move shell to separate thread

src/EventUtils.cc

@@ -0,0 +1,20 @@
+#include "EventUtils.hh"
+
+#include <event2/event.h>
+
+#include <deque>
+#include <functional>
+#include <memory>
+#include <stdexcept>
+
+static void dispatch_forward_to_event_thread(evutil_socket_t, short, void* ctx) {
+  auto* fn = reinterpret_cast<std::function<void()>*>(ctx);
+  (*fn)();
+  delete fn;
+}
+
+void forward_to_event_thread(std::shared_ptr<struct event_base> base, std::function<void()>&& fn) {
+  struct timeval tv = {0, 0};
+  std::function<void()>* new_fn = new std::function<void()>(std::move(fn));
+  event_base_once(base.get(), -1, EV_TIMEOUT, dispatch_forward_to_event_thread, new_fn, &tv);
+}