singleton manager: overload getTyped with non-constructing version (e…

…nvoyproxy#18362)

Signed-off-by: Jose Nino <[email protected]>

envoy/singleton/manager.h

@@ -73,6 +73,15 @@ class Manager {
     return std::dynamic_pointer_cast<T>(get(name, cb));
   }
 
+  /**
+   * This is a non-constructing getter. Use when the caller can deal with instances where
+   * the singleton being accessed may not have been constructed previously.
+   * @return InstancePtr the singleton. nullptr if the singleton does not exist.
+   */
+  template <class T> std::shared_ptr<T> getTyped(const std::string& name) {
+    return std::dynamic_pointer_cast<T>(get(name, [] { return nullptr; }));
+  }
+
   /**
    * Get a singleton and create it if it does not exist.
    * @param name supplies the singleton name. Must be registered via RegistrationImpl.

test/common/singleton/manager_impl_test.cc

@@ -42,6 +42,23 @@ TEST(SingletonManagerImplTest, Basic) {
   singleton.reset();
 }
 
+TEST(SingletonManagerImplTest, NonConstructingGetTyped) {
+  ManagerImpl manager(Thread::threadFactoryForTest());
+
+  // Access without first constructing should be null.
+  EXPECT_EQ(nullptr, manager.getTyped<TestSingleton>("test_singleton"));
+
+  std::shared_ptr<TestSingleton> singleton = std::make_shared<TestSingleton>();
+  // Use a construct on first use getter.
+  EXPECT_EQ(singleton, manager.get("test_singleton", [singleton] { return singleton; }));
+  // Now access should return the constructed singleton.
+  EXPECT_EQ(singleton, manager.getTyped<TestSingleton>("test_singleton"));
+  EXPECT_EQ(1UL, singleton.use_count());
+
+  EXPECT_CALL(*singleton, onDestroy());
+  singleton.reset();
+}
+
 } // namespace
 } // namespace Singleton
 } // namespace Envoy