Ensure ASIO thread cannot be stopped prematurely

src/libponyrt/asio/asio.c

@@ -59,7 +59,7 @@ bool ponyint_asio_start()
 
 bool ponyint_asio_stop()
 {
-  if(atomic_load_explicit(&running_base.noisy_count, memory_order_relaxed) > 0)
+  if(!ponyint_asio_stoppable())
     return false;
 
   if(running_base.backend != NULL)
@@ -74,6 +74,12 @@ bool ponyint_asio_stop()
   return true;
 }
 
+bool ponyint_asio_stoppable()
+{
+  // can only stop if we have no noisy actors
+  return atomic_load_explicit(&running_base.noisy_count, memory_order_relaxed) == 0;
+}
+
 uint64_t ponyint_asio_noisy_add()
 {
   return atomic_fetch_add_explicit(&running_base.noisy_count, 1, memory_order_relaxed);

src/libponyrt/asio/asio.h

@@ -83,6 +83,13 @@ uint32_t ponyint_asio_get_cpu();
  */
 bool ponyint_asio_stop();
 
+/** Checks if it is safe to stop the asynchronous event mechanism.
+ *
+ * Stopping an event mechanism is only possible if there are no pending "noisy"
+ * subscriptions.
+ */
+bool ponyint_asio_stoppable();
+
 /** Add a noisy event subscription.
  */
 uint64_t ponyint_asio_noisy_add();

src/libponyrt/sched/scheduler.c

@@ -212,18 +212,6 @@ static void handle_sched_block(scheduler_t* sched)
 // handle SCHED_UNBLOCK message
 static void handle_sched_unblock(scheduler_t* sched)
 {
-  // if the ASIO thread has already been stopped
-  if (sched->asio_stopped)
-  {
-    // restart the ASIO thread
-    ponyint_asio_init(asio_cpu);
-    sched->asio_stopped = !ponyint_asio_start();
-  }
-
-  // make sure asio hasn't already been stopped or else runtime is in
-  // an invalid state without the ASIO thread running
-  pony_assert(!sched->asio_stopped);
-
   // Cancel all acks and increment the ack token, so that any pending
   // acks in the queue will be dropped when they are received.
   sched->block_count--;
@@ -328,21 +316,26 @@ static bool quiescent(scheduler_t* sched, uint64_t tsc, uint64_t tsc2)
 
   if(sched->ack_count >= current_active_scheduler_count)
   {
-    if(sched->asio_stopped)
+    if(sched->asio_stoppable && ponyint_asio_stop())
     {
+      // successfully stopped ASIO thread
+      // tell all scheduler threads to terminate
       send_msg_all(sched->index, SCHED_TERMINATE, 0);
 
       wake_suspended_threads(sched->index);
 
       sched->ack_token++;
       sched->ack_count = 0;
-    } else if(ponyint_asio_stop()) {
-      sched->asio_stopped = true;
+    } else if(ponyint_asio_stoppable()) {
+      sched->asio_stoppable = true;
       sched->ack_token++;
       sched->ack_count = 0;
 
       // Run another CNF/ACK cycle.
       send_msg_all_active(sched->index, SCHED_CNF, sched->ack_token);
+    } else {
+      // ASIO is not stoppable
+      sched->asio_stoppable = false;
     }
   }
 

src/libponyrt/sched/scheduler.h

@@ -56,7 +56,7 @@ struct scheduler_t
   uint32_t cpu;
   uint32_t node;
   bool terminate;
-  bool asio_stopped;
+  bool asio_stoppable;
   bool asio_noisy;
   pony_signal_event_t sleep_object;