add extra sanity check against depending on system time with isolation enabled

Author: RalfJung

src/concurrency/thread.rs

@@ -865,6 +865,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         callback: TimeoutCallback<'mir, 'tcx>,
     ) {
         let this = self.eval_context_mut();
+        if !this.machine.communicate() && matches!(call_time, Time::RealTime(..)) {
+            panic!("cannot have `RealTime` callback with isolation enabled!")
+        }
         this.machine.threads.register_timeout_callback(thread, call_time, callback);
     }
 

src/machine.rs

@@ -1018,6 +1018,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for Evaluator<'mir, 'tcx> {
         // These are our preemption points.
         ecx.maybe_preempt_active_thread();
 
+        // Make sure some time passes.
         ecx.machine.clock.tick();
 
         Ok(())