📦 pubsub-lib

A lightweight, header-only C++20 Publish-Subscribe library with type-safe events, RAII-based unsubscription, and async support.

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✨ Features

• ✅ Type-safe event publishing
• ✅ Support for multiple publishers and event types
• ✅ RAII-based unsubscription via SubscriptionToken
• ✅ Subscriber lifetime management
• ✅ Async dispatching via std::async, std::execution, or oneTBB (if found)
• ✅ Header-only, C++20

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✅ Compatibility

| OS | Compiler | Generator | Status | |----------|--------------|-------------------|--------| | Ubuntu | g++, clang++ | Makefiles, Ninja | | | Windows | MSVC | Visual Studio 17 | | | macOS | clang++, g++ | Makefiles, Ninja | |

🧪 All environments verified via GitHub Actions.

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🚀 Getting Started

CMake Project Integration

bash git clone https://github.com/cpp-for-everything/pubsub-lib.git

In your CMakeLists.txt:

```cmake add_subdirectory(pubsub-lib)

targetlinklibraries(my_app PRIVATE pubsub::pubsub) ```

Or Install System-Wide

bash cmake -B build -S pubsub-lib -DCMAKE_INSTALL_PREFIX=/usr/local cmake --build build --target install

Then:

cmake find_package(pubsub REQUIRED) target_link_libraries(my_app PRIVATE pubsub::pubsub)

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📃 Usage

1. Define Events

cpp constexpr auto MyEvent = pubsub::Event<void(int)>();

Or organize events:

cpp struct MyEvents { static constexpr auto Ping = pubsub::Event<void()>(); static constexpr auto Data = pubsub::Event<void(int)>(); };

2. Create a Publisher

cpp pubsub::Publisher pub;

3. Subscribe

a) Lambda or free function

cpp pub.subscribe<MyEvents::Ping>([] { std::cout << "Ping!\n"; });

b) Member function

```cpp struct Listener { void on_data(int x) { std::cout << "Got " << x << "\n"; } } obj;

pub.subscribeMyEvents::Data(&obj, &Listener::on_data); ```

c) Lifetime-aware Subscriber class

```cpp class MySubscriber : public pubsub::Subscriber { int total = 0; public: void on_data(int x) { total += x; }

void subscribe_to(pubsub::Publisher& pub) override {
    store_token(pub.subscribe<MyEvents::Data>(this, &MySubscriber::on_data));
    Subscriber::subscribe_to(pub);
}

void unsubscribe_from(pubsub::Publisher& pub) override {
    pub.unsubscribe<MyEvents::Data>(this);
}

}; ```

4. Emit Events

a) Synchronously

cpp pub.emit<MyEvents::Data>(123);

b) Using std::async

cpp pub.emit_thread_async<MyEvents::Data>(42);

c) oneTBB (if the TBB package is found by CMake)

cpp pub.emit_tbb_async<MyEvents::Data>(42);

⚠️ Make sure oneTBB is installed and discoverable by CMake.

d) Using <execution> (C++20 Parallelism TS)

cpp pub.emit_async<MyEvents::Data>(std::execution::par_unseq, 42);

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🧕 Testing

bash cmake -B build -S . cmake --build build ctest --test-dir build

Includes: - Emission correctness - Lifetime management - Safe unsubscribing - Async delivery checks

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📊 Benchmark

Benchmarks run using Google Benchmark with simulated heavy subscribers.

See benchmark/ for setup.

🔍 Emit Time (lower is better, log scale)

| Strategy | 1 sub | 10 subs | 100 subs | 500 subs | 1000 subs | |----------------------------|-------|---------|----------|----------|-----------| | Sync | 1.1 µs | 10 µs | 99 µs | 534 µs | 954 µs | | std::async | 74 µs | 682 µs | 7.2 ms | 42.5 ms | 109 ms | | std::execution::seq | 1.3 µs | 12.6 µs | 130 µs | 721 µs | 1.03 ms | | std::execution::par | 1.3 µs | 14.1 µs | 186 µs | 772 µs | 1.65 ms | | std::execution::unseq | 1.6 µs | 14.4 µs | 158 µs | 803 µs | 1.50 ms | | std::execution::par_unseq | 1.5 µs | 12 µs | 149 µs | 837 µs | 1.73 ms | | oneTBB | 1.9 µs | 10.2 µs | 84 µs | 262 µs | 618 µs |

✅ Summary

• ⚡ Use sync emit for low subscriber counts
• ♻ Use oneTBB or par_unseq for scalable performance
• ⛑️ Avoid std::async for high fanout

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📖 Citation

If you use pubsub-lib in your research or projects, please cite the following publication:

Alex Tsvetanov and Ivan Stankov.
Modern C++ Publish/Subscribe Pattern: Design, Challenges, and Implementation.
In: Proceedings of the 60th International Scientific Conference on Information, Communication and Energy Systems and Technologies (ICEST 2025), Ohrid, North Macedonia, June 26–28, 2025.
https://github.com/cpp-for-everything/pubsub-lib

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📄 License

Apache License 2.0 — see LICENSE

All source files include:

cpp // SPDX-License-Identifier: Apache-2.0

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🤝 Contributing

Pull requests welcome! Please open an issue for large changes before starting work.

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📬 Contact

For questions or collaborations, use GitHub Discussions.