X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/0821eaf865ee5431f938481ede3c2e77ef095f65..e99158dd85fe789ea5e1a40c29f196fa6c715bcf:/examples/msg/chord/chord.c

diff --git a/examples/msg/chord/chord.c b/examples/msg/chord/chord.c
index b11287434b..ef8324c8e3 100644
--- a/examples/msg/chord/chord.c
+++ b/examples/msg/chord/chord.c
@@ -1,27 +1,28 @@
-
-/* Copyright (c) 2010. The SimGrid Team.
+/* Copyright (c) 2010-2015. The SimGrid Team.
  * All rights reserved.                                                     */
 
 /* This program is free software; you can redistribute it and/or modify it
  * under the terms of the license (GNU LGPL) which comes with this package. */
 
 #include <stdio.h>
-#include "msg/msg.h"
+#include "simgrid/msg.h"
 #include "xbt/log.h"
 #include "xbt/asserts.h"
 #include "simgrid/modelchecker.h"
+#include <xbt/RngStream.h>
+#include "src/mc/mc_replay.h" // FIXME: this is an internal header
 
 /** @addtogroup MSG_examples
  *
  *  - <b>chord/chord.c: Classical Chord P2P protocol</b>
  *    This example implements the well known Chord P2P protocol. Its
  *    main advantage is that it constitute a fully working non-trivial
- *    example. In addition, its implementation is rather efficient, as 
+ *    example. In addition, its implementation is rather efficient, as
  *    demonstrated in http://hal.inria.fr/inria-00602216/
  */
 
- 
- XBT_LOG_NEW_DEFAULT_CATEGORY(msg_chord,
+
+XBT_LOG_NEW_DEFAULT_CATEGORY(msg_chord,
                              "Messages specific for this msg example");
 
 #define COMM_SIZE 10
@@ -37,20 +38,22 @@ static int periodic_fix_fingers_delay = 120;
 static int periodic_check_predecessor_delay = 120;
 static int periodic_lookup_delay = 10;
 
+static const double sleep_delay = 4.9999;
+
 extern long int smx_total_comms;
 
-/**
+/*
  * Finger element.
  */
-typedef struct finger {
+typedef struct s_finger {
   int id;
   char mailbox[MAILBOX_NAME_SIZE]; // string representation of the id
 } s_finger_t, *finger_t;
 
-/**
+/*
  * Node data.
  */
-typedef struct node {
+typedef struct s_node {
   int id;                                 // my id
   char mailbox[MAILBOX_NAME_SIZE];        // my mailbox name (string representation of the id)
   s_finger_t *fingers;                    // finger table, of size nb_bits (fingers[0] is my successor)
@@ -59,6 +62,7 @@ typedef struct node {
   int next_finger_to_fix;                 // index of the next finger to fix in fix_fingers()
   msg_comm_t comm_receive;                // current communication to receive
   double last_change_date;                // last time I changed a finger or my predecessor
+  RngStream stream;                       //RngStream for
 } s_node_t, *node_t;
 
 /**
@@ -71,13 +75,15 @@ typedef enum {
   TASK_GET_PREDECESSOR_ANSWER,
   TASK_NOTIFY,
   TASK_SUCCESSOR_LEAVING,
-  TASK_PREDECESSOR_LEAVING
+  TASK_PREDECESSOR_LEAVING,
+  TASK_PREDECESSOR_ALIVE,
+  TASK_PREDECESSOR_ALIVE_ANSWER
 } e_task_type_t;
 
-/**
+/*
  * Data attached with the tasks sent and received
  */
-typedef struct task_data {
+typedef struct s_task_data {
   e_task_type_t type;                     // type of task
   int request_id;                         // id paramater (used by some types of tasks)
   int request_finger;                     // finger parameter (used by some types of tasks)
@@ -87,6 +93,7 @@ typedef struct task_data {
 } s_task_data_t, *task_data_t;
 
 static int *powers2;
+static xbt_dynar_t host_list;
 
