Add a generic public FutureSpawner in LDK directly

In the next commit we'll use this to spawn async persistence
operations in the background, but for now we just move the
`lightning-block-sync` `FutureSpawner` into `lightning`.

Author: TheBlueMatt

lightning-block-sync/src/gossip.rs

@@ -10,11 +10,10 @@ use bitcoin::hash_types::BlockHash;
 use bitcoin::transaction::{OutPoint, TxOut};
 
 use lightning::ln::peer_handler::APeerManager;
-
 use lightning::routing::gossip::{NetworkGraph, P2PGossipSync};
 use lightning::routing::utxo::{UtxoFuture, UtxoLookup, UtxoLookupError, UtxoResult};
-
 use lightning::util::logger::Logger;
+use lightning::util::native_async::FutureSpawner;
 
 use std::collections::VecDeque;
 use std::future::Future;
@@ -43,17 +42,6 @@ pub trait UtxoSource: BlockSource + 'static {
 	fn is_output_unspent<'a>(&'a self, outpoint: OutPoint) -> AsyncBlockSourceResult<'a, bool>;
 }
 
-/// A generic trait which is able to spawn futures in the background.
-///
-/// If the `tokio` feature is enabled, this is implemented on `TokioSpawner` struct which
-/// delegates to `tokio::spawn()`.
-pub trait FutureSpawner: Send + Sync + 'static {
-	/// Spawns the given future as a background task.
-	///
-	/// This method MUST NOT block on the given future immediately.
-	fn spawn<T: Future<Output = ()> + Send + 'static>(&self, future: T);
-}
-
 #[cfg(feature = "tokio")]
 /// A trivial [`FutureSpawner`] which delegates to `tokio::spawn`.
 pub struct TokioSpawner;

lightning/src/util/mod.rs

@@ -26,6 +26,7 @@ pub mod base32;
 pub(crate) mod base32;
 pub mod errors;
 pub mod message_signing;
+pub mod native_async;
 pub mod persist;
 pub mod scid_utils;
 pub mod ser;

lightning/src/util/native_async.rs

@@ -0,0 +1,19 @@
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! This module contains a few public utility which are used to run LDK in a native Rust async
+//! environment.
+
+use crate::util::async_poll::MaybeSend;
+use core::future::Future;
+
+/// A generic trait which is able to spawn futures in the background.
+pub trait FutureSpawner: Send + Sync + 'static {
+	/// Spawns the given future as a background task.
+	///
+	/// This method MUST NOT block on the given future immediately.
+	fn spawn<T: Future<Output = ()> + MaybeSend + 'static>(&self, future: T);
+}