Fix some memory consumption issues

@@ -28,14 +28,18 @@ pub fn launch() -> Sender<(Arc<Pool>, Image)> {
         let mut workers = FuturesUnordered::new();
 
         loop {
-            select! {
-                image = rx_upload_worker.recv().fuse() => {
-                    match image {
-                        Err(_) => break,
-                        Ok((pool, image)) => workers.push(worker(pool, image)),
-                    }
-                },
-                _result = workers.next() => {},
+            if workers.len() <= 3 {
+                select! {
+                    image = rx_upload_worker.recv().fuse() => {
+                        match image {
+                            Err(_) => break,
+                            Ok((pool, image)) => workers.push(worker(pool, image)),
+                        }
+                    },
+                    _result = workers.next() => {},
+                }
+            } else {
+                workers.next().await;
             }
         }
 

@@ -21,8 +21,9 @@ pub(super) async fn upload_preview_logic( mut rx_canvas :broadcast::Receiver<Dom
             let context = canvas
                         . get_context("2d").unwrap().unwrap()
                         . dyn_into::<CanvasRenderingContext2d>().unwrap();
-            let image_width = upload.bitmap().width() as f64;
-            let image_height = upload.bitmap().height() as f64;
+            let bitmap = upload.bitmap();
+            let image_width = bitmap.width() as f64;
+            let image_height = bitmap.height() as f64;
             let canvas_width = canvas.width() as f64;
             let canvas_height = canvas.height() as f64;
 
@@ -41,9 +42,10 @@ pub(super) async fn upload_preview_logic( mut rx_canvas :broadcast::Receiver<Dom
 
             context
                 . draw_image_with_image_bitmap_and_dw_and_dh(
-                      &upload.bitmap()
+                      &bitmap
                     , ox, oy, width, height )
                 . unwrap();
+            bitmap.close();
         }
     }