[Aggregator] Fix autocalibration scheduler

The list of knowns APs is now handled as a double-linked token ring
instead of a double-linked list.
The scheduler for autocalibration transmissions is now operational!

Delete the now-useless function move_ap_front(), which was not used
before anyway.

infrastructure-centred/owlps-aggregator/owlps-aggregator.h

@@ -108,7 +108,6 @@ void delete_old_aps(void) ;
 void delete_ap(ap_list *ap) ;
 void unlink_ap(ap_list *ap) ;
 void order_send(ap_list *ap) ;
-void move_ap_front(ap_list *ap) ;
 void free_ap_list(void) ;
 
 char* ip_bytes_to_string(unsigned char *ip_binary) ;

infrastructure-centred/owlps-aggregator/owlps-aggregatord.c

@@ -12,7 +12,7 @@
 char *program_name = NULL ;
 cfg_t *cfg = NULL ; // Configuration structure
 couple_list *couples = NULL ; // Computed data list
-ap_list *aps = NULL ;
+ap_list *token_aps = NULL ; // Token ring of the APs
 unsigned int nb_aps = 0 ;
 
 
@@ -733,14 +733,19 @@ void update_ap(unsigned char mac_addr_bytes[6], char ip_addr[16])
  */
 ap_list* find_ap(unsigned char mac_addr_bytes[6])
 {
-  ap_list *found = aps ;
+  ap_list *found ;
 
-  while (found != NULL)
+  if (token_aps == NULL)
+    return NULL ;
+
+  found = token_aps ;
+  do
     {
       if (mac_cmp(found->mac_addr_bytes, mac_addr_bytes))
         return found ;
       found = found->next ;
     }
+  while (found != token_aps) ;
 
   return NULL ;
 }
@@ -786,11 +791,20 @@ void update_ap_seen(ap_list *ap)
 void push_ap(ap_list *ap)
 {
   assert(ap) ;
-  ap->previous = NULL ;
-  ap->next = aps ;
-  if (aps != NULL)
-    aps->previous = ap ;
-  aps = ap ;
+
+  if (token_aps == NULL) // List does not exist yet
+    {
+      token_aps = ap ;
+      ap->next = ap ;
+      ap->previous = ap ;
+      return ;
+    }
+
+  ap->previous = token_aps->previous ;
+  ap->previous->next = ap ;
+  ap->next = token_aps ;
+  token_aps->previous = ap ;
+  token_aps = ap ;
 }
 
 
@@ -810,7 +824,10 @@ void monitor_aps()
       delete_old_aps() ;
 
       if (nb_aps > 1)
-        order_send(aps) ;
+        {
+          order_send(token_aps) ;
+          token_aps = token_aps->next ;
+        }
 
       usleep(cfg_getint(cfg, "ap_check_interval") * 1000) ;
     }
@@ -824,12 +841,16 @@ void monitor_aps()
 void delete_old_aps()
 {
   struct timeval now ;
+
+  if (token_aps == NULL)
+    return ;
+
   gettimeofday(&now, NULL) ;
 
-  while (aps != NULL)
-    if (sub_date(aps->last_seen, now) >
+  while (token_aps != token_aps->next)
+    if (sub_date(token_aps->last_seen, now) >
         (unsigned long) cfg_getint(cfg, "ap_keep_timeout") * 1000)
-      delete_ap(aps) ;
+      delete_ap(token_aps) ;
     else
       return ;
 }
@@ -857,14 +878,14 @@ void unlink_ap(ap_list *ap)
     *ap_previous = ap->previous,
     *ap_next = ap->next ;
 
-  if (ap_previous != NULL)
-    ap_previous->next = ap_next ;
+  assert(ap_previous) ;
+  assert(ap_next) ;
 
-  if (ap_next != NULL)
-    ap_next->previous = ap_previous ;
+  ap_previous->next = ap_next ;
+  ap_next->previous = ap_previous ;
 
-  if (ap == aps)
-    aps = ap_next ;
+  if (ap == token_aps)
+    token_aps = ap_next ;
 }
 
 
@@ -902,29 +923,28 @@ void order_send(ap_list *ap)
 }
 
 
-/*
- * Moves the given AP, existing in the AP list, in front of the list.
- */
-void move_ap_front(ap_list *ap)
-{
-  unlink_ap(ap) ;
-  push_ap(ap) ;
-}
-
-
 /*
  * Empties the AP list.
  */
 void free_ap_list()
 {
-  ap_list *ap_ptr = aps ;
+  ap_list *ap_ptr ;
 
-  while (ap_ptr != NULL)
+  if (token_aps == NULL)
+    return ;
+
+  ap_ptr = token_aps->next ;
+  assert(ap_ptr) ;
+
+  while (ap_ptr != token_aps)
     {
+      ap_list *ap_tmp = ap_ptr ;
       ap_ptr = ap_ptr->next ;
-      free(aps) ;
-      aps = ap_ptr ;
+      free(ap_tmp) ;
     }
+
+  free(token_aps) ;
+  token_aps = NULL ;
 }