tokio compatibility

[bernardoaraujor]

I working on this PR to braidpool.

Since braidpool project is using tokio, I forked rust-bitcoincore-zmq into tokio-bitcoincore-zmq.

I was wondering if this is a desirable feature for the upstream crate?

[antonilol]

great idea! i have tried in the past to make this library work with async because zmq is mostly I/O and technically does not need one thread per subscriber, but just smashing an async runtime (i tried tokio) on it did not work (obviously, but i was exploring async Rust for the first time then) as it blocked the executor. i just looked around again and found https://github.com/rdelfin/async-zmq, this also does not force a specific async runtime upon users.
i will try around with this a bit and look how it fits in with the synchronous code, because i dont want to remove that, thinking about an 'async' feature flag, as it comes with extra dependencies not needed otherwise

[antonilol]

did you test it with less executor threads than endpoints? i believe it will lock up because subscribe_internal is blocking (it uses a loop).
if you for example want to open a tcp socket in async rust you have to use an async tcp library (tokio has them), not a sync one line std::net::TcpStream as it will block a thread of the executor.

(async_zmq fits really well in my existing code, maybe i can push some testing code already today or tomorrow, will push this to a new branch called 'async')

[antonilol]

just implemented it, feel free to review for anything like questions, feature requests or maybe i missed something
#4

[bernardoaraujor]

didn't review everything, but seems to be on the right direction

I'm already able to use subscribe_async and it's working as expected, so that fulfills the needs for braidpool.

therefore I'm archiving my tokio-compatible fork in favor of this upstream project.

[antonilol]

I'm already able to use subscribe_async and it's working as expected, so that fulfills the needs for braidpool.

good to hear, just a heads up, subscribe_async has been renamed to subscribe_single_async for consistency with the existing subscribe functions

[antonilol]

published version 1.3.0 to crates.io, the feature gates functions and structs are not showing on docs.rs, will fix this soon