Execution of async code in a new thread

[dzharkov]

In current implementation execution of coroutine code starts in the same thread and continues until first execution point.
Probably it's worth to run it on a thread-pool (it could be another parameter with some sensible default value, e.g. ForkJoinPool.commonPool())

[ilya-g]

It should be noted that in .NET async has similar behavior — it runs synchronously until the first await is encountered. It even can continue to execute synchronously in case if the awaitable being awaited is already completed. It all helps to minimize unnecessary thread switches.

In case if one needs to postpone the execution, it can be done with Task.Yield awaitable:

await Task.Yield()

[elizarov]

The decision was to always require an explicit specification of execution policy for most coroutine builder. So launch(Here) { ... } would execute like in .NET (until first suspend), while launch (CommonPool) { ... } would immediate schedule into a background thread. Other execution policies can be defined by user. The only exception is a future { } which goes to CommonPool by default.