timeline: add await_initial_logical_size

pageserver/src/tenant/timeline.rs

@@ -1903,6 +1903,7 @@ impl Timeline {
             .set((calculated_size, metrics_guard.calculation_result_saved()))
             .ok()
             .expect("only this task sets it");
+        self.current_logical_size.initialized.notify_one();
     }
 
     pub fn spawn_ondemand_logical_size_calculation(
@@ -3104,6 +3105,24 @@ impl Timeline {
 
         Ok(image_layers)
     }
+
+    /// Wait until the background initial logical size calculation is complete, or
+    /// this Timeline is shut down.  Calling this function will cause the initial
+    /// logical size calculation to skip waiting for the background jobs barrier.
+    pub(crate) async fn await_initial_logical_size(self: Arc<Self>) {
+        if let Some(await_bg_cancel) = self
+            .current_logical_size
+            .cancel_wait_for_background_loop_concurrency_limit_semaphore
+            .get()
+        {
+            await_bg_cancel.cancel();
+        }
+
+        tokio::select!(
+            _ = self.current_logical_size.initialized.notified() => {},
+            _ = self.cancel.cancelled() => {}
+        )
+    }
 }
 
 #[derive(Default)]

pageserver/src/tenant/timeline/logical_size.rs

@@ -34,6 +34,9 @@ pub(super) struct LogicalSize {
     pub(crate) cancel_wait_for_background_loop_concurrency_limit_semaphore:
         OnceCell<CancellationToken>,
 
+    /// Once the initial logical size is initialized, this is notified.
+    pub(crate) initialized: tokio::sync::Notify,
+
     /// Latest Lsn that has its size uncalculated, could be absent for freshly created timelines.
     pub initial_part_end: Option<Lsn>,
 
@@ -125,6 +128,7 @@ impl LogicalSize {
             initial_part_end: None,
             size_added_after_initial: AtomicI64::new(0),
             did_return_approximate_to_walreceiver: AtomicBool::new(false),
+            initialized: tokio::sync::Notify::new(),
         }
     }
 
@@ -135,6 +139,7 @@ impl LogicalSize {
             initial_part_end: Some(compute_to),
             size_added_after_initial: AtomicI64::new(0),
             did_return_approximate_to_walreceiver: AtomicBool::new(false),
+            initialized: tokio::sync::Notify::new(),
         }
     }