- task = MSG_comm_get_task(node->comm_receive);
- task_data_t ans_data = MSG_task_get_data(task);
-
- if (ans_data->type != TASK_FIND_SUCCESSOR_ANSWER) {
- handle_task(node, task);
+ msg_task_t task_received = MSG_comm_get_task(node->comm_receive);
+ XBT_DEBUG("Received a task (%p)", task_received);
+ task_data_t ans_data = MSG_task_get_data(task_received);
+
+ // Once upon a time, our code assumed that here, task_received != task_sent all the time
+ //
+ // This assumption is wrong (as messages from differing round can interleave), leading to a bug in our code.
+ // We failed to find this bug directly, as it only occured on large platforms, leading to hardly usable traces.
+ // Instead, we used the model-checker to track down the issue by adding the following test here in the code:
+ // if (MC_is_active()) {
+ // MC_assert(task_received == task_sent);
+ // }
+ // That explained the bug in a snap, with a very cool example and everything.
+ //
+ // This MC_assert is now desactivated as the case is now properly handled in our code and we don't want the
+ // MC to fail any further under that condition, but this comment is here to as a memorial for this first
+ // brillant victory of the model-checking in the SimGrid community :)
+
+ if (task_received != task_sent) {
+ // this is not the expected answer
+ MSG_comm_destroy(node->comm_receive);
+ node->comm_receive = NULL;
+ handle_task(node, task_received);