suggestion from omar - 2 - (un)maintain methods

removed write_maintained_connections and added maintain & unmaintain methods.

mm2src/coins/utxo/rpc_clients/electrum_rpc/connection_manager/manager.rs

@@ -280,15 +280,7 @@ impl ConnectionManager {
         let all_connections = self.read_connections();
         let connection_ctx = unwrap_or_return!(all_connections.get(server_address));
 
-        if self.read_maintained_connections().contains_key(&connection_ctx.id) {
-            // If the connection was maintained, remove it from the maintained connections.
-            let mut maintained_connections = self.write_maintained_connections();
-            maintained_connections.remove(&connection_ctx.id);
-            // And notify the background task if we fell below the `min_connected` threshold.
-            if (maintained_connections.len() as u32) < self.config().min_connected {
-                self.notify_below_min_connected()
-            }
-        }
+        self.unmaintain(connection_ctx.id);
 
         let abandoned_subs = connection_ctx.disconnected();
         // Re-subscribe the abandoned addresses using the client.
@@ -407,8 +399,6 @@ impl ConnectionManager {
                 let client = unwrap_or_return!(self.get_client());
                 // Sort the candidate connections by their priority/ID.
                 candidate_connections.sort_by_key(|(_, priority)| *priority);
-
-                // Pick each chunk of connections and establish them concurrently.
                 for (connection, _) in candidate_connections {
                     let address = connection.address().to_string();
                     let connection_id = unwrap_or_continue!(self.read_connections().get(&address)).id;
@@ -434,12 +424,7 @@ impl ConnectionManager {
                             }
                             continue;
                         }
-                        let mut maintained_connections = self.write_maintained_connections();
-                        maintained_connections.insert(connection_id, address);
-                        // If we have reached the `max_connected` threshold then remove the lowest priority connection.
-                        if !maintained_connections_size < self.config().max_connected {
-                            maintained_connections.remove(&lowest_priority_connection_id);
-                        }
+                        self.maintain(connection_id, address);
                     } else {
                         // If any of the two conditions on the `if` statement above are not met, there is nothing to do.
                         // At this point we have already collected `max_connected` connections and also the current connection
@@ -493,8 +478,29 @@ impl ConnectionManager {
     }
 
     #[inline]
-    fn write_maintained_connections(&self) -> RwLockWriteGuard<BTreeMap<ID, String>> {
-        self.0.maintained_connections.write().unwrap()
+    fn maintain(&self, id: ID, server_address: String) {
+        let mut maintained_connections = self.0.maintained_connections.write().unwrap();
+        maintained_connections.insert(id, server_address);
+        // If we have reached the `max_connected` threshold then remove the lowest priority connection.
+        if (maintained_connections.len() as u32) > self.config().max_connected {
+            let lowest_priority_connection_id = *maintained_connections.keys().next_back().unwrap_or(&u32::MAX);
+            maintained_connections.remove(&lowest_priority_connection_id);
+        }
+    }
+
+    #[inline]
+    fn unmaintain(&self, id: ID) {
+        // To avoid write locking the maintained connections, just make sure the connection is actually maintained first.
+        let is_maintained = self.read_maintained_connections().contains_key(&id);
+        if is_maintained {
+            // If the connection was maintained, remove it from the maintained connections.
+            let mut maintained_connections = self.0.maintained_connections.write().unwrap();
+            maintained_connections.remove(&id);
+            // And notify the background task if we fell below the `min_connected` threshold.
+            if (maintained_connections.len() as u32) < self.config().min_connected {
+                self.notify_below_min_connected()
+            }
+        }
     }
 
     #[inline]