run the HTTP server on the event thread on Windows

src/HTTPServer.cc

@@ -162,12 +162,18 @@ const string& HTTPServer::get_url_param(
   return range.first->second;
 }
 
-HTTPServer::HTTPServer(shared_ptr<ServerState> state)
-    : state(state),
-      base(event_base_new(), event_base_free),
-      http(evhttp_new(this->base.get()), evhttp_free),
-      th(&HTTPServer::thread_fn, this) {
+HTTPServer::HTTPServer(shared_ptr<ServerState> state, shared_ptr<struct event_base> shared_base)
+    : state(state) {
+  if (!shared_base) {
+    this->base.reset(event_base_new(), event_base_free);
+  } else {
+    this->base = shared_base;
+  }
+  this->http.reset(evhttp_new(this->base.get()), evhttp_free);
   evhttp_set_gencb(this->http.get(), this->dispatch_handle_request, this);
+  if (!shared_base) {
+    this->th = thread(&HTTPServer::thread_fn, this);
+  }
 }
 
 void HTTPServer::listen(const string& socket_path) {

src/HTTPServer.hh

@@ -13,7 +13,8 @@
 
 class HTTPServer {
 public:
-  HTTPServer(std::shared_ptr<ServerState> state);
+  // shared_base should be null unless
+  HTTPServer(std::shared_ptr<ServerState> state, std::shared_ptr<struct event_base> shared_base);
   HTTPServer(const HTTPServer&) = delete;
   HTTPServer(HTTPServer&&) = delete;
   HTTPServer& operator=(const HTTPServer&) = delete;
@@ -57,7 +58,7 @@ protected:
   std::shared_ptr<ServerState> state;
   std::shared_ptr<struct event_base> base;
   std::shared_ptr<struct evhttp> http;
-  std::thread th;
+  std::thread th; // Not used on Windows
 
   std::unordered_set<std::shared_ptr<WebsocketClient>> rare_drop_subscribers;
 

src/Main.cc

@@ -3114,7 +3114,8 @@ Action a_run_server_replay_log(
 
         if (!state->http_addresses.empty() || !state->http_addresses.empty()) {
           config_log.info("Starting HTTP server");
-          state->http_server = make_shared<HTTPServer>(state);
+          shared_ptr<struct event_base> shared_base = IS_WINDOWS ? state->base : nullptr;
+          state->http_server = make_shared<HTTPServer>(state, shared_base);
           for (const auto& it : state->http_addresses) {
             auto netloc = phosg::parse_netloc(it);
             state->http_server->listen(netloc.first, netloc.second);