2 files changed, 218 insertions, 9 deletions

diff --git a/kernel/kapi/devices/interface_registry.cpp b/kernel/kapi/devices/interface_registry.cpp
index 2ec336ed..1d456b30 100644
--- a/kernel/kapi/devices/interface_registry.cpp
+++ b/kernel/kapi/devices/interface_registry.cpp
@@ -46,6 +46,8 @@ namespace kapi::devices
   auto interface_registry::do_publish(kstd::shared_ptr<device> device, kstd::string name, interface_id interface,
                                       void * implementation) -> kstd::result<void>
   {
+    // TODO: lock registry
+
     erase_if(m_entries, [interface](auto e) { return e.interface() == interface && !e.device(); });
 
     if (!device || !implementation || name.empty())
@@ -53,30 +55,87 @@ namespace kapi::devices
       return kstd::failure(make_error_code(kstd::errc::invalid_argument));
     }
 
-    auto published = std::ranges::any_of(m_entries, [&](auto const & entry) {
+    auto already_published = std::ranges::any_of(m_entries, [&](auto const & entry) {
       return entry.interface() == interface && entry.device().get() == device.get();
     });
 
-    if (published)
+    if (already_published)
     {
       return kstd::failure(make_error_code(kstd::errc::file_exists));
     }
 
-    m_entries.emplace_back(device, std::move(name), interface, implementation);
+    auto & published = m_entries.emplace_back(device, std::move(name), interface, implementation);
+
+    do_notify_published(interface, published);
 
     return kstd::success();
   }
 
-  auto interface_registry::unpublish(device const & device, interface_id interface) -> void
+  auto interface_registry::do_notify_published(interface_id interface, entry const & published) -> void
+  {
+    std::ranges::for_each(m_observers, [&](auto observer) {
+      if (auto locked_observer = observer.lock())
+      {
+        locked_observer->on_interface_published(interface, published);
+      }
+    });
+
+    std::ranges::for_each(m_static_observers,
+                          [&](auto observer) { observer->on_interface_published(interface, published); });
+  }
+
+  auto interface_registry::do_notify_withdrawn(interface_id interface, device const & device) -> void
+  {
+    std::ranges::for_each(m_observers, [&](auto observer) {
+      if (auto locked_observer = observer.lock())
+      {
+        locked_observer->on_interface_withdrawn(interface, const_cast<devices::device &>(device));
+      }
+    });
+
+    std::ranges::for_each(m_static_observers, [&](auto observer) {
+      observer->on_interface_withdrawn(interface, const_cast<devices::device &>(device));
+    });
+  }
+
+  auto interface_registry::withdraw(device const & device, interface_id interface) -> void
+  {
+    // TODO: lock registry
+
+    auto did_remove = erase_if(m_entries, [&](auto e) {
+                        auto locked_device = e.device();
+                        return e.interface() == interface && locked_device && locked_device.get() == &device;
+                      }) != 0;
+
+    if (did_remove)
+    {
+      do_notify_withdrawn(interface, device);
+    }
+  }
+
+  auto interface_registry::withdraw_all_for(device const & device) -> void
   {
+    // TODO: lock registry
+
+    auto withdrawn_interfaces = kstd::vector<interface_id>{};
+
     erase_if(m_entries, [&](auto e) {
       auto locked_device = e.device();
-      return e.interface() == interface && locked_device && locked_device.get() == &device;
+      auto do_erase = locked_device && locked_device.get() == &device;
+      if (do_erase)
+      {
+        withdrawn_interfaces.push_back(e.interface());
+      }
+      return do_erase;
     });
+
+    std::ranges::for_each(withdrawn_interfaces, [&](auto interface) { do_notify_withdrawn(interface, device); });
   }
 
   auto interface_registry::all(interface_id interface) const -> kstd::vector<entry>
   {
+    // TODO: lock registry
+
     auto filtered = m_entries;
     erase_if(filtered, [&](auto e) {
       auto locked_device = e.device();
@@ -87,6 +146,8 @@ namespace kapi::devices
 
   auto interface_registry::resolve(interface_id interface, std::string_view name) -> void *
   {
+    // TODO: lock registry
+
     auto found = std::ranges::find_if(m_entries, [&](auto e) { return e.name() == name && e.device(); });
 
     if (found == m_entries.cend())
@@ -103,6 +164,8 @@ namespace kapi::devices
 
   auto interface_registry::resolve(interface_id interface, device & device) -> void *
   {
+    // TODO: lock registry
+
     if (auto by_device = device.as(interface))
     {
       return by_device;
@@ -121,6 +184,29 @@ namespace kapi::devices
     return found->implementation();
   }
 
+  auto interface_registry::subscribe(kstd::weak_ptr<interface_registry_observer> observer) -> void
+  {
+    // TODO: lock registry
+
+    erase_if(m_observers, [](auto const & observer) { return observer.expired(); });
+    m_observers.push_back(observer);
+  }
+
+  auto interface_registry::subscribe(interface_registry_observer & observer) -> void
+  {
+    // TODO: lock registry
+
+    m_static_observers.push_back(&observer);
+  }
+
+  auto interface_registry::unsubscribe(interface_registry_observer & observer) -> void
+  {
+    // TODO: lock registry
+
+    erase_if(m_observers, [&](auto const & subscribed) { return subscribed.lock().get() == &observer; });
+    erase(m_static_observers, &observer);
+  }
+
 }  // namespace kapi::devices
 
 namespace kapi::test_support::devices
diff --git a/kernel/kapi/devices/interface_registry.tests.cpp b/kernel/kapi/devices/interface_registry.tests.cpp
index 4d2e2097..071b9a6d 100644
--- a/kernel/kapi/devices/interface_registry.tests.cpp
+++ b/kernel/kapi/devices/interface_registry.tests.cpp
@@ -4,6 +4,8 @@
 
