only apply new semaphore to thumbnails

otherwise it blocks every other api query, including the large cover
art, since the tokio semaphore is fair

src/model/song.rs

@@ -64,8 +64,12 @@ use crate::subsonic;
 use adw::{prelude::*, subclass::prelude::*};
 use glib::Object;
 use gtk::{gdk, glib};
+use tokio::sync::Semaphore;
 use tracing::{event, Level};
 
+// only fetch 20 thumbnails at a time
+static SEM: Semaphore = Semaphore::const_new(20);
+
 glib::wrapper! {
     pub struct Song(ObjectSubclass<imp::Song>);
 }
@@ -95,6 +99,8 @@ impl Song {
             song.imp()
                 .thumbnail_loading
                 .replace(Some(glib::spawn_future_local(async move {
+                    let _permit = SEM.acquire().await.unwrap();
+
                     let bytes = match api
                         .cover_art(&id, Some(50 * scale_factor)) // see pixel-size in
                         // play_queue_song.blp

src/subsonic.rs

@@ -6,8 +6,6 @@ pub use album_list::AlbumListType;
 use adw::glib;
 use bytes::Bytes;
 use rand::Rng;
-use std::sync::Arc;
-use tokio::sync::Semaphore;
 use tracing::{event, Level};
 
 fn runtime() -> &'static tokio::runtime::Runtime {
@@ -58,7 +56,6 @@ impl From<reqwest::Error> for Error {
 pub struct Client {
     client: reqwest::Client,
     base_url: reqwest::Url,
-    sem: Arc<Semaphore>,
 }
 
 fn random_salt(length: usize) -> String {
@@ -109,7 +106,6 @@ impl Client {
                 .user_agent(crate::USER_AGENT)
                 .build()?,
             base_url,
-            sem: Arc::new(Semaphore::new(20)), // 20 requests at one time
         })
     }
 
@@ -125,10 +121,7 @@ impl Client {
         // note that this is why those silly bounds on T are needed, because we're
         // sending back the result of the query from another thread
         let future = request.send();
-        let sem = Arc::clone(&self.sem);
         runtime().spawn(async move {
-            let _permit = sem.acquire().await.unwrap();
-
             // wrap this logic in a fn so we can use ?
             async fn perform<T: serde::de::DeserializeOwned + Send + 'static>(
                 response: Result<reqwest::Response, reqwest::Error>,
@@ -202,10 +195,7 @@ impl Client {
         let (sender, receiver) = async_channel::bounded(1);
 
         let future = self.client.get(self.cover_art_url(id, size)).send();
-        let sem = Arc::clone(&self.sem);
         runtime().spawn(async move {
-            let _permit = sem.acquire().await.unwrap();
-
             async fn perform(
                 response: Result<reqwest::Response, reqwest::Error>,
             ) -> Result<Bytes, Error> {