track uncounted downloads

Author: pietroalbini

src/downloads_counter.rs

@@ -199,6 +199,10 @@ impl DownloadsCounter {
     pub fn shards_count(&self) -> usize {
         self.inner.shards().len()
     }
+
+    pub(crate) fn pending_count(&self) -> i64 {
+        self.pending_count.load(Ordering::SeqCst)
+    }
 }
 
 #[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]

src/metrics/instance.rs

@@ -44,6 +44,8 @@ metrics! {
         pub downloads_unconditional_redirects_total: IntCounter,
         /// Number of download requests with a non-canonical crate name.
         pub downloads_non_canonical_crate_name_total: IntCounter,
+        /// Number of download requests that are not counted yet.
+        downloads_not_counted_total: IntGauge,
     }
 
     // All instance metrics will be prefixed with this namespace.
@@ -58,6 +60,9 @@ impl InstanceMetrics {
             self.refresh_pool_stats("follower", follower)?;
         }
 
+        self.downloads_not_counted_total
+            .set(app.downloads_counter.pending_count());
+
         Ok(self.registry.gather())
     }