) {
+        message m;
+        m.ptr_ = static_cast<const void*>(std::addressof(ref));
+        m.type_ = std::type_index(typeid(T));
+        // owner_ remains null => non-owning
+        return m;
+    }
+
+    // Owning from shared_ptr (no extra copy; shares ownership)
+    template<typename T>
+    static message from_shared(std::shared_ptr<T> sp) {
+        message m;
+        m.owner_ = std::static_pointer_cast<void>(sp);
+        m.ptr_ = static_cast<const void*>(sp.get());
+        m.type_ = std::type_index(typeid(T));
+        return m;
+    }
+
+    [[nodiscard]] bool empty() const;
+    [[nodiscard]] std::type_index type() const;
+
+    template<typename T>
+    [[nodiscard]] bool is() const { return type_ == std::type_index(typeid(T)); }
+
+    // Access as typed reference. Works for both owning and non-owning.
+    // Throws std::bad_cast if type mismatch.
+    template<typename T>
+    const T& get() const {
+        if (!is<T>()) throw std::bad_cast();
+        const void* p = msg_ptr();
+        if (!p) throw std::runtime_error("AnyMessage: empty pointer");
+        return *static_cast<const T*>(p);
+    }
+
+    // Return the raw const void* pointer to the stored object (may be non-owning)
+    [[nodiscard]] const void* msg_ptr() const;
+
+private:
+    const void* ptr_;                 // non-owning raw pointer (if set)
+    std::shared_ptr<void> owner_;     // owning pointer if we made a copy or got shared_ptr
+    std::type_index type_{typeid(void)};
+};
+
+// Forward declare Subscription so MessageBus can return it.
+class subscription {
+public:
+    subscription() = default;
+    subscription(message_bus* bus, std::type_index type, uint64_t id);
+
+    // Move-only (non-copyable)
+    subscription(const subscription&) = delete;
+    subscription& operator=(const subscription&) = delete;
+    subscription(subscription&& other) noexcept;
+    subscription& operator=(subscription&& other) noexcept;
+
+    ~subscription();
+
+    void unsubscribe();
+
+    [[nodiscard]] bool valid() const;
+
+private:
+    message_bus* bus_ = nullptr;
+    std::type_index type_{typeid(void)};
+    uint64_t id_ = 0;
+};
+
+// === MessageBus: runtime-registered, thread-safe ===
+class message_bus {
+public:
+    using HandlerId = uint64_t;
+
+    message_bus() : next_id_{1} {}
+
+    // Subscribe with a free function or lambda
+    template<typename T>
+    subscription subscribe(std::function<void(const T&)> handler,
+                           std::function<bool(const T&)> filter = nullptr)
+    {
+        auto id = next_id_.fetch_add(1, std::memory_order_relaxed);
+        std::unique_lock writeLock(mutex_);
+
+        auto &vec = handlers_[std::type_index(typeid(T))];
+        Entry e;
+        e.id = id;
+        e.handler = [h = std::move(handler)](const void* p) {
+            h(*static_cast<const T*>(p));
+        };
+        if (filter) {
+            e.filter = [f = std::move(filter)](const void* p) -> bool {
+                return f(*static_cast<const T*>(p));
+            };
+        } else {
+            e.filter = nullptr;
+        }
+        vec.emplace_back(std::move(e));
+        return {this, std::type_index(typeid(T)), id};
+    }
+
+    // Subscribe raw pointer instance; caller ensures lifetime
+    template<typename T, typename C>
+    subscription subscribe(C* instance, void (C::*memberFn)(const T&),
+                           std::function<bool(const T&)> filter = nullptr)
+    {
+        auto fn = [instance, memberFn](const T& m) { (instance->*memberFn)(m); };
+        return subscribe<T>(std::function<void(const T&)>(fn), std::move(filter));
+    }
+
+    // Subscribe shared_ptr instance (safe)
+    template<typename T, typename C>
+    subscription subscribe(std::shared_ptr<C> instance, void (C::*memberFn)(const T&),
+                           std::function<bool(const T&)> filter = nullptr)
+    {
+        std::weak_ptr<C> w = instance;
+        auto handler = [w, memberFn](const T& m) {
+            if (auto s = w.lock()) {
+                (s.get()->*memberFn)(m);
+            }
+        };
+
+        std::function<bool(const T&)> filt = nullptr;
+        if (filter) {
+            filt = [w, filter = std::move(filter)](const T& m) -> bool {
+                if (w.expired()) {
+                    return false;
+                }
+                return filter(m);
+            };
+        }
+        return subscribe<T>(std::move(handler), std::move(filt));
+    }
+
+    // Unsubscribe by type-specific id (RAII calls this)
+    template<typename T>
+    void unsubscribe(const HandlerId id) {
+        unsubscribe(std::type_index(typeid(T)), id);
+    }
+
+    // Unsubscribe by explicit type_index and id
+    void unsubscribe(std::type_index type, HandlerId id);
+
+    // Unsubscribe by id regardless of type (O(#types) scan)
+    void unsubscribe(HandlerId id);
+
+    // Publish a typed message (fast)
+    template<typename T>
+    void publish(const T& msg) const {
+        std::vector<Entry> snapshot;
+        {
+            std::shared_lock readLock(mutex_);
+            const auto it = handlers_.find(std::type_index(typeid(T)));
+            if (it == handlers_.end()) {
+                return;
+            }
+            snapshot = it->second; // copy list to avoid holding lock during callbacks
+        }
+        for (const auto &e : snapshot) {
+            if (!e.filter || e.filter(&msg)) e.handler(&msg);
+        }
+    }
+
+    // Publish using AnyMessage (zero-copy if AnyMessage is non-owning)
+    void publish(const message& msg) const;
+
+private:
+    friend class subscription;
+
+    struct Entry {
+        HandlerId id;
+        std::function<void(const void*)> handler;
+        std::function<bool(const void*)> filter;
+    };
+
+    mutable std::shared_mutex mutex_;
+    std::unordered_map<std::type_index, std::vector<Entry>> handlers_;
+    std::atomic<HandlerId> next_id_;
+};
+
+// RAII unsubscribe implementation
+inline void subscription::unsubscribe() {
+    if (bus_) {
+        bus_->unsubscribe(type_, id_);
+        bus_ = nullptr;
+    }
+}
+}
+
+#endif //MATADOR_MESSAGE_BUS_HPP

