[Nearby Connections] Add methods to shutdown executors in bwu_manager

Adding methods that allow us to shutdown executors in bwu_manager
during Nearby Connections shutdown process to prevent potential crashes.

PiperOrigin-RevId: 466425604

connections/implementation/bwu_manager.cc

@@ -129,8 +129,7 @@ void BwuManager::Shutdown() {
       V1Frame::BANDWIDTH_UPGRADE_NEGOTIATION, this);
 
   // Stop all the ongoing Runnables (as gracefully as possible).
-  alarm_executor_.Shutdown();
-  serial_executor_.Shutdown();
+  ShutdownExecutors();
 
   // After worker threads are down we became exclusive owners of data and
   // may access it from current thread.
@@ -162,6 +161,11 @@ void BwuManager::InvokeOnIncomingConnectionForTesting(
   OnIncomingConnection(client, std::move(mutable_connection));
 }
 
+void BwuManager::ShutdownExecutors() {
+  alarm_executor_.Shutdown();
+  serial_executor_.Shutdown();
+}
+
 void BwuManager::InitiateBwuForEndpoint(ClientProxy* client,
                                         const std::string& endpoint_id,
                                         Medium new_medium) {

connections/implementation/bwu_manager.h

@@ -108,6 +108,11 @@ class BwuManager : public EndpointManager::FrameProcessor {
       ClientProxy* client,
       std::unique_ptr<BwuHandler::IncomingSocketConnection> mutable_connection);
 
+  // Shutdown the executors during Nearby Connections shutdown process before
+  // Core objects destruction so that no task will be run/posted after
+  // ClientProxy objects are deleted.
+  void ShutdownExecutors();
+
  private:
   static constexpr absl::Duration kReadClientIntroductionFrameTimeout =
       absl::Seconds(5);

connections/implementation/mock_service_controller.h

@@ -83,6 +83,8 @@ class MockServiceController : public ServiceController {
   MOCK_METHOD(void, DisconnectFromEndpoint,
               (ClientProxy * client, const std::string& endpoint_id),
               (override));
+
+  MOCK_METHOD(void, ShutdownBwuManagerExecutors, (), (override));
 };
 
 }  // namespace connections

connections/implementation/offline_service_controller.cc

@@ -142,6 +142,10 @@ void OfflineServiceController::DisconnectFromEndpoint(
   endpoint_manager_.UnregisterEndpoint(client, endpoint_id);
 }
 
+void OfflineServiceController::ShutdownBwuManagerExecutors() {
+  bwu_manager_.ShutdownExecutors();
+}
+
 }  // namespace connections
 }  // namespace nearby
 }  // namespace location

connections/implementation/offline_service_controller.h

@@ -77,6 +77,8 @@ class OfflineServiceController : public ServiceController {
 
   void Stop() override;
 
+  void ShutdownBwuManagerExecutors() override;
+
  private:
   // Note that the order of declaration of these is crucial, because we depend
   // on the destructors running (strictly) in the reverse order; a deviation

connections/implementation/service_controller.h

@@ -56,6 +56,10 @@ class ServiceController {
   // controller are affected.
   virtual void Stop() = 0;
 
+  // Shuts down executors in the BwuManager. After that no tasks should be
+  // running on or posted to BwuManager.
+  virtual void ShutdownBwuManagerExecutors() = 0;
+
   // Starts advertising an endpoint for a local app.
   virtual Status StartAdvertising(ClientProxy* client,
                                   const std::string& service_id,

connections/implementation/service_controller_router.cc

@@ -368,6 +368,7 @@ void ServiceControllerRouter::FinishClientSession(ClientProxy* client) {
   // Stop any advertising and discovery that may be underway due to this client.
   GetServiceController()->StopAdvertising(client);
   GetServiceController()->StopDiscovery(client);
+  GetServiceController()->ShutdownBwuManagerExecutors();
 
   // Finally, clear all state maintained by this client.
   client->Reset();