Can runtime arguments be made optional?

[dfoxfranke]

Having to pass a tokio::runtime::Handle in order to construct an AsyncResolver (or a TokioConnectionProvider) is slightly awkward because it means that programs which use AsyncResolver can't be written with a main function declared using #[tokio::main]. Programs which use #[tokio::main] never explicitly construct a tokio runtime and have no means of obtaining a handle to the one that tokio implicitly constructs. Could the runtime argument be made Optional, such that if None is passed then the resolver will just spawn tasks on the default executor using tokio::spawn()?

[bluejekyll]

I'd consider it. I hate relying on thread local storage for this stuff, it makes testing really difficult. Let me review our options in this area.

It might be that we could pass in a TokioTlsHandle that carries no data, and just calls tokio::spawn. I think that would be fine. And that could be the default you're looking for.

[bluejekyll]

Ok, I think we're going to handle this in the tokio library itself: tokio-rs/tokio#2040

Once that or something like it lands, we can then have a default method on trust-dns-resolver then takes the thread-local instantiated Handle, which will work in this case.

[bluejekyll]

FYI, with https://docs.rs/tokio/0.2.8/tokio/runtime/struct.Handle.html#method.current now in Tokio, users should be able to get a handle to the current runtime in a #[tokio::main]. I'll add a function for initializing trust-dns-resolver so that the extra code isn't necessary.

[gzbakku]

has this problem been resolved
how to do this??

[djc]

I think this has been solved? At least you can in 0.19 instantiate a TokioAsyncResolver that doesn't require you to pass in a Handle.

[dfoxfranke]

Yes, this should be closed with the addition of the tokio_from_system_conf() constructor.