AP_HAL_Linux: allow PollerThread to stop

libraries/AP_HAL_Linux/PollerThread.cpp

@@ -140,10 +140,25 @@ void PollerThread::mainloop()
         return;
     }
 
-    while (true) {
+    while (!_should_exit) {
         _poller.poll();
         _cleanup_timers();
     }
+
+    _started = false;
+    _should_exit = false;
+}
+
+bool PollerThread::stop()
+{
+    if (!is_started()) {
+        return false;
+    }
+
+    _should_exit = true;
+    _poller.wakeup();
+
+    return true;
 }
 
 }

libraries/AP_HAL_Linux/PollerThread.h

@@ -72,6 +72,8 @@ public:
 
     void mainloop();
 
+    bool stop() override;
+
 protected:
     void _cleanup_timers();
 

libraries/AP_HAL_Linux/Thread.h

@@ -45,6 +45,8 @@ public:
 
     bool set_stack_size(size_t stack_size);
 
+    virtual bool stop() { return false; }
+
 protected:
     static void *_run_trampoline(void *arg);
 
@@ -59,6 +61,7 @@ protected:
 
     task_t _task;
     bool _started = false;
+    bool _should_exit = false;
     pthread_t _ctx = 0;
 
     struct stack_debug {