Stop holding lock during query execution (#1339)

Holding a lock during query execution can lead to a deadlock if
the transaction holding it is blocked by another transaction and
that other transaction can't proceed because it can't get the lock
that is held by the first transaction.

Fixes #1290

Signed-off-by: Piotr Jastrzebski <piotr@chiselstrike.com>

libsql-server/src/rpc/proxy.rs

@@ -637,20 +637,24 @@ impl Proxy for ProxyService {
                 }
             })?;
 
-        let lock = self.clients.upgradable_read().await;
-        let conn = match lock.get(&client_id) {
-            Some(conn) => conn.clone(),
-            None => {
-                tracing::debug!("connected: {client_id}");
-                match connection_maker.create().await {
-                    Ok(conn) => {
-                        assert!(conn.is_primary());
-                        let conn = Arc::new(TimeoutConnection::new(conn));
-                        let mut lock = RwLockUpgradableReadGuard::upgrade(lock).await;
-                        lock.insert(client_id, conn.clone());
-                        conn
+        let conn = {
+            let lock = self.clients.upgradable_read().await;
+            match lock.get(&client_id) {
+                Some(conn) => conn.clone(),
+                None => {
+                    tracing::debug!("connected: {client_id}");
+                    match connection_maker.create().await {
+                        Ok(conn) => {
+                            assert!(conn.is_primary());
+                            let conn = Arc::new(TimeoutConnection::new(conn));
+                            let mut lock = RwLockUpgradableReadGuard::upgrade(lock).await;
+                            lock.insert(client_id, conn.clone());
+                            conn
+                        }
+                        Err(e) => {
+                            return Err(tonic::Status::new(tonic::Code::Internal, e.to_string()))
+                        }
                     }
-                    Err(e) => return Err(tonic::Status::new(tonic::Code::Internal, e.to_string())),
                 }
             }
         };