plugin: initialize factor weights on plugin load

Problem: The weight of each factor is checked every time the priority of
a job is calculated. It would be cleaner to put this check somewhere
else so it does not need to be repeated.

Create defaults for the weights of each factor used in the priority
calculation of a job. Initialize each weight when the plugin is loaded.
In the callback for conf.update, check to see if these weights have been
configured; if not, continue to use the defaults defined at the top of
the file.

src/plugins/mf_priority.cpp

@@ -38,6 +38,11 @@ extern "C" {
 // flux-accounting
 #define BANK_INFO_MISSING 999
 
+// default weights for each factor in the priority calculation for a job
+#define DEFAULT_FSHARE_WEIGHT 100000
+#define DEFAULT_QUEUE_WEIGHT 10000
+#define DEFAULT_AGE_WEIGHT 1000
+
 std::map<int, std::map<std::string, Association>> users;
 std::map<std::string, Queue> queues;
 std::map<int, std::string> users_def_bank;
@@ -75,11 +80,6 @@ int64_t priority_calculation (flux_plugin_t *p,
     fshare_weight = priority_weights["fairshare"];
     queue_weight = priority_weights["queue"];
 
-    // check values of priority factor weights; if not configured,
-    // these will be set to -1, so just use default weights
-    if (fshare_weight == -1) fshare_weight = 100000;
-    if (queue_weight == -1) queue_weight = 10000;
-
     if (urgency == FLUX_JOB_URGENCY_HOLD)
         return FLUX_JOB_PRIORITY_MIN;
 
@@ -201,8 +201,8 @@ static int conf_update_cb (flux_plugin_t *p,
     }
 
     // assign unpacked weights into priority_weights map
-    priority_weights["fairshare"] = fshare_weight;
-    priority_weights["queue"] = queue_weight;
+    if (fshare_weight != -1) priority_weights["fairshare"] = fshare_weight;
+    if (queue_weight != -1) priority_weights["queue"] = queue_weight;
 
     return 0;
 }
@@ -1108,6 +1108,11 @@ extern "C" int flux_plugin_init (flux_plugin_t *p)
         < 0)
         return -1;
 
+    // initialize the weights of the priority factors with default values
+    priority_weights["fairshare"] = DEFAULT_FSHARE_WEIGHT;
+    priority_weights["queue"] = DEFAULT_QUEUE_WEIGHT;
+    priority_weights["age"] = DEFAULT_AGE_WEIGHT;
+
     return 0;
 }