fix(subscriber): Don't save poll_ops if no-one is receiving them

Do not record poll_ops if there are no current connected clients
(watchers). Without this `Aggregator::poll_ops` would grow forever.

Follow up to tokio-rs#311 and
fix for these two:
- tokio-rs#184
- tokio-rs#500

console-subscriber/src/aggregator/mod.rs

@@ -1,21 +1,22 @@
-use super::{Command, Event, Shared, Watch};
-use crate::{
-    stats::{self, Unsent},
-    ToProto, WatchRequest,
-};
-use console_api as proto;
-use proto::resources::resource;
-use tokio::sync::{mpsc, Notify};
-
 use std::{
     sync::{
         atomic::{AtomicBool, Ordering::*},
         Arc,
     },
     time::{Duration, Instant},
 };
+
+use console_api as proto;
+use proto::resources::resource;
+use tokio::sync::{mpsc, Notify};
 use tracing_core::{span::Id, Metadata};
 
+use super::{Command, Event, Shared, Watch};
+use crate::{
+    stats::{self, Unsent},
+    ToProto, WatchRequest,
+};
+
 mod id_data;
 mod shrink;
 use self::id_data::{IdData, Include};
@@ -269,6 +270,9 @@ impl Aggregator {
             .drop_closed(&mut self.resource_stats, now, self.retention, has_watchers);
         self.async_ops
             .drop_closed(&mut self.async_op_stats, now, self.retention, has_watchers);
+        if !has_watchers && !self.poll_ops.is_empty() {
+            self.poll_ops.clear();
+        }
     }
 
     /// Add the task subscription to the watchers after sending the first update
@@ -305,14 +309,10 @@ impl Aggregator {
     }
 
     fn resource_update(&mut self, include: Include) -> proto::resources::ResourceUpdate {
-        let new_poll_ops = match include {
-            Include::All => self.poll_ops.clone(),
-            Include::UpdatedOnly => std::mem::take(&mut self.poll_ops),
-        };
         proto::resources::ResourceUpdate {
             new_resources: self.resources.as_proto_list(include, &self.base_time),
             stats_update: self.resource_stats.as_proto(include, &self.base_time),
-            new_poll_ops,
+            new_poll_ops: std::mem::take(&mut self.poll_ops),
             dropped_events: self.shared.dropped_resources.swap(0, AcqRel) as u64,
         }
     }
@@ -472,6 +472,9 @@ impl Aggregator {
                 task_id,
                 is_ready,
             } => {
+                if self.watchers.is_empty() {
+                    return;
+                }
                 let poll_op = proto::resources::PollOp {
                     metadata: Some(metadata.into()),
                     resource_id: Some(resource_id.into()),