Improve sync_wallet docs and use current thread runtime for LDK

We improve the docs, in particular mentioning now that users should
always prefer background syncing over blocking sync if possible.

Moreover, as we already have a current thread runtime setup for the BDK
wallet, we now also use it to sync the LDK wallet. This is a good idea
as we want to avoid calling `block_on` on our main runtime where
possible, which is always in danger of (temporarily or permanently)
blocking the world if something goes wrong.

Author: tnull

src/lib.rs

@@ -1342,15 +1342,17 @@ impl<K: KVStore + Sync + Send + 'static> Node<K> {
 		}
 	}
 
-	/// Sync the LDK and BDK wallets with the current chain state.
+	/// Manually sync the LDK and BDK wallets with the current chain state.
 	///
-	/// Note that the wallets will be also synced regularly in the background.
+	/// **Note:** The wallets are regularly synced in the background, which is configurable via
+	/// [`Config::onchain_wallet_sync_interval_secs`] and [`Config::wallet_sync_interval_secs`].
+	/// Therefore, using this blocking sync method is almost always redudant and should be avoided
+	/// where possible.
 	pub fn sync_wallets(&self) -> Result<(), Error> {
 		let rt_lock = self.runtime.read().unwrap();
 		if rt_lock.is_none() {
 			return Err(Error::NotRunning);
 		}
-		let runtime = rt_lock.as_ref().unwrap();
 
 		let wallet = Arc::clone(&self.wallet);
 		let tx_sync = Arc::clone(&self.tx_sync);
@@ -1373,39 +1375,31 @@ impl<K: KVStore + Sync + Send + 'static> Node<K> {
 								"Sync of on-chain wallet finished in {}ms.",
 								now.elapsed().as_millis()
 							);
-							Ok(())
 						}
 						Err(e) => {
 							log_error!(sync_logger, "Sync of on-chain wallet failed: {}", e);
-							Err(e)
+							return Err(e);
+						}
+					};
+
+					let now = Instant::now();
+					match tx_sync.sync(confirmables).await {
+						Ok(()) => {
+							log_info!(
+								sync_logger,
+								"Sync of Lightning wallet finished in {}ms.",
+								now.elapsed().as_millis()
+							);
+							Ok(())
+						}
+						Err(e) => {
+							log_error!(sync_logger, "Sync of Lightning wallet failed: {}", e);
+							Err(e.into())
 						}
 					}
 				},
 			)
-		})?;
-
-		let sync_logger = Arc::clone(&self.logger);
-		tokio::task::block_in_place(move || {
-			runtime.block_on(async move {
-				let now = Instant::now();
-				match tx_sync.sync(confirmables).await {
-					Ok(()) => {
-						log_info!(
-							sync_logger,
-							"Sync of Lightning wallet finished in {}ms.",
-							now.elapsed().as_millis()
-						);
-						Ok(())
-					}
-					Err(e) => {
-						log_error!(sync_logger, "Sync of Lightning wallet failed: {}", e);
-						Err(e)
-					}
-				}
-			})
-		})?;
-
-		Ok(())
+		})
 	}
 
 	/// Close a previously opened channel.