diff --git a/lib/base/registry.hpp b/lib/base/registry.hpp
index 5a8ac26f754..e2ef6784fb5 100644
--- a/lib/base/registry.hpp
+++ b/lib/base/registry.hpp
@@ -4,9 +4,13 @@
 #define REGISTRY_H
 
 #include "base/i2-base.hpp"
+#include "base/atomic.hpp"
+#include "base/exception.hpp"
 #include "base/string.hpp"
-#include <boost/signals2.hpp>
-#include <map>
+#include "base/singleton.hpp"
+#include <shared_mutex>
+#include <stdexcept>
+#include <unordered_map>
 #include <mutex>
 
 namespace icinga
@@ -17,22 +21,31 @@ namespace icinga
  *
  * @ingroup base
  */
-template<typename U, typename T>
+template<typename T>
 class Registry
 {
 public:
-	typedef std::map<String, T> ItemMap;
+	typedef std::unordered_map<String, T> ItemMap;
+
+	static Registry* GetInstance()
+	{
+		return Singleton<Registry>::GetInstance();
+	}
 
 	void Register(const String& name, const T& item)
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		std::unique_lock lock (m_Mutex);
+
+		if (m_Frozen) {
+			BOOST_THROW_EXCEPTION(std::logic_error("Registry is read-only and must not be modified."));
+		}
 
-		RegisterInternal(name, item, lock);
+		m_Items[name] = item;
 	}
 
 	T GetItem(const String& name) const
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		auto lock (ReadLockUnlessFrozen());
 
 		auto it = m_Items.find(name);
 
@@ -44,33 +57,36 @@ class Registry
 
 	ItemMap GetItems() const
 	{
-		std::unique_lock<std::mutex> lock(m_Mutex);
+		auto lock (ReadLockUnlessFrozen());
 
 		return m_Items; /* Makes a copy of the map. */
 	}
 
-	boost::signals2::signal<void (const String&, const T&)> OnRegistered;
-	boost::signals2::signal<void (const String&)> OnUnregistered;
-
-private:
-	mutable std::mutex m_Mutex;
-	typename Registry<U, T>::ItemMap m_Items;
-
-	void RegisterInternal(const String& name, const T& item, std::unique_lock<std::mutex>& lock)
+	/**
+	 * Freeze the registry, preventing further updates.
+	 *
+	 * This only prevents inserting, replacing or deleting values from the registry.
+	 * This operation has no effect on objects referenced by the values, these remain mutable if they were before.
+	 */
+	void Freeze()
 	{
-		bool old_item = false;
-
-		if (m_Items.erase(name) > 0)
-			old_item = true;
+		std::unique_lock lock (m_Mutex);
 
-		m_Items[name] = item;
+		m_Frozen.store(true);
+	}
 
-		lock.unlock();
+private:
+	mutable std::shared_mutex m_Mutex;
+	Atomic<bool> m_Frozen {false};
+	ItemMap m_Items;
 
-		if (old_item)
-			OnUnregistered(name);
+	std::shared_lock<std::shared_mutex> ReadLockUnlessFrozen() const
+	{
+		if (m_Frozen.load(std::memory_order_relaxed)) {
+			return {};
+		}
 
-		OnRegistered(name, item);
+		return std::shared_lock(m_Mutex);
 	}
 };
 
diff --git a/lib/db_ido/dbtype.cpp b/lib/db_ido/dbtype.cpp
index c5476b179d0..8006171ceb2 100644
--- a/lib/db_ido/dbtype.cpp
+++ b/lib/db_ido/dbtype.cpp
@@ -133,8 +133,3 @@ std::set<DbType::Ptr> DbType::GetAllTypes()
 
 	return result;
 }
-
-DbTypeRegistry *DbTypeRegistry::GetInstance()
-{
-	return Singleton<DbTypeRegistry>::GetInstance();
-}
diff --git a/lib/db_ido/dbtype.hpp b/lib/db_ido/dbtype.hpp
index c8ebc450409..b210aabb3f8 100644
--- a/lib/db_ido/dbtype.hpp
+++ b/lib/db_ido/dbtype.hpp
@@ -6,7 +6,6 @@
 #include "db_ido/i2-db_ido.hpp"
 #include "base/object.hpp"
 #include "base/registry.hpp"
-#include "base/singleton.hpp"
 #include <set>
 
 namespace icinga
@@ -57,17 +56,6 @@ class DbType final : public Object
 	ObjectMap m_Objects;
 };
 
-/**
- * A registry for DbType objects.
- *
- * @ingroup ido
- */
-class DbTypeRegistry : public Registry<DbTypeRegistry, DbType::Ptr>
-{
-public:
-	static DbTypeRegistry *GetInstance();
-};
-
 /**
  * Factory function for DbObject-based classes.
  *
diff --git a/lib/remote/apiaction.cpp b/lib/remote/apiaction.cpp
index ccde28190b8..ae31581d55e 100644
--- a/lib/remote/apiaction.cpp
+++ b/lib/remote/apiaction.cpp
@@ -1,10 +1,13 @@
 /* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
 
 #include "remote/apiaction.hpp"
-#include "base/singleton.hpp"
 
 using namespace icinga;
 
