enb: fix stopping of input thread

since we've used a blocking read of stdin (with std::getline())
we had a race when the eNB was stopped and the user was still making
keyboard inputs. this is because the we didn't wait until the input
thread was terminated until we stopped the eNB.

we know use poll to query stdin (getline has no timeout mechanism).

srsenb/src/main.cc

@@ -19,6 +19,7 @@
  *
  */
 
+#include <poll.h>
 #include <pthread.h>
 #include <signal.h>
 #include <stdio.h>
@@ -401,43 +402,48 @@ static bool do_metrics = false;
 
 static void* input_loop(metrics_stdout* metrics, srsenb::enb_command_interface* control)
 {
-  string input_line;
+  struct pollfd pfd = {STDIN_FILENO, POLLIN, 0};
+  string        input_line;
   while (running) {
-    getline(cin, input_line);
-    if (cin.eof() || cin.bad()) {
-      cout << "Closing stdin thread." << endl;
-      break;
-    } else if (not input_line.empty()) {
-      vector<string> cmd;
-      srslte::string_parse_list(input_line, ' ', cmd);
-      if (cmd[0] == "t") {
-        do_metrics = !do_metrics;
-        if (do_metrics) {
-          cout << "Enter t to stop trace." << endl;
+    int ret = poll(&pfd, 1, 1000); // query stdin with a timeout of 1000ms
+    if (ret == 1) {
+      // there is user input to read
+      getline(cin, input_line);
+      if (cin.eof() || cin.bad()) {
+        cout << "Closing stdin thread." << endl;
+        break;
+      } else if (not input_line.empty()) {
+        vector<string> cmd;
+        srslte::string_parse_list(input_line, ' ', cmd);
+        if (cmd[0] == "t") {
+          do_metrics = !do_metrics;
+          if (do_metrics) {
+            cout << "Enter t to stop trace." << endl;
+          } else {
+            cout << "Enter t to restart trace." << endl;
+          }
+          metrics->toggle_print(do_metrics);
+        } else if (cmd[0] == "q") {
+          raise(SIGTERM);
+        } else if (cmd[0] == "cell_gain") {
+          if (cmd.size() != 3) {
+            cout << "Usage: " << cmd[0] << " [cell index] [gain in dB]" << endl;
+            continue;
+          }
+
+          // Parse command arguments
+          uint32_t cell_idx = srslte::string_cast<uint32_t>(cmd[1]);
+          float    gain_db  = srslte::string_cast<float>(cmd[2]);
+
+          // Set cell gain
+          control->cmd_cell_gain(cell_idx, gain_db);
         } else {
-          cout << "Enter t to restart trace." << endl;
+          cout << "Available commands: " << endl;
+          cout << "          t: starts console trace" << endl;
+          cout << "          q: quit srsenb" << endl;
+          cout << "  cell_gain: set relative cell gain" << endl;
+          cout << endl;
         }
-        metrics->toggle_print(do_metrics);
-      } else if (cmd[0] == "q") {
-        raise(SIGTERM);
-      } else if (cmd[0] == "cell_gain") {
-        if (cmd.size() != 3) {
-          cout << "Usage: " << cmd[0] << " [cell index] [gain in dB]" << endl;
-          continue;
-        }
-
-        // Parse command arguments
-        uint32_t cell_idx = srslte::string_cast<uint32_t>(cmd[1]);
-        float    gain_db  = srslte::string_cast<float>(cmd[2]);
-
-        // Set cell gain
-        control->cmd_cell_gain(cell_idx, gain_db);
-      } else {
-        cout << "Available commands: " << endl;
-        cout << "          t: starts console trace" << endl;
-        cout << "          q: quit srsenb" << endl;
-        cout << "  cell_gain: set relative cell gain" << endl;
-        cout << endl;
       }
     }
   }
@@ -504,9 +510,8 @@ int main(int argc, char* argv[])
   }
 
   // create input thread
-  thread input(&input_loop, &metrics_screen, (enb_command_interface*)enb.get());
+  std::thread input(&input_loop, &metrics_screen, (enb_command_interface*)enb.get());
 
-  bool signals_pregenerated = false;
   if (running) {
     if (args.gui.enable) {
       enb->start_plot();
@@ -521,8 +526,9 @@ int main(int argc, char* argv[])
         enb->print_pool();
       }
     }
-    usleep(10000);
+    std::this_thread::sleep_for(std::chrono::milliseconds(10));
   }
+  input.join();
   metricshub.stop();
   enb->stop();
   cout << "---  exiting  ---" << endl;