Ability to choose b/w blocking and non-blocking client for reqwest

[thatdevsherry]

Problem

I had started working on the code I wrote involving prometheus sometime back. At that time the push function worked fine but now the code panics. The output of panic is:

thread 'main' panicked at 'Cannot drop a runtime in a context where blocking is not allowed. This happens when a runtime is dropped from within an asynchronous context.', /Users/phoenix/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.2.22/src/runtime/blocking/shutdown.rs:49:21
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
2020-11-14 08:42:05,631 TRACE [mio::sys::unix::kqueue] registering; token=Token(18446744073709551615); interests=Readable
2020-11-14 08:42:05,631 TRACE [mio::poll] registering with poller
2020-11-14 08:42:05,631 TRACE [reqwest::blocking::client] (ThreadId(12)) start runtime::block_on

Debugging

The last line made me figure out that rust-prometheus is using the blocking reqwest client. I was using the #[tokio::main] attribute to make the main() fn async. I believe using this and the blocking reqwest client causes this issue. Maybe the TRACE shows that is tries to use runtime::block_on which inside #[tokio::main] calls shutdown in tokio which has this panic line.

Would allowing the user to choose b/w blocking & non-blocking client solve this issue?

[breezewish]

Hi, there is an on-going PR that provides non-blocking clients. Would you like to try with it? #343

Also see #342

[thatdevsherry]

@breeswish oh my bad I should've searched the issues before, I'll keep an eye on issue #342 and PR #343