+INITIALIZE_ONCE_WITH_PRIORITY([]{
+	ApiActionRegistry::GetInstance()->Freeze();
+}, InitializePriority::FreezeNamespaces);
+
 ApiAction::ApiAction(std::vector<String> types, Callback action)
 	: m_Types(std::move(types)), m_Callback(std::move(action))
 { }
@@ -28,8 +31,3 @@ void ApiAction::Register(const String& name, const ApiAction::Ptr& action)
 {
 	ApiActionRegistry::GetInstance()->Register(name, action);
 }
-
-ApiActionRegistry *ApiActionRegistry::GetInstance()
-{
-	return Singleton<ApiActionRegistry>::GetInstance();
-}
diff --git a/lib/remote/apiaction.hpp b/lib/remote/apiaction.hpp
index 2bb98b1b6bb..8d803d04f07 100644
--- a/lib/remote/apiaction.hpp
+++ b/lib/remote/apiaction.hpp
@@ -45,11 +45,7 @@ class ApiAction final : public Object
  *
  * @ingroup remote
  */
-class ApiActionRegistry : public Registry<ApiActionRegistry, ApiAction::Ptr>
-{
-public:
-	static ApiActionRegistry *GetInstance();
-};
+using ApiActionRegistry = Registry<ApiAction::Ptr>;
 
 #define REGISTER_APIACTION(name, types, callback) \
 	INITIALIZE_ONCE([]() { \
diff --git a/lib/remote/apifunction.cpp b/lib/remote/apifunction.cpp
index f153dcb467a..563a5519fdf 100644
--- a/lib/remote/apifunction.cpp
+++ b/lib/remote/apifunction.cpp
@@ -1,10 +1,13 @@
 /* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
 
 #include "remote/apifunction.hpp"
-#include "base/singleton.hpp"
 
 using namespace icinga;
 
+INITIALIZE_ONCE_WITH_PRIORITY([]{
+	ApiFunctionRegistry::GetInstance()->Freeze();
+}, InitializePriority::FreezeNamespaces);
+
 ApiFunction::ApiFunction(const char* name, Callback function)
 	: m_Name(name), m_Callback(std::move(function))
 { }
@@ -23,8 +26,3 @@ void ApiFunction::Register(const String& name, const ApiFunction::Ptr& function)
 {
 	ApiFunctionRegistry::GetInstance()->Register(name, function);
 }
-
-ApiFunctionRegistry *ApiFunctionRegistry::GetInstance()
-{
-	return Singleton<ApiFunctionRegistry>::GetInstance();
-}
diff --git a/lib/remote/apifunction.hpp b/lib/remote/apifunction.hpp
index ea8b7cf1e46..2b0f3ed00fc 100644
--- a/lib/remote/apifunction.hpp
+++ b/lib/remote/apifunction.hpp
@@ -47,11 +47,7 @@ class ApiFunction final : public Object
  *
  * @ingroup base
  */
-class ApiFunctionRegistry : public Registry<ApiFunctionRegistry, ApiFunction::Ptr>
-{
-public:
-	static ApiFunctionRegistry *GetInstance();
-};
+using ApiFunctionRegistry = Registry<ApiFunction::Ptr>;
 
 #define REGISTER_APIFUNCTION(name, ns, callback) \
 	INITIALIZE_ONCE([]() { \
diff --git a/lib/remote/eventqueue.cpp b/lib/remote/eventqueue.cpp
index 819f95a6ae6..fa7ab0c160a 100644
--- a/lib/remote/eventqueue.cpp
+++ b/lib/remote/eventqueue.cpp
@@ -4,7 +4,6 @@
 #include "remote/eventqueue.hpp"
 #include "remote/filterutility.hpp"
 #include "base/io-engine.hpp"
-#include "base/singleton.hpp"
 #include "base/logger.hpp"
 #include "base/utility.hpp"
 #include <boost/asio/spawn.hpp>
@@ -125,11 +124,6 @@ void EventQueue::Register(const String& name, const EventQueue::Ptr& function)
 	EventQueueRegistry::GetInstance()->Register(name, function);
 }
 
-EventQueueRegistry *EventQueueRegistry::GetInstance()
-{
-	return Singleton<EventQueueRegistry>::GetInstance();
-}
-
 std::mutex EventsInbox::m_FiltersMutex;
 std::map<String, EventsInbox::Filter> EventsInbox::m_Filters ({{"", EventsInbox::Filter{1, Expression::Ptr()}}});
 
diff --git a/lib/remote/eventqueue.hpp b/lib/remote/eventqueue.hpp
index 833714f9d09..7b8b7e94147 100644
--- a/lib/remote/eventqueue.hpp
+++ b/lib/remote/eventqueue.hpp
@@ -59,11 +59,7 @@ class EventQueue final : public Object
  *
  * @ingroup base
  */
-class EventQueueRegistry : public Registry<EventQueueRegistry, EventQueue::Ptr>
-{
-public:
-	static EventQueueRegistry *GetInstance();
-};
+using EventQueueRegistry = Registry<EventQueue::Ptr>;
 
 enum class EventType : uint_fast8_t
 {