Add ability to end startCompetition() main loop (#2032)

This is useful for both cleanly exiting from simulation and for unit testing
at a framework level.

This change required removing move constructor/assignment from IterativeRobot.

wpilibc/src/main/native/include/frc/RobotBase.h

@@ -7,9 +7,12 @@
 
 #pragma once
 
+#include <chrono>
 #include <thread>
 
 #include <hal/Main.h>
+#include <wpi/condition_variable.h>
+#include <wpi/mutex.h>
 #include <wpi/raw_ostream.h>
 
 #include "frc/Base.h"
@@ -23,9 +26,13 @@ int RunHALInitialization();
 namespace impl {
 
 template <class Robot>
-void RunRobot() {
-  static Robot robot;
-  robot.StartCompetition();
+void RunRobot(wpi::mutex& m, Robot** robot) {
+  static Robot theRobot;
+  {
+    std::scoped_lock lock{m};
+    *robot = &theRobot;
+  }
+  theRobot.StartCompetition();
 }
 
 }  // namespace impl
@@ -36,20 +43,50 @@ int StartRobot() {
   if (halInit != 0) {
     return halInit;
   }
+
+  static wpi::mutex m;
+  static wpi::condition_variable cv;
+  static Robot* robot = nullptr;
+  static bool exited = false;
+
   if (HAL_HasMain()) {
-    std::thread([] {
+    std::thread thr([] {
       try {
-        impl::RunRobot<Robot>();
+        impl::RunRobot<Robot>(m, &robot);
       } catch (...) {
         HAL_ExitMain();
+        {
+          std::scoped_lock lock{m};
+          robot = nullptr;
+          exited = true;
+        }
+        cv.notify_all();
         throw;
       }
+
       HAL_ExitMain();
-    })
-        .detach();
+      {
+        std::scoped_lock lock{m};
+        robot = nullptr;
+        exited = true;
+      }
+      cv.notify_all();
+    });
+
     HAL_RunMain();
+
+    // signal loop to exit
+    if (robot) robot->EndCompetition();
+
+    // prefer to join, but detach to exit if it doesn't exit in a timely manner
+    using namespace std::chrono_literals;
+    std::unique_lock lock{m};
+    if (cv.wait_for(lock, 1s, [] { return exited; }))
+      thr.join();
+    else
+      thr.detach();
   } else {
-    impl::RunRobot<Robot>();
+    impl::RunRobot<Robot>(m, &robot);
   }
 
   return 0;
@@ -127,6 +164,8 @@ class RobotBase {
 
   virtual void StartCompetition() = 0;
 
+  virtual void EndCompetition() = 0;
+
   static constexpr bool IsReal() {
 #ifdef __FRC_ROBORIO__
     return true;