source/core/CMakeLists.txt

@@ -13,8 +13,8 @@ add_library(matador-core STATIC
   ../../include/matador/net/reactor.hpp
   ../../include/matador/net/select_fd_sets.hpp
   ../../include/matador/net/socket_interrupter.hpp
-  ../../include/matador/object/attribute_definition_generator.hpp
   ../../include/matador/object/attribute_definition.hpp
+  ../../include/matador/object/attribute_definition_generator.hpp
   ../../include/matador/object/basic_object_info.hpp
   ../../include/matador/object/error_code.hpp
   ../../include/matador/object/foreign_node_completer.hpp
@@ -30,6 +30,7 @@ add_library(matador-core STATIC
   ../../include/matador/object/schema.hpp
   ../../include/matador/object/schema_node.hpp
   ../../include/matador/object/schema_node_iterator.hpp
+  ../../include/matador/sql/statement_cache.hpp
   ../../include/matador/utils/access.hpp
   ../../include/matador/utils/attribute_reader.hpp
   ../../include/matador/utils/attribute_writer.hpp
@@ -47,13 +48,14 @@ add_library(matador-core STATIC
   ../../include/matador/utils/errors.hpp
   ../../include/matador/utils/export.hpp
   ../../include/matador/utils/fetch_type.hpp
-  ../../include/matador/utils/file.hpp
   ../../include/matador/utils/field_attributes.hpp
+  ../../include/matador/utils/file.hpp
   ../../include/matador/utils/foreign_attributes.hpp
   ../../include/matador/utils/identifier.hpp
   ../../include/matador/utils/leader_follower_thread_pool.hpp
   ../../include/matador/utils/library.hpp
   ../../include/matador/utils/macro_map.hpp
+  ../../include/matador/utils/message_bus.hpp
   ../../include/matador/utils/os.hpp
   ../../include/matador/utils/placeholder.hpp
   ../../include/matador/utils/primary_key_attribute.hpp
@@ -73,8 +75,8 @@ add_library(matador-core STATIC
   logger/log_manager.cpp
   logger/logger.cpp
   logger/rotating_file_sink.cpp
-  object/attribute_definition_generator.cpp
   object/attribute_definition.cpp
+  object/attribute_definition_generator.cpp
   object/basic_object_info.cpp
   object/error_code.cpp
   object/foreign_node_completer.cpp
@@ -93,6 +95,7 @@ add_library(matador-core STATIC
   utils/identifier.cpp
   utils/leader_follower_thread_pool.cpp
   utils/library.cpp
+  utils/message_bus.cpp
   utils/os.cpp
   utils/primary_key_attribute.cpp
   utils/string.cpp
@@ -101,7 +104,6 @@ add_library(matador-core STATIC
   utils/uuid.cpp
   utils/value.cpp
   utils/version.cpp
-        ../../include/matador/sql/statement_cache.hpp
 )
 
