server: wait workers to start before draining parent.

include/envoy/server/listener_manager.h

@@ -202,8 +202,9 @@ class ListenerManager {
   /**
    * Start all workers accepting new connections on all added listeners.
    * @param guard_dog supplies the guard dog to use for thread watching.
+   * @param callback supplies the callback to complete server initialization.
    */
-  virtual void startWorkers(GuardDog& guard_dog) PURE;
+  virtual void startWorkers(GuardDog& guard_dog, std::function<void()> callback) PURE;
 
   /**
    * Stop all listeners from accepting new connections without actually removing any of them. This

source/server/listener_hooks.h

@@ -22,6 +22,11 @@ class ListenerHooks {
    */
   virtual void onWorkerListenerRemoved() PURE;
 
+  /**
+   * Called when all workers have started.
+   */
+  virtual void onWorkersStarted() PURE;
+
   /**
    * Called when the Runtime::ScopedLoaderSingleton is created by the server.
    */
@@ -36,6 +41,7 @@ class DefaultListenerHooks : public ListenerHooks {
   // ListenerHooks
   void onWorkerListenerAdded() override {}
   void onWorkerListenerRemoved() override {}
+  void onWorkersStarted() override {}
   void onRuntimeCreated() override {}
 };
 

source/server/listener_manager_impl.cc

@@ -884,7 +884,7 @@ bool ListenerManagerImpl::removeListenerInternal(const std::string& name,
   return true;
 }
 
-void ListenerManagerImpl::startWorkers(GuardDog& guard_dog) {
+void ListenerManagerImpl::startWorkers(GuardDog& guard_dog, std::function<void()> callback) {
   ENVOY_LOG(info, "all dependencies initialized. starting workers");
   ASSERT(!workers_started_);
   workers_started_ = true;
@@ -899,11 +899,13 @@ void ListenerManagerImpl::startWorkers(GuardDog& guard_dog) {
     ENVOY_LOG(debug, "starting worker {}", i);
     ASSERT(warming_listeners_.empty());
     for (const auto& listener : active_listeners_) {
-      addListenerToWorker(*worker, absl::nullopt, *listener, [this, listeners_pending_init]() {
-        if (--(*listeners_pending_init) == 0) {
-          stats_.workers_started_.set(1);
-        }
-      });
+      addListenerToWorker(*worker, absl::nullopt, *listener,
+                          [this, listeners_pending_init, callback]() {
+                            if (--(*listeners_pending_init) == 0) {
+                              stats_.workers_started_.set(1);
+                              callback();
+                            }
+                          });
     }
     worker->start(guard_dog);
     if (enable_dispatcher_stats_) {
@@ -913,6 +915,7 @@ void ListenerManagerImpl::startWorkers(GuardDog& guard_dog) {
   }
   if (active_listeners_.empty()) {
     stats_.workers_started_.set(1);
+    callback();
   }
 }
 

source/server/listener_manager_impl.h

@@ -193,7 +193,7 @@ class ListenerManagerImpl : public ListenerManager, Logger::Loggable<Logger::Id:
   listeners(ListenerState state = ListenerState::ACTIVE) override;
   uint64_t numConnections() const override;
   bool removeListener(const std::string& listener_name) override;
-  void startWorkers(GuardDog& guard_dog) override;
+  void startWorkers(GuardDog& guard_dog, std::function<void()> callback) override;
   void stopListeners(StopListenersType stop_listeners_type) override;
   void stopWorkers() override;
   void beginListenerUpdate() override { error_state_tracker_.clear(); }

source/server/server.cc

@@ -87,7 +87,7 @@ InstanceImpl::InstanceImpl(
                                                   : nullptr),
       grpc_context_(store.symbolTable()), http_context_(store.symbolTable()),
       router_context_(store.symbolTable()), process_context_(std::move(process_context)),
-      main_thread_id_(std::this_thread::get_id()), server_contexts_(*this) {
+      main_thread_id_(std::this_thread::get_id()), hooks_(hooks), server_contexts_(*this) {
   try {
     if (!options.logPath().empty()) {
       try {
@@ -609,15 +609,22 @@ void InstanceImpl::onRuntimeReady() {
 }
 
 void InstanceImpl::startWorkers() {
-  listener_manager_->startWorkers(*worker_guard_dog_);
-  initialization_timer_->complete();
-  // Update server stats as soon as initialization is done.
-  updateServerStats();
-  workers_started_ = true;
-  // At this point we are ready to take traffic and all listening ports are up. Notify our parent
-  // if applicable that they can stop listening and drain.
-  restarter_.drainParentListeners();
-  drain_manager_->startParentShutdownSequence();
+  // The callback will be called after workers are started.
+  listener_manager_->startWorkers(*worker_guard_dog_, [this]() {
+    if (isShutdown()) {
+      return;
+    }
+
+    initialization_timer_->complete();
+    // Update server stats as soon as initialization is done.
+    updateServerStats();
+    workers_started_ = true;
+    hooks_.onWorkersStarted();
+    // At this point we are ready to take traffic and all listening ports are up. Notify our
+    // parent if applicable that they can stop listening and drain.
+    restarter_.drainParentListeners();
+    drain_manager_->startParentShutdownSequence();
+  });
 }
 
 Runtime::LoaderPtr InstanceUtil::createRuntime(Instance& server,

source/server/server.h

@@ -365,6 +365,7 @@ class InstanceImpl final : Logger::Loggable<Logger::Id::main>,
   // initialization_time is a histogram for tracking the initialization time across hot restarts
   // whenever we have support for histogram merge across hot restarts.
   Stats::TimespanPtr initialization_timer_;
+  ListenerHooks& hooks_;
 
   ServerFactoryContextImpl server_contexts_;
 

test/integration/server.h

@@ -415,6 +415,7 @@ class IntegrationTestServer : public Logger::Loggable<Logger::Id::testing>,
     on_server_ready_cb_ = std::move(on_server_ready);
   }
   void onRuntimeCreated() override {}
+  void onWorkersStarted() override {}
 
   void start(const Network::Address::IpVersion version,
              std::function<void()> on_server_init_function, bool deterministic,

test/mocks/server/listener_manager.h

@@ -21,7 +21,7 @@ class MockListenerManager : public ListenerManager {
               (ListenerState state));
   MOCK_METHOD(uint64_t, numConnections, (), (const));
   MOCK_METHOD(bool, removeListener, (const std::string& listener_name));
-  MOCK_METHOD(void, startWorkers, (GuardDog & guard_dog));
+  MOCK_METHOD(void, startWorkers, (GuardDog & guard_dog, std::function<void()> callback));
   MOCK_METHOD(void, stopListeners, (StopListenersType listeners_type));
   MOCK_METHOD(void, stopWorkers, ());
   MOCK_METHOD(void, beginListenerUpdate, ());