fix(project-cache): Merge instead of replace project state channel in…

… upstream

relay-server/src/services/project_upstream.rs

@@ -79,7 +79,10 @@ impl UpstreamQuery for GetProjectStates {
 /// The wrapper struct for the incoming external requests which also keeps addition information.
 #[derive(Debug)]
 struct ProjectStateChannel {
+    // Main broadcast channel.
     channel: BroadcastChannel<ProjectFetchState>,
+    // Additional broadcast channels tracked from merge operations.
+    other: Vec<BroadcastChannel<ProjectFetchState>>,
     deadline: Instant,
     no_cache: bool,
     attempts: u64,
@@ -99,6 +102,7 @@ impl ProjectStateChannel {
         Self {
             no_cache,
             channel: sender.into_channel(),
+            other: Vec::new(),
             deadline: now + timeout,
             attempts: 0,
             errors: 0,
@@ -115,12 +119,35 @@ impl ProjectStateChannel {
     }
 
     pub fn send(self, state: ProjectFetchState) {
+        for channel in self.other {
+            channel.send(state.clone());
+        }
         self.channel.send(state)
     }
 
     pub fn expired(&self) -> bool {
         Instant::now() > self.deadline
     }
+
+    pub fn merge(&mut self, channel: ProjectStateChannel) {
+        let ProjectStateChannel {
+            channel,
+            other,
+            deadline,
+            no_cache,
+            attempts,
+            errors,
+            pending,
+        } = channel;
+
+        self.other.push(channel);
+        self.other.extend(other);
+        self.deadline = self.deadline.max(deadline);
+        self.no_cache |= no_cache;
+        self.attempts += attempts;
+        self.errors += errors;
+        self.pending += pending;
+    }
 }
 
 /// The map of project keys with their project state channels.
@@ -269,6 +296,23 @@ impl UpstreamProjectSourceService {
         }
     }
 
+    /// Merges a [`ProjectStateChannel`] into the existing list of tracked channels.
+    ///
+    /// A channel is removed when querying the upstream for the project,
+    /// when the upstream returns pending for this project it needs to be returned to
+    /// the list of channels. If there is already another request for the same project
+    /// outstanding those two requests must be merged.
+    fn merge_channel(&mut self, key: ProjectKey, channel: ProjectStateChannel) {
+        match self.state_channels.entry(key) {
+            Entry::Vacant(e) => {
+                e.insert(channel);
+            }
+            Entry::Occupied(mut e) => {
+                e.get_mut().merge(channel);
+            }
+        }
+    }
+
     /// Executes an upstream request to fetch project configs.
     ///
     /// This assumes that currently no request is running. If the upstream request fails or new
@@ -374,7 +418,7 @@ impl UpstreamProjectSourceService {
                         let mut result = "ok";
                         if response.pending.contains(&key) {
                             channel.pending += 1;
-                            self.state_channels.insert(key, channel);
+                            self.merge_channel(key, channel);
                             continue;
                         }
                         let state = response