Are file I/O asynchronous in Warp ? On a related topic could you tell us about coroutines/fibres in D ... How are they implemented ? Can they be called from C

Are file I/O asynchronous in Warp ? On a related topic could you tell us about coroutines/fibres in D ... How are they implemented ? Can they be called from C ? are they are used in D's standard library, examples of a few notable use cases (I guess one would be Vibe.d), examples of asynchronous idioms in D. Since that's a lot of questions, pointing to documents would be fine too. ..and thanks for answering questions here.