avoid race between a scheduler starting up and an enclave trying to acquire.

Author: cmnrd

include/reactor-cpp/scheduler.hh

@@ -110,6 +110,10 @@ private:
 
   std::mutex scheduling_mutex_;
   std::condition_variable cv_schedule_;
+  // lock used to protect the scheduler from asynchronous requests (i.e. from
+  // enclaves pr federates). We hold the mutex from construction and release in
+  // start().
+  std::unique_lock<std::mutex> startup_lock_{scheduling_mutex_};
 
   std::shared_mutex mutex_event_queue_;
   std::map<Tag, ActionListPtr> event_queue_;

lib/scheduler.cc

@@ -214,6 +214,11 @@ void Scheduler::start() {
   set_ports_.resize(num_workers);
   triggered_reactions_.resize(num_workers);
 
+  // release the scheduling mutex, allowing other asynchronous processes (i.e.
+  // enclaves or federates) to access the event queue and the current logical
+  // time.
+  startup_lock_.unlock();
+
   // Initialize and start the workers. By resizing the workers vector first,
   // we make sure that there is sufficient space for all the workers and non of
   // them needs to be moved. This is important because a running worker may not