From 33b73193e8291fbd6b1bd95df5575a4dfac85c4e Mon Sep 17 00:00:00 2001
From: Robert Schmidt <robert.schmidt@eurecom.fr>
Date: Tue, 4 Aug 2020 19:25:47 +0200
Subject: [PATCH] FlexRAN timers: enable timer add/remove within timer event

A lock help during executing a timer event prevented such event from
creating/removing new timers due to a dead lock. This commit changes the
logic of the timing loop and adding/removing code such that this dead
lock does not happen.
---
 openair2/ENB_APP/flexran_agent_timer.c | 43 +++++++++++++++++---------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/openair2/ENB_APP/flexran_agent_timer.c b/openair2/ENB_APP/flexran_agent_timer.c
index 817e93dda8..238cd344f6 100644
--- a/openair2/ENB_APP/flexran_agent_timer.c
+++ b/openair2/ENB_APP/flexran_agent_timer.c
@@ -58,6 +58,11 @@ struct timesync {
 
   int                            timer_num;
   flexran_agent_timer_element_t *timer[MAX_NUM_TIMERS];
+
+  int                            add_num;
+  flexran_agent_timer_element_t *add_list[MAX_NUM_TIMERS];
+  int                            remove_num;
+  int                            remove_list[MAX_NUM_TIMERS];
   pthread_mutex_t                mutex_timer;
 
   int             exit;
@@ -76,8 +81,12 @@ err_code_t flexran_agent_timer_init(mid_t mod_id) {
   sync->current = 0;
   sync->next    = 0;
   sync->timer_num    = 0;
-  for (int i = 0; i < MAX_NUM_TIMERS; ++i)
+  sync->add_num = 0;
+  sync->remove_num = 0;
+  for (int i = 0; i < MAX_NUM_TIMERS; ++i) {
     sync->timer[i] = NULL;
+    sync->add_list[i] = NULL;
+  }
   pthread_mutex_init(&sync->mutex_timer, NULL);
   sync->exit   = 0;
 
@@ -170,12 +179,19 @@ void *flexran_agent_timer_thread(void *args) {
       break;
 
     pthread_mutex_lock(&sync->mutex_timer);
-    sync->current++;
-
-    if (sync->current < sync->next) {
-      pthread_mutex_unlock(&sync->mutex_timer);
-      continue;
+    for (int i = 0; i < sync->add_num; ++i) {
+      sync->timer[sync->timer_num] = sync->add_list[i];
+      sync->timer_num++;
     }
+    sync->add_num = 0;
+    for (int i = 0; i < sync->remove_num; ++i)
+      flexran_agent_timer_remove_internal(sync, sync->remove_list[i]);
+    sync->remove_num = 0;
+    pthread_mutex_unlock(&sync->mutex_timer);
+
+    sync->current++;
+    if (sync->current < sync->next)
+      continue;
 
     for (int i = 0; i < sync->timer_num; ++i) {
       flexran_agent_timer_element_t *t = sync->timer[i];
@@ -186,7 +202,6 @@ void *flexran_agent_timer_thread(void *args) {
       if (sync->next == sync->current || t->next < sync->next)
         sync->next = t->next;
     }
-    pthread_mutex_unlock(&sync->mutex_timer);
   }
   LOG_W(FLEXRAN_AGENT, "terminated timer thread\n");
   return NULL;
@@ -230,10 +245,10 @@ err_code_t flexran_agent_create_timer(mid_t    mod_id,
 
   struct timesync *sync = &timesync[mod_id];
   pthread_mutex_lock(&sync->mutex_timer);
-  if (sync->timer_num >= MAX_NUM_TIMERS) {
+  if (sync->timer_num + sync->add_num >= MAX_NUM_TIMERS) {
     pthread_mutex_unlock(&sync->mutex_timer);
     LOG_E(FLEXRAN_AGENT, "maximum number of timers (%d) reached while adding timer %d\n",
-          sync->timer_num, xid);
+          sync->timer_num + sync->add_num, xid);
     free(t);
     return TIMER_SETUP_FAILED;
   }
@@ -241,8 +256,8 @@ err_code_t flexran_agent_create_timer(mid_t    mod_id,
   t->next = sync->current + sf;
   if (sync->next <= sync->current || t->next < sync->next)
     sync->next = t->next;
-  sync->timer[sync->timer_num] = t;
-  sync->timer_num++;
+  sync->add_list[sync->add_num] = t;
+  sync->add_num++;
   pthread_mutex_unlock(&sync->mutex_timer);
   LOG_I(FLEXRAN_AGENT, "added new timer xid %d for agent %d\n", xid, mod_id);
   return 0;
@@ -250,15 +265,15 @@ err_code_t flexran_agent_create_timer(mid_t    mod_id,
 
 err_code_t flexran_agent_destroy_timer(mid_t mod_id, xid_t xid) {
   struct timesync *sync = &timesync[mod_id];
-  pthread_mutex_lock(&sync->mutex_timer);
   for (int i = 0; i < sync->timer_num; ++i) {
     if (sync->timer[i]->xid == xid) {
-      flexran_agent_timer_remove_internal(sync, i);
+      pthread_mutex_lock(&sync->mutex_timer);
+      sync->remove_list[sync->remove_num] = i;
+      sync->remove_num++;
       pthread_mutex_unlock(&sync->mutex_timer);
       return 0;
     }
   }
-  pthread_mutex_unlock(&sync->mutex_timer);
   LOG_E(FLEXRAN_AGENT, "could not find timer %d\n", xid);
   return TIMER_ELEMENT_NOT_FOUND;
 }