Fix rtde client shutdown (UniversalRobots#474)

Destroying an RTDE client with a lost (but not shutdown) connection can
hang. This can happen for example due to a server crash or a lost
network / plugged cable.

This commit adds a test case for that where the fake RTDE server simply
stops sending data.

Pausing an active RTDE communication before disconnecting shouldn't be
strictly necessary and as far as I remember was added as a workaround to
mitigate callback issues. These should not be present since we
refactored the RTDEClient to no longer use the pipeline (which it never
fully used, anyway).

Thus, this structure should allow a cleaner implementation with a
clearer logic flow.

Author: urfeex

src/rtde/rtde_client.cpp

@@ -91,8 +91,6 @@ RTDEClient::~RTDEClient()
   {
     reconnecting_thread_.join();
   }
-  prod_->stopProducer();
-  stopBackgroundRead();
   disconnect();
 }
 
@@ -510,14 +508,6 @@ bool RTDEClient::setupInputs()
 
 void RTDEClient::disconnect()
 {
-  // If communication is started it should be paused before disconnecting
-  if (client_state_ == ClientState::RUNNING)
-  {
-    pause();
-  }
-  if (client_state_ >= ClientState::INITIALIZING)
-  {
-  }
   if (client_state_ > ClientState::UNINITIALIZED)
   {
     stream_.disconnect();

tests/test_rtde_client.cpp

@@ -43,6 +43,7 @@
 
 #include "fake_rtde_server.h"
 #include "ur_client_library/helpers.h"
+#include "ur_client_library/log.h"
 
 using namespace urcl;
 
@@ -419,6 +420,33 @@ TEST_F(RTDEClientTest, get_data_package_fake_server)
   client_.reset();
 }
 
+TEST_F(RTDEClientTest, destroy_client_after_server_stops_sending)
+{
+  auto fake_rtde_server = std::make_unique<RTDEServer>(g_FAKE_RTDE_PORT);
+  fake_rtde_server->setStartTime(std::chrono::steady_clock::now() - std::chrono::seconds(42));
+  client_.reset(new rtde_interface::RTDEClient("localhost", notifier_, resources_output_recipe_,
+                                               resources_input_recipe_, 100, false, g_FAKE_RTDE_PORT));
+  client_->init();
+  client_->start();
+
+  URCL_LOG_INFO("Receiving data package from fake server to verify that connection is working.");
+
+  const std::chrono::milliseconds read_timeout{ 100 };
+  auto data_pkg = rtde_interface::DataPackage(client_->getOutputRecipe());
+  ASSERT_TRUE(client_->getDataPackage(data_pkg, read_timeout));
+
+  double timestamp = 0.0;
+  EXPECT_TRUE(data_pkg.getData("timestamp", timestamp));
+  EXPECT_GT(timestamp, 0.0);
+
+  URCL_LOG_INFO("Stopping fake server from sending data packages.");
+  fake_rtde_server->stopSendingDataPackages();
+  std::this_thread::sleep_for(std::chrono::milliseconds(50));
+
+  URCL_LOG_INFO("Destroying client while no more data packages are received from the server.");
+  client_.reset();
+}
+
 TEST_F(RTDEClientTest, reconnect_fake_server_background_read)
 {
   auto fake_rtde_server = std::make_unique<RTDEServer>(g_FAKE_RTDE_PORT);