📦 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

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

In your CMakeLists.txt:

add_subdirectory(pubsub-lib)

target_link_libraries(my_app PRIVATE pubsub::pubsub)

Or Install System-Wide

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

Then:

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

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📃 Usage

1. Define Events

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

Or organize events:

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

2. Create a Publisher

pubsub::Publisher pub;

3. Subscribe

a) Lambda or free function

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

b) Member function

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

pub.subscribe<MyEvents::Data>(&obj, &Listener::on_data);

c) Lifetime-aware Subscriber class

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

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

b) Using std::async

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

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

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

⚠️ Make sure oneTBB is installed and discoverable by CMake.

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

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

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🧕 Testing

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:

// 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.