 target_link_libraries(matador-core ${CMAKE_DL_LIBS})

source/core/utils/message_bus.cpp

@@ -0,0 +1,97 @@
+#include "matador/utils/message_bus.hpp"
+
+namespace matador::utils {
+message::message()
+: ptr_(nullptr)
+, owner_(nullptr)
+, type_(typeid(void)) {}
+
+bool message::empty() const {
+  return ptr_ == nullptr && !owner_;
+}
+
+std::type_index message::type() const {
+  return type_;
+}
+
+const void * message::msg_ptr() const {
+  return owner_ ? owner_.get() : ptr_;
+}
+
+subscription::subscription(message_bus *bus, const std::type_index type, const uint64_t id)
+: bus_(bus)
+, type_(type)
+, id_(id) {}
+
+subscription::subscription(subscription &&other) noexcept
+: bus_(other.bus_)
+, type_(other.type_)
+, id_(other.id_) {
+  other.bus_ = nullptr;
+}
+
+subscription& subscription::operator=(subscription &&other) noexcept {
+  if (this != &other) {
+    unsubscribe();
+    bus_ = other.bus_;
+    type_ = other.type_;
+    id_ = other.id_;
+    other.bus_ = nullptr;
+  }
+  return *this;
+}
+
+subscription::~subscription() {
+  unsubscribe();
+}
+
+bool subscription::valid() const {
+  return bus_ != nullptr;
+}
+
+void message_bus::unsubscribe(const std::type_index type, HandlerId id) {
+  std::unique_lock writeLock(mutex_);
+  const auto it = handlers_.find(type);
+  if (it == handlers_.end()) {
+    return;
+  }
+  auto &handler_vector = it->second;
+  handler_vector.erase(std::remove_if(handler_vector.begin(), handler_vector.end(),
+                           [id](const Entry &e) { return e.id == id; }),
+            handler_vector.end());
+  if (handler_vector.empty()) {
+    handlers_.erase(it);
+  }
+}
+
+void message_bus::unsubscribe(HandlerId id) {
+  std::unique_lock writeLock(mutex_);
+  for (auto it = handlers_.begin(); it != handlers_.end(); ) {
+    auto &handler_vector = it->second;
+    handler_vector.erase(std::remove_if(handler_vector.begin(), handler_vector.end(),
+                             [id](const Entry &e) { return e.id == id; }),
+              handler_vector.end());
+    if (handler_vector.empty()) it = handlers_.erase(it);
+    else ++it;
+  }
+}
+
+void message_bus::publish(const message &msg) const {
+  if (msg.empty()) {
+    return;
+  }
+  std::vector<Entry> snapshot;
+  {
+    std::shared_lock readLock(mutex_);
+    const auto it = handlers_.find(msg.type());
+    if (it == handlers_.end()) {
+      return;
+    }
+    snapshot = it->second;
+  }
+  const void* p = msg.msg_ptr();
+  for (const auto &e : snapshot) {
+    if (!e.filter || e.filter(p)) e.handler(p);
+  }
+}
+}

test/core/CMakeLists.txt

@@ -17,6 +17,7 @@ add_executable(CoreTests
   object/AttributeDefinitionGeneratorTest.cpp
   object/PrimaryKeyResolverTest.cpp
   object/SchemaTest.cpp
+  utils/MessageBusTest.cpp
 )
 
 target_link_libraries(CoreTests matador-core Catch2::Catch2WithMain)

