async_nursery 0.5.0

//! Shows how you can save a nursery on a struct, so it's life and that of all spawned tasks is bound to it.
//! The example doesn't do anything when run.
//
#![ allow( unreachable_code, clippy::map_identity ) ]

use
{
	futures         :: { StreamExt                               } ,
	async_nursery   :: { Nursery, NurseryStream, Nurse, NurseExt } ,
	async_executors :: { SpawnHandle, SpawnHandleExt, JoinHandle } ,
};

type DynResult<T> = Result<T, Box< dyn std::error::Error + Send + Sync + 'static >>;


// This basically guarantees that when the connection dies, and this Connection
// object goes away. All the futures currently processing requests will be dropped.
// It doesn't make sense to do work to formulate a response for a connection that
// has died.
//
// Note that there is no integrated support for cooperative cancellation. If dropping
// the futures could leave the system in an inconsistent state, you'll have to implement
// cooperative cancelling in your tasks.
//
// Also you can't start inspecting the output of the tasks if you still want to spawn more.
//
// You can then implement Future or Stream for Connection, which will poll the nursery until all
// subtasks have finished their cleanup.
//
pub struct Connection
{
	nursery: Box< dyn Nurse< DynResult<()> > + Send > ,
	_handle: JoinHandle<DynResult<()>>                ,
}

impl Connection
{
	pub fn new( exec: impl SpawnHandle<DynResult<()>> + Clone + Send + 'static ) -> DynResult<Self>
	{
		let (nursery, nursery_stream) = Nursery::new( exec.clone() );

		let _handle = exec.spawn_handle( Self::listen_request_errors( nursery_stream ) )?;

		Ok( Self
		{
			nursery: Box::new( nursery ) ,
			_handle                      ,
		})
	}

	async fn listen_request_errors( mut nursery_stream: NurseryStream< DynResult<()> > ) -> DynResult<()>
	{
		while let Some(res) = nursery_stream.next().await
		{
			let _ = res.map_err( |e| /* handle error*/ e );
		}

		Ok(())
	}


	pub fn process( &self ) -> DynResult<()>
	{
		let _disconnect = false;

		while todo!() // let Some( request ) = incoming.next().await
		{
			self.nursery.nurse( async { /*process a request*/ Ok(()) } )?;

			// now if the connection goes away and the Connection object get's
			// dropped, the nursery will be dropped and any pending tasks spawned
			// on it will be dropped, so we don't leak ressources and don't
			// keep processing requests for connections that no longer exist.
			//
			if _disconnect { break }
		}

		Ok(())
	}
}



#[ async_std::main ]
//
async fn main() -> DynResult<()>
{
	Ok(())
}