Close gRPC getpage streams on shutdown

Some tests were failing, because pageserver didn't shut down promptly.
Tonic server graceful shutdown was a little too graceful; any open
streams linger until they're closed. Check the cancellation token
while waiting for next request, and close the stream if
shutdown/cancellation was requested.

pageserver/src/page_service.rs

@@ -3170,6 +3170,7 @@ where
 pub struct GrpcPageServiceHandler {
     tenant_manager: Arc<TenantManager>,
     ctx: RequestContext,
+    cancel: CancellationToken,
     gate_guard: GateGuard,
     get_vectored_concurrent_io: GetVectoredConcurrentIo,
 }
@@ -3222,6 +3223,7 @@ impl GrpcPageServiceHandler {
         let page_service_handler = GrpcPageServiceHandler {
             tenant_manager,
             ctx,
+            cancel: cancel.clone(),
             gate_guard: gate.enter().expect("gate was just created"),
             get_vectored_concurrent_io,
         };
@@ -3672,6 +3674,7 @@ impl proto::PageService for GrpcPageServiceHandler {
         // Spawn a task to handle the GetPageRequest stream.
         let span = Span::current();
         let ctx = self.ctx.attached_child();
+        let cancel = self.cancel.clone();
         let mut reqs = req.into_inner();
 
         let resps = async_stream::try_stream! {
@@ -3679,7 +3682,20 @@ impl proto::PageService for GrpcPageServiceHandler {
                 .get(ttid.tenant_id, ttid.timeline_id, shard_selector)
                 .await?
                 .downgrade();
-            while let Some(req) = reqs.message().await? {
+
+            loop {
+                let req = tokio::select! {
+                    req = reqs.message() => req,
+                    _ = cancel.cancelled() => {
+                        tracing::info!("closing getpages stream due to shutdown");
+                        break;
+                    },
+                };
+                let req = if let Some(req) = req? {
+                    req
+                } else {
+                    break;
+                };
                 let req_id = req.request_id;
                 let result = Self::get_page(&ctx, &timeline, req, io_concurrency.clone())
                     .instrument(span.clone()) // propagate request span