Fix SharedFuture from async_send_request never becomes valid (ros2#2044…

…) (ros2#2076) (#6)

(cherry picked from commit 66b1944)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Co-authored-by: Lei Liu <64953129+llapx@users.noreply.github.com>

rclcpp/include/rclcpp/client.hpp

@@ -792,16 +792,14 @@ class Client : public ClientBase
   async_send_request_impl(const Request & request, CallbackInfoVariant value)
   {
     int64_t sequence_number;
+    std::lock_guard<std::mutex> lock(pending_requests_mutex_);
     rcl_ret_t ret = rcl_send_request(get_client_handle().get(), &request, &sequence_number);
     if (RCL_RET_OK != ret) {
       rclcpp::exceptions::throw_from_rcl_error(ret, "failed to send request");
     }
-    {
-      std::lock_guard<std::mutex> lock(pending_requests_mutex_);
-      pending_requests_.try_emplace(
-        sequence_number,
-        std::make_pair(std::chrono::system_clock::now(), std::move(value)));
-    }
+    pending_requests_.try_emplace(
+      sequence_number,
+      std::make_pair(std::chrono::system_clock::now(), std::move(value)));
     return sequence_number;
   }