Performance

Each time a coroutine is created (when it is first called) a coroutine frame is allocated to hold the coroutine state. The frame can be allocated on the heap, or on the stack in some circumstances. However, there are no guarantees to completely avoid the heap allocation. If you are in a situation where heap allocations are forbidden (for example, in a real-time context) the coroutine can be created and immediately suspended in a different thread, and then passed to the part of the program that needs to actually use the coroutine. Suspend and resume are guaranteed to not allocate any memory and have a cost comparable with an ordinary function call.

At the time of writing this book, compilers have experimental support for coroutines. Small experiments have shown promising results related to performance, showing that coroutines are friendly to the optimizer. However, I will not provide you with any benchmarks of coroutines in this book. Instead, I have shown you how stackless...