[wpiutil] Synchronization: fix shutdown use-after-free (#8213)

Also in ntcore, join the notifier thread on shutdown.
This prevents tsan from reporting it as a leaked thread.

ntcore/src/main/native/cpp/InstanceImpl.cpp

@@ -13,6 +13,7 @@ using namespace nt;
 std::atomic<int> InstanceImpl::s_default{-1};
 std::atomic<InstanceImpl*> InstanceImpl::s_instances[kNumInstances];
 wpi::mutex InstanceImpl::s_mutex;
+InstanceImpl::Cleanup InstanceImpl::s_cleanup;
 
 using namespace std::placeholders;
 

ntcore/src/main/native/cpp/InstanceImpl.h

@@ -75,6 +75,19 @@ class InstanceImpl {
   static std::atomic<InstanceImpl*> s_instances[kNumInstances];
   static wpi::mutex s_mutex;
 
+  struct Cleanup {
+    ~Cleanup() {
+      for (auto&& inst : s_instances) {
+        // don't actually destroy (due to undefined global destruction order),
+        // but stop all listener threads
+        if (auto i = inst.load()) {
+          i->listenerStorage.Reset();
+        }
+      }
+    }
+  };
+  static Cleanup s_cleanup;
+
   wpi::mutex m_mutex;
   std::shared_ptr<NetworkServer> m_networkServer;
   std::shared_ptr<INetworkClient> m_networkClient;

ntcore/src/main/native/cpp/ListenerStorage.cpp

@@ -355,9 +355,7 @@ void ListenerStorage::Reset() {
   m_valueListeners.clear();
   m_logListeners.clear();
   m_timeSyncListeners.clear();
-  if (m_thread) {
-    m_thread.Stop();
-  }
+  m_thread.Join();
 }
 
 std::vector<std::pair<NT_Listener, unsigned int>>