eventpp is a C++ event library for callbacks, event dispatcher, and event queue. With eventpp you can easily implement signal and slot mechanism, publisher and subscriber pattern, or observer pattern.
eventpp is mature and production-ready.

Facts and features

Powerful
- Supports synchronous event dispatching and asynchronous event queue.
- Configurable and extensible with policies and mixins.
- Supports event filter via mixins.
Robust
- Supports nested event. During the process of handling an event, a listener can safely dispatch event and append/prepend/insert/remove other listeners.
- Thread safety. Supports multi-threading.
- Exception safety. Most operations guarantee strong exception safety.
- Well tested. Backed by unit tests.
Fast
- The EventQueue can process 10M events in 1 second (10K events per millisecond).
- The CallbackList can invoke 100M callbacks in 1 second (100K callbacks per millisecond).
- The CallbackList can add/remove 5M callbacks in 1 second (5K callbacks per millisecond).
- With the helper class AnyData, it's possible to avoid heap allocation when sending events via EventQueue.
Flexible and easy to use
- Listeners and events can be of any type and do not need to be inherited from any base class.
- Utilities that can ease the usage, such as auto disconnecting, one shot listener, argument type adapter, etc.
- Header only, no source file, no need to build. Does not depend on other libraries.
- Only requires C++ 11.
- Written in portable and standard C++, no hacks or quirks.

License

Apache License, Version 2.0

Version 0.1.3

The master branch is usable and stable.
Don't worry about the large time span between commits and releases. The library is actively maintained.
The master branch is currently fully back compatible with the first version. So your project won't get any back compatible issues.
If you find any back compatible issue which is not announced, please report a bug.

Source code

https://github.com/wqking/eventpp

Supported compilers

Tested with MSVC 2022 and 2019, MinGW (Msys) GCC 7.2, Ubuntu GCC 5.4, Intel C++ 2022, and MacOS GCC. GCC 4.8.3 can compile the library, but I don't support or maintain for GCC prior to GCC 5. In brief, MSVC, GCC, Clang that has well support for C++11, or released after 2019, should be able to compile the library.

C++ standard requirements

To Use the library
- The library: C++11.
To develop the library
- Unit tests: C++17.
- Tutorials: C++11.
- Benchmarks: C++11.

Quick start

Namespace

eventpp

Use eventpp in your project

eventpp package is available in C++ package managers Vcpkg, Conan, and Hunter. There are various methods to use eventpp.
Please read the document for details.

Using CallbackList

#include "eventpp/callbacklist.h"
eventpp::CallbackList<void (const std::string &, const bool)> callbackList;
callbackList.append([](const std::string & s, const bool b) {
    std::cout << std::boolalpha << "Got callback 1, s is " << s << " b is " << b << std::endl;
});
callbackList.append([](std::string s, int b) {
    std::cout << std::boolalpha << "Got callback 2, s is " << s << " b is " << b << std::endl;
});
callbackList("Hello world", true);

Using EventDispatcher

#include "eventpp/eventdispatcher.h"
eventpp::EventDispatcher<int, void ()> dispatcher;
dispatcher.appendListener(3, []() {
    std::cout << "Got event 3." << std::endl;
});
dispatcher.appendListener(5, []() {
    std::cout << "Got event 5." << std::endl;
});
dispatcher.appendListener(5, []() {
    std::cout << "Got another event 5." << std::endl;
});
// dispatch event 3
dispatcher.dispatch(3);
// dispatch event 5
dispatcher.dispatch(5);

Using EventQueue

#include "eventpp/eventqueue.h"
eventpp::EventQueue<int, void (const std::string &, const bool)> queue;

queue.appendListener(3, [](const std::string s, bool b) {
    std::cout << std::boolalpha << "Got event 3, s is " << s << " b is " << b << std::endl;
});
queue.appendListener(5, [](const std::string s, bool b) {
    std::cout << std::boolalpha << "Got event 5, s is " << s << " b is " << b << std::endl;
});

// The listeners are not triggered during enqueue.
queue.enqueue(3, "Hello", true);
queue.enqueue(5, "World", false);

// Process the event queue, dispatch all queued events.
queue.process();

Documentations

Setup
- Install and use eventpp in your project
Core classes and functions
Utilities
Miscellaneous
Tips and tricks
- Samples for typical use cases
- Use C++ data type as event identifier
Heterogeneous classes and functions, for proof of concept, usually you don't need them
Translated documents
- Chinese version 中文版, thanks @marsCatXdu for the translation.

Motivations

I (wqking) am a big fan of observer pattern (publish/subscribe pattern), and I used this pattern extensively in my code. I either used GCallbackList in my cpgf library which is too simple and unsafe (not support multi-threading or nested events), or repeated coding event dispatching mechanism such as I did in my Gincu game engine (the latest version has be rewritten to use eventpp). Both methods are not fun nor robust.
Thanking to C++11, now it's quite easy to write a reusable event library with beautiful syntax (it's a nightmare to simulate the variadic template in C++03), so here is eventpp.

Change log

Version 0.1.3 Sep 21, 2023
Added utility class AnyData.
Small bugs fixes and improvements.

Version 0.1.2 Mar 11, 2022
Bug fix.
Added more unit tests.
Added utilities argumentAdapter and conditionalFunctor.
Added utilities AnyId.
Added event maker macros.

Version 0.1.1 Dec 13, 2019
Added HeterCallbackList, HeterEventDispatcher, and HeterEventQueue.

Version 0.1.0 Sep 1, 2018
First version.
Added CallbackList, EventDispatcher, EventQueue, CounterRemover, ConditionalRemover, ScopedRemover, and utilities.

Contributors

wqking	rotolof	OlivierLDff	devbharat	mpiccolino-tealblue	bazfp	Martinii89
ludekvodicka	Volatus	wallel	mangrooveforest	haberturdeur	shellinspector	bd1es
qgyhd1234	frostius	gelijian	MH2033	zhllxt	marsCatXdu	Chaojimengnan
henaiguo	sr-tream	Drise13	iamzone	RazielXYZ

I (wqking) would like to sincerely thank all participants for the contributions. Your contributions make eventpp better and bright future. I maintain the contributors list manually, according to the criteria below,

Your Pull Request is approved and merged to any branch.
Or there is commit or work related to your reported issue. That's to say, the bug you reported is fixed, or the advice you suggested is adopted.

If you think you should be on the contributors list, such as I miss out your work, or you have work not technology related but can help eventpp growing (such as posting review in social network with large amount of readers), please contact me, I'm happy to get the contributors list larger.