check & join supervisor thread when terminating student program

src/command/common.rs

@@ -43,8 +43,13 @@ pub fn terminate_student_program(exec: &mut SyncExecutionContext) -> CommandResu
 
     for _ in 0..20 {
         std::thread::sleep(Duration::from_millis(100)); // Sensible amount?
-        let con = exec.lock().unwrap();
+        let mut con = exec.lock().unwrap();
         if con.thread_handle.as_ref().unwrap().is_finished() {
+            con.thread_handle
+                .take()
+                .unwrap()
+                .join()
+                .or(Err(CommandError::NonRecoverable("Supervisor thread panicked".into())))?;
             return Ok(());
         }
     }

src/command/execute_program.rs

@@ -34,10 +34,7 @@ pub fn execute_program(
     // WATCHDOG THREAD
     let mut wd_context = exec.clone();
     let wd_handle = std::thread::spawn(move || {
-        let exit_code = match supervise_process(student_process, timeout, &mut wd_context) {
-            Ok(code) => code,
-            Err(()) => 255,
-        };
+        let exit_code = supervise_process(student_process, timeout, &mut wd_context).unwrap_or(255);
 
         log::info!("Program {}:{} finished with {}", program_id, timestamp, exit_code);
         let sid = ProgramStatus { program_id, timestamp, exit_code };

src/command/execution_context.rs

@@ -46,7 +46,7 @@ impl ExecutionContext {
     }
 
     pub fn is_student_program_running(&self) -> bool {
-        self.running_flag
+        self.thread_handle.is_some()
     }
 
     pub fn has_data_ready(&self) -> bool {