[wpinet] Move network portions of wpiutil into new wpinet library (#4077)

wpinet/src/main/native/macOS/ResolverThread.h

@@ -0,0 +1,46 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <netinet/in.h>
+#include <poll.h>
+
+#include <atomic>
+#include <memory>
+#include <thread>
+#include <utility>
+#include <vector>
+
+#include <wpi/Synchronization.h>
+#include <wpi/mutex.h>
+
+#include "dns_sd.h"
+
+namespace wpi {
+class ResolverThread {
+ private:
+  struct private_init {};
+
+ public:
+  explicit ResolverThread(const private_init&);
+  ~ResolverThread() noexcept;
+
+  void AddServiceRef(DNSServiceRef serviceRef, dnssd_sock_t socket);
+  void RemoveServiceRefInThread(DNSServiceRef serviceRef);
+  WPI_EventHandle RemoveServiceRefOutsideThread(DNSServiceRef serviceRef);
+
+  static std::shared_ptr<ResolverThread> Get();
+
+ private:
+  void ThreadMain();
+  bool CleanupRefs();
+
+  wpi::mutex serviceRefMutex;
+  std::vector<std::pair<DNSServiceRef, WPI_EventHandle>> serviceRefsToRemove;
+  std::vector<std::pair<DNSServiceRef, dnssd_sock_t>> serviceRefs;
+  std::thread thread;
+  std::atomic_bool running;
+};
+}  // namespace wpi