Safe Callback

A wrapper around std::function with some thread-safety guarantees.

Overview

This library was conceived to solve the problem of using callbacks in systems where objects can be destroyed while a callback is still pending or running, which can happen in multithreaded applications and will lead to a crash.

This library is header-only and does not depend on any other library, so feel free to just copy it into your project or append the include directory to your project's include path.

If you need help using this library, please do not hesitate to reach out!

• Contact me: kevin at dewald dot me

Usage

The following code briefly describes how to use the safe callback. All functions of interest to the user are presented here::

#include <kvn_safe_callback.hpp>

// Create a callback wrapper
kvn::safe_callback<int(int)> cb;

// Load a lambda function into the callback wrapper
cb.load([] (int i) -> int {
    std::cout << "Callback called with " << i << std::endl;
    return i * 2;
});

// Check if the callback is loaded
if (cb.is_loaded()) {
    std::cout << "Callback is loaded" << std::endl;
}

// Another way of checking if the callback is loaded.
if (cb) {
    std::cout << "Callback is loaded" << std::endl;
}

// Call the callback and print the result
int result = cb(42);
std::cout << "Result: " << result << std::endl;

// Unload the callback
cb.unload();

A few notes that need to be highlighted on the behavior of the safe callback:

• If the callback wrapper is not loaded, attempting to call the callback will be a no-op.
• In the cases where the callback wrapper is not loaded and the internal function returns a value, the return value will be the default value of the return type. This means that all return types need to be default constructible. If you use a non-default-constructible type, the following error message will appear during compilation: error: no matching function for call to 'YourClass::YourClass()'

License

All components within this project that have not been bundled from external creators, are licensed under the terms of the MIT Licence.