Reviewer comments

src/core/ext/filters/client_channel/client_channel.cc

@@ -171,34 +171,22 @@ class ChannelData {
                                       grpc_connectivity_state* state,
                                       grpc_closure* on_complete,
                                       grpc_closure* watcher_timer_init) {
-    auto watcher = MakeRefCounted<ExternalConnectivityWatcher>(
+    auto watcher = new ExternalConnectivityWatcher(
         this, pollent, state, on_complete, watcher_timer_init);
     {
       MutexLock lock(&external_watchers_mu_);
-      // Will be deleted when the watch is complete.
-      GPR_ASSERT(external_watchers_[on_complete] == nullptr);
-      // Pass a ref to the external_watchers_ map. We are taking an additional
-      // ref on the watcher so that we can maintain lifetime guarantees when
-      // watcher->Start() is called after the critical section.
-      external_watchers_[on_complete] = watcher;
+      // Store a ref to the watcher in the external_watchers_ map.
+      watcher->AddWatcherToExternalWatchersMapLocked(&external_watchers_,
+                                                     on_complete);
     }
+    // Pass the ref from creating the object to Start().
     watcher->Start();
   }
 
   void RemoveExternalConnectivityWatcher(grpc_closure* on_complete,
                                          bool cancel) {
-    RefCountedPtr<ExternalConnectivityWatcher> watcher;
-    {
-      MutexLock lock(&external_watchers_mu_);
-      auto it = external_watchers_.find(on_complete);
-      if (it != external_watchers_.end()) {
-        watcher = std::move(it->second);
-        external_watchers_.erase(it);
-      }
-    }
-    // watcher->Cancel() will hop into the WorkSerializer, so we have to unlock
-    // the mutex before calling it.
-    if (watcher != nullptr && cancel) watcher->Cancel();
+    ExternalConnectivityWatcher::RemoveWatcherFromExternalWatchersMap(
+        &external_watchers_mu_, &external_watchers_, on_complete, cancel);
   }
 
   int NumExternalConnectivityWatchers() const {
@@ -229,6 +217,22 @@ class ChannelData {
 
     ~ExternalConnectivityWatcher();
 
+    // Adds the watcher to the external_watchers_ map. Synchronized by
+    // external_watchers_mu_
+    void AddWatcherToExternalWatchersMapLocked(
+        std::map<grpc_closure*, RefCountedPtr<ExternalConnectivityWatcher>>*
+            external_watchers,
+        grpc_closure* on_complete);
+
+    // Removes the watcher from the external_watchers_ map.
+    static void RemoveWatcherFromExternalWatchersMap(
+        Mutex* external_watchers_mu,
+        std::map<grpc_closure*, RefCountedPtr<ExternalConnectivityWatcher>>*
+            external_watchers,
+        grpc_closure* on_complete, bool cancel);
+
+    // Starts the watch. Consumes the ref from the creation of the
+    // ExternalConnectivityWatcher object.
     void Start();
 
     void Notify(grpc_connectivity_state state) override;
@@ -236,6 +240,8 @@ class ChannelData {
     void Cancel();
 
    private:
+    // Adds the watcher to state_tracker_. Consumes the ref that is passed to it
+    // from Start().
     void AddWatcherLocked();
     void RemoveWatcherLocked();
 
@@ -1184,13 +1190,44 @@ ChannelData::ExternalConnectivityWatcher::~ExternalConnectivityWatcher() {
                            "ExternalConnectivityWatcher");
 }
 
+void ChannelData::ExternalConnectivityWatcher::
+    AddWatcherToExternalWatchersMapLocked(
+        std::map<grpc_closure*, RefCountedPtr<ExternalConnectivityWatcher>>*
+            external_watchers,
+        grpc_closure* on_complete) {
+  // Will be deleted when the watch is complete.
+  GPR_ASSERT((*external_watchers)[on_complete] == nullptr);
+  (*external_watchers)[on_complete] =
+      Ref(DEBUG_LOCATION, "AddWatcherToExternalWatchersMapLocked");
+}
+
+void ChannelData::ExternalConnectivityWatcher::
+    RemoveWatcherFromExternalWatchersMap(
+        Mutex* external_watchers_mu,
+        std::map<grpc_closure*, RefCountedPtr<ExternalConnectivityWatcher>>*
+            external_watchers,
+        grpc_closure* on_complete, bool cancel) {
+  RefCountedPtr<ExternalConnectivityWatcher> watcher;
+  {
+    MutexLock lock(external_watchers_mu);
+    auto it = (*external_watchers).find(on_complete);
+    if (it != (*external_watchers).end()) {
+      watcher = std::move(it->second);
+      (*external_watchers).erase(it);
+    }
+  }
+  if (watcher != nullptr && cancel) {
+    watcher->Cancel();
+  }
+}
+
 void ChannelData::ExternalConnectivityWatcher::Start() {
-  // Ref owned by the lambda
-  Ref(DEBUG_LOCATION, "Start").release();
+  // No need to take a ref since Start() consumes the ref from the
+  // creation of the object.
   chand_->work_serializer_->Run(
       [this]() {
+        // The ref is passed to AddWatcherLocked().
         AddWatcherLocked();
-        Unref(DEBUG_LOCATION, "Start");
       },
       DEBUG_LOCATION);
 }
@@ -1230,10 +1267,9 @@ void ChannelData::ExternalConnectivityWatcher::Cancel() {
 
 void ChannelData::ExternalConnectivityWatcher::AddWatcherLocked() {
   Closure::Run(DEBUG_LOCATION, watcher_timer_init_, GRPC_ERROR_NONE);
-  // Add new watcher.
+  // Add new watcher. Pass the ref of the object from creation to OrphanablePtr.
   chand_->state_tracker_.AddWatcher(
-      initial_state_,
-      OrphanablePtr<ConnectivityStateWatcherInterface>(Ref().release()));
+      initial_state_, OrphanablePtr<ConnectivityStateWatcherInterface>(this));
 }
 
 void ChannelData::ExternalConnectivityWatcher::RemoveWatcherLocked() {