Comment by mplanchard

You don’t have to make everything Send/Sync if you don’t need to. Use tokio’s local runtime and spawn_local(), or use one of the other async runtimes.

You also don’t need to spawn() futures to await them. Spawn enables parallelism on the multithreaded runtime, holding join handles, etc. If all you need is to execute concurrent code, though, the various combinators and functions in the futures crate lets you do so without having hard requirements on Send/Sync. The large majority of the concurrent code I write uses nothing specific from the tokio crate, including spawn.

As is often the case in rust, the compiler is also telling you the correct thing. If you’re using the multithreaded runtime and spawning, your code may execute in another thread, so it has to be Send/Sync, and since the ownership of the future is transferred to the executor, it must also be ‘static.