 #include <catch2/catch_test_macros.hpp>
 
+#include <cstddef>
+
 namespace
 {
   struct probe_device
@@ -66,6 +68,44 @@ namespace
     const_device * m_const_device;
   };
 
+  struct counting_observer final : kapi::devices::interface_registry_observer
+  {
+    auto on_interface_published(kapi::devices::interface_id, kapi::devices::interface_registry::entry const &)
+        -> void override
+    {
+      ++published;
+    }
+
+    auto on_interface_withdrawn(kapi::devices::interface_id, kapi::devices::device &) -> void override
+    {
+      ++withdrawn;
+    }
+
+    std::size_t published{};
+    std::size_t withdrawn{};
+  };
+
+  struct evil_observer final : kapi::devices::interface_registry_observer
+  {
+    explicit evil_observer(kstd::shared_ptr<counting_observer> & victim)
+        : m_victim{victim}
+    {}
+
+    auto on_interface_published(kapi::devices::interface_id, kapi::devices::interface_registry::entry const &)
+        -> void override
+    {
+      m_victim.reset();
+    }
+
+    auto on_interface_withdrawn(kapi::devices::interface_id, kapi::devices::device &) -> void override
+    {
+      m_victim.reset();
+    }
+
+  private:
+    kstd::shared_ptr<counting_observer> & m_victim;  // NOLINT
+  };
+
 }  // namespace
 
 SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]")
@@ -138,7 +178,7 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
         }
       }
 
-      THEN("find finds the published capability by name")
+      THEN("resolve finds the published capability by name")
       {
         REQUIRE(registry.resolve<probe_device>("probe0"));
       }
@@ -153,14 +193,14 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
         REQUIRE_FALSE(registry.resolve<unimplemented_device>("probe0"));
       }
 
-      THEN("find for an unpublished device does not find a device")
+      THEN("resolve for an unpublished device does not find a device")
       {
         REQUIRE_FALSE(registry.resolve<probe_device>("probe1"));
       }
 
       THEN("withdrawing an interface for a device removes it from the registry")
       {
-        registry.unpublish(*device, probe_device::id);
+        registry.withdraw(*device, probe_device::id);
         REQUIRE_FALSE(registry.resolve<probe_device>("probe0"));
       }
     }
@@ -175,7 +215,7 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
         REQUIRE(registry.all(probe_device::id).empty());
       }
 
-      THEN("find() no longer finds it")
+      THEN("resolve() no longer finds it")
       {
         REQUIRE_FALSE(registry.resolve<probe_device>("probe0"));
       }
@@ -204,3 +244,86 @@ SCENARIO("Publishing and finding a device", "[kapi][devices][interface_registry]
     }
   }
 }
+
+SCENARIO("Interface registry notifies subscribers", "[kapi][devices][interface_registry]")
+{
+  GIVEN("a device and a subscribed observer")
+  {
+    auto registry = kapi::devices::interface_registry{};
+    auto free_standing_interface = const_device{};
+    auto device = kstd::make_shared<test_device>(128, free_standing_interface);
+    auto observer = kstd::make_shared<counting_observer>();
+
+    registry.subscribe(observer);
+
+    WHEN("an interface is published for the device")
+    {
+      CHECK(registry.publish(device, "probe0", device->as<probe_device>()));
+
+      THEN("the observer is notified exactly once")
+      {
+        REQUIRE(observer->published == 1);
+        REQUIRE(observer->withdrawn == 0);
+      }
+    }
+
+    WHEN("an interface is published and then withdrawn")
+    {
+      CHECK(registry.publish(device, "probe0", device->as<probe_device>()));
+      registry.withdraw(*device, probe_device::id);
+
+      THEN("the observer is notified of both exactly one")
+      {
+        REQUIRE(observer->published == 1);
+        REQUIRE(observer->withdrawn == 1);
+      }
+    }
+
+    WHEN("the observer is destroyed before anything is published")
+    {
+      observer.reset();
+
+      THEN("publishing afterward does not crash")
+      {
+        REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+      }
+    }
+
+    WHEN("the observer unsubscribes before anything is published")
+    {
+      registry.unsubscribe(*observer);
+
+      THEN("publishing afterward does not crash")
+      {
+        REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+      }
+
+      THEN("the subscriber is not notified")
+      {
+        REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+        REQUIRE_NOTHROW(registry.withdraw(*device, probe_device::id));
+        REQUIRE(observer->published == 0);
+        REQUIRE(observer->withdrawn == 0);
+      }
+    }
+  }
+
+  GIVEN("two subscriber, the first destroying the second")
+  {
+    auto registry = kapi::devices::interface_registry{};
+    auto free_standing_interface = const_device{};
+    auto device = kstd::make_shared<test_device>(128, free_standing_interface);
+
+    auto second = kstd::make_shared<counting_observer>();
+    auto first = kstd::make_shared<evil_observer>(second);
+
+    registry.subscribe(first);
+    registry.subscribe(second);
+
+    THEN("publishing an interface does not crash")
+    {
+      REQUIRE_NOTHROW(registry.publish(device, "probe0", device->as<probe_device>()));
+      REQUIRE(second == nullptr);
+    }
+  }
+}
\ No newline at end of file