test/core/utils/MessageBusTest.cpp

@@ -0,0 +1,157 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include "matador/utils/message_bus.hpp"
+
+#include <thread>
+
+struct TestEvent { int value; };
+struct FilterEvent { int value; };
+struct ClassEvent { std::string msg; };
+
+class Receiver {
+public:
+    void on_event(const ClassEvent& e) {
+        received.push_back(e.msg);
+    }
+    std::vector<std::string> received;
+};
+
+using namespace matador::utils;
+
+TEST_CASE("Basic publish/subscribe works", "[MessageBus]") {
+    message_bus bus;
+    int counter = 0;
+
+    auto sub = bus.subscribe<TestEvent>([&](const TestEvent& e) {
+        counter += e.value;
+    });
+
+    bus.publish(TestEvent{1});
+    bus.publish(TestEvent{2});
+
+    REQUIRE(counter == 3);
+}
+
+TEST_CASE("Filtering works", "[MessageBus]") {
+    message_bus bus;
+    int counter = 0;
+
+    auto sub = bus.subscribe<FilterEvent>(
+        [&](const FilterEvent& e) { counter += e.value; },
+        [](const FilterEvent& e) { return e.value % 2 == 0; } // only even
+    );
+
+    bus.publish(FilterEvent{1}); // should be filtered out
+    bus.publish(FilterEvent{2});
+    bus.publish(FilterEvent{3}); // filtered
+    bus.publish(FilterEvent{4});
+
+    REQUIRE(counter == 6); // only 2 + 4
+}
+
+TEST_CASE("Member function subscription works", "[MessageBus]") {
+    message_bus bus;
+    Receiver r;
+
+    auto sub = bus.subscribe<ClassEvent>(&r, &Receiver::on_event);
+    bus.publish(ClassEvent{"hello"});
+    bus.publish(ClassEvent{"world"});
+
+    REQUIRE(r.received.size() == 2);
+    REQUIRE(r.received[0] == "hello");
+    REQUIRE(r.received[1] == "world");
+}
+
+TEST_CASE("Shared_ptr instance subscription works", "[MessageBus]") {
+    message_bus bus;
+    const auto r = std::make_shared<Receiver>();
+
+    auto sub = bus.subscribe<ClassEvent>(r, &Receiver::on_event);
+    bus.publish(ClassEvent{"foo"});
+
+    REQUIRE(r->received.size() == 1);
+    REQUIRE(r->received[0] == "foo");
+}
+
+TEST_CASE("RAII unsubscription works", "[MessageBus]") {
+    message_bus bus;
+    int counter = 0;
+
+    {
+        auto sub = bus.subscribe<TestEvent>([&](const TestEvent& e) {
+            counter += e.value;
+        });
+        bus.publish(TestEvent{5});
+        REQUIRE(counter == 5);
+    }
+
+    // sub goes out of scope, unsubscribed
+    bus.publish(TestEvent{5});
+    REQUIRE(counter == 5);
+}
+
+TEST_CASE("Type-erased AnyMessage publish works", "[MessageBus]") {
+    message_bus bus;
+    int counter = 0;
+
+    auto sub = bus.subscribe<TestEvent>([&](const TestEvent& e) {
+        counter += e.value;
+    });
+
+    const message msg(TestEvent{10});
+    bus.publish(msg);
+
+    REQUIRE(counter == 10);
+}
+
+TEST_CASE("Multiple subscribers all receive messages", "[MessageBus]") {
+    message_bus bus;
+    int a = 0, b = 0;
+
+    auto sub1 = bus.subscribe<TestEvent>([&](const TestEvent& e) { a += e.value; });
+    auto sub2 = bus.subscribe<TestEvent>([&](const TestEvent& e) { b += e.value; });
+
+    bus.publish(TestEvent{3});
+    REQUIRE(a == 3);
+    REQUIRE(b == 3);
+}
+
+TEST_CASE("Stress test with multi-threaded publish and subscribe", "[MessageBus][stress]") {
+    message_bus bus;
+    std::atomic<int> counter{0};
+    constexpr int numThreads = 8;
+    constexpr int eventsPerThread = 5000;
+
+    // Subscribe before launching publishers
+    auto sub = bus.subscribe<TestEvent>([&](const TestEvent& e) {
+        counter.fetch_add(e.value, std::memory_order_relaxed);
+    });
+
+    std::vector<std::thread> threads;
+    threads.reserve(numThreads);
+
+    // Publisher threads
+    for (int t = 0; t < numThreads; ++t) {
+        threads.emplace_back([&] {
+            for (int i = 0; i < eventsPerThread; ++i) {
+                bus.publish(TestEvent{1});
+            }
+        });
+    }
+
+    // Concurrent subscriber thread
+    threads.emplace_back([&] {
+        for (int i = 0; i < 1000; ++i) {
+            auto tempSub = bus.subscribe<TestEvent>([&](const TestEvent& e) {
+                counter.fetch_add(e.value, std::memory_order_relaxed);
+            });
+            std::this_thread::yield(); // simulate churn
+        }
+    });
+
+    for (auto& th : threads) {
+        th.join();
+    }
+
+    REQUIRE(counter.load(std::memory_order_relaxed) >= numThreads * eventsPerThread);
+}