Sometimes it's necessary to run code in a background task while allowing game frames to continue to run. Although it's possible to use threading for this purpose, implementing the necessary locking becomes difficult and error prone.

Simulant instead uses Coroutines for executing long-running tasks.

Starting a Coroutine

You can run a function as a coroutine by using the cr_async method.

cr_async([]() { 
    for(int i = 0; i < 1000; ++i) {

You must yield coroutines regularly to give up control to allow a game frame to run.

Coroutines resume after late_update(). If you want to schedule a coroutine to resume after time has passed then use cr_yield_for(seconds) and the coroutine will not be resumed until seconds seconds have passed.

On very rare occasions you my be required to run code on the main thread, coroutines provide cr_run_main(func) to do that. The coroutine will be yielded and func will be called immediately and then the coroutine will resume.


cr_async will return a Promise<T> which allows you to check when the coroutine has run, and what its value was when it finished. If you want to block and await the resulting value you can use cr_await(promise). If cr_await() is called in the main thread then only idle tasks and other coroutines will run while waiting, rendering will not continue.

When waiting for a promise in the main thread, you're more likely to want to use Promise<T>::then(callback) which will trigger a callback when the promise completes. then() will also return a Promise<T> and so you can change then() statements to run a sequence of tasks.