From: Martin Quinson <martin.quinson@loria.fr>
Date: Mon, 10 Dec 2012 11:27:36 +0000 (+0100)
Subject: document an ugly pimple in the code that were added for autorestart to work
X-Git-Tag: v3_9_rc1~86^2~148
X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/commitdiff_plain/3afb7fcd5847dbd9cf2005e28d45eadcf96a399b

document an ugly pimple in the code that were added for autorestart to work
---

diff --git a/src/surf/surf.c b/src/surf/surf.c
index 5309c43bb7..fbf2ae3c71 100644
--- a/src/surf/surf.c
+++ b/src/surf/surf.c
@@ -608,11 +608,11 @@ double surf_solve(double max_date)
         min = MAX(next_event_date - NOW, min);
       }
 
-      XBT_DEBUG("Run for NS3 at most %f", min);
+      XBT_DEBUG("Run for network at most %f", min);
       // run until min or next flow
       model_next_action_end = surf_network_model->model_private->share_resources(min);
 
-      XBT_DEBUG("Min for NS3 : %f", model_next_action_end);
+      XBT_DEBUG("Min for network : %f", model_next_action_end);
       if(model_next_action_end>=0.0)
         min = model_next_action_end;
     }
@@ -738,6 +738,33 @@ void surf_set_nthreads(int nthreads) {
   surf_nthreads = nthreads;
 }
 
+/* This function is a pimple that we ought to fix. But it won't be easy.
+ *
+ * The surf_solve() function does properly return the set of actions that changed.
+ * Instead, each model change a global data, and then the caller of surf_solve must
+ * pick into these sets of action_failed and action_done.
+ *
+ * This was not clean but ok as long as we didn't had to restart the processes when the resource comes back up.
+ * We worked by putting sentinel actions on every resources we are interested in,
+ * so that surf informs us if/when the corresponding resource fails.
+ *
+ * But this does not work to get Simix informed of when a resource comes back up, and this is where this pimple comes.
+ * We have a set of resources that are currently down and for which simix needs to know when it comes back up.
+ * And the current function is called *at every simulation step* to sweep over that set, searching for a resource
+ * that was turned back up in the meanwhile. This is UGLY and slow.
+ *
+ * The proper solution would be to not rely on globals for the action_failed and action_done swags.
+ * They must be passed as parameter by the caller (the handling of these actions in simix may let you
+ * think that these two sets can be merged, but their handling in SimDag induce the contrary unless this
+ * simdag code can check by itself whether the action is done of failed -- seems very doable, but yet more
+ * cleanup to do).
+ *
+ * Once surf_solve() is passed the set of actions that changed, you want to add a new set of resources back up
+ * as parameter to this function. You also want to add a boolean field "restart_watched" to each resource, and
+ * make sure that whenever a resource with this field enabled comes back up, it's added to that set so that Simix
+ * sees it and react accordingly. This would kill that need for surf to call simix.
+ *
+ */
 void surf_watched_hosts(void)
 {
   char *key;