IExecutor

IExecutor is an abstraction around some concrete event loop. The library code uses IExecutor to "post" callbacks and to start timers.

An application using SSP21-CPP needs to provide a concrete implementation of this abstract class. The most common event-based networking library in C++ is ASIO. As such, the exe4cpp dependency provides two concrete implementations of IExecutor based on ASIO:

• BasicExecutor is a single-threaded implementation.
• StrandExecutor is multi-threaded and meant to be used with a ThreadPool. It can be forked to create sibling executors which guarantee that any callback (e.g. a timer) are only called by a single thread at a time.

Note

While SSP21-CPP only provides examples of integration with ASIO, it should be quite possible to adapt other event libraries such as libuv to the abstractions that SSP21-CPP provides.

Event-driven

Ultimately, any application using the library will need to run an event loop. The proxy application uses the BasicExecutor to run a single-threaded event loop:

const auto executor = make_shared<exe4cpp::BasicExecutor>(std::make_shared<asio::io_service>());

// omitted: configure proxy components

SIMPLE_LOG_BLOCK(logger, ssp21::levels::event, "begin io_context::run()");
executor->get_service()->run();
SIMPLE_LOG_BLOCK(logger, ssp21::levels::event, "end io_context::run()");

The program exits after the last 3 lines above. The program consists solely of asynchronous operations, and is capable of running many concurrent communication sessions without blocking.