 // utility functions
 static void chord_initialize(void);
@@ -101,7 +108,7 @@ static void set_predecessor(node_t node, int predecessor_id);
 
 // process functions
 static int node(int argc, char *argv[]);
-static void handle_task(node_t node, m_task_t task);
+static void handle_task(node_t node, msg_task_t task);
 
 // Chord core
 static void create(node_t node);
@@ -117,7 +124,7 @@ static void remote_notify(node_t node, int notify_to, int predecessor_candidate_
 static void fix_fingers(node_t node);
 static void check_predecessor(node_t node);
 static void random_lookup(node_t);
-static void quit_notify(node_t node, int to);
+static void quit_notify(node_t node);
 
 /**
  * \brief Global initialization of the Chord simulation.
@@ -127,17 +134,35 @@ static void chord_initialize(void)
   // compute the powers of 2 once for all
   powers2 = xbt_new(int, nb_bits);
   int pow = 1;
-  int i;
+  unsigned i;
   for (i = 0; i < nb_bits; i++) {
     powers2[i] = pow;
     pow = pow << 1;
   }
   nb_keys = pow;
   XBT_DEBUG("Sets nb_keys to %d", nb_keys);
+
+  msg_host_t host;
+  host_list = MSG_hosts_as_dynar();
+  xbt_dynar_foreach(host_list, i, host) {
+    char descr[512];
+    RngStream stream;
+    snprintf(descr, sizeof descr, "RngSream<%s>", MSG_host_get_name(host));
+    stream = RngStream_CreateStream(descr);
+    MSG_host_set_property_value(host, "stream", (char*)stream, NULL);
+  }
 }
 
 static void chord_exit(void)
 {
+  msg_host_t host;
+  unsigned i;
+  xbt_dynar_foreach(host_list, i, host) {
+    RngStream stream = (RngStream)MSG_host_get_property_value(host, "stream");
+    RngStream_DeleteStream(&stream);
+  }
+  xbt_dynar_free(&host_list);
+
   xbt_free(powers2);
 }
 
@@ -204,8 +229,10 @@ static void get_mailbox(int node_id, char* mailbox)
 static void task_free(void* task)
 {
   // TODO add a parameter data_free_function to MSG_task_create?
-  xbt_free(MSG_task_get_data(task));
-  MSG_task_destroy(task);
+  if(task != NULL){
+    xbt_free(MSG_task_get_data(task));
+    MSG_task_destroy(task);
+  }
 }
 
 /**
@@ -217,9 +244,9 @@ static void print_finger_table(node_t node)
   if (XBT_LOG_ISENABLED(msg_chord, xbt_log_priority_verbose)) {
     int i;
     XBT_VERB("My finger table:");
-    XBT_VERB("Start | Succ ");
+    XBT_VERB("Start | Succ");
     for (i = 0; i < nb_bits; i++) {
-      XBT_VERB(" %3d  | %3d ", (node->id + powers2[i]) % nb_keys, node->fingers[i].id);
+      XBT_VERB(" %3d  | %3d", (node->id + powers2[i]) % nb_keys, node->fingers[i].id);
     }
     XBT_VERB("Predecessor: %d", node->pred_id);
   }
@@ -269,15 +296,16 @@ static void set_predecessor(node_t node, int predecessor_id)
  */
 int node(int argc, char *argv[])
 {
+
   /* Reduce the run size for the MC */
-  if(MC_IS_ENABLED){
+  if(MC_is_active() || MC_record_replay_is_active()){
     periodic_stabilize_delay = 8;
     periodic_fix_fingers_delay = 8;
     periodic_check_predecessor_delay = 8;
   }
 
   double init_time = MSG_get_clock();
-  m_task_t task_received = NULL;
+  msg_task_t task_received = NULL;
   int i;
   int join_success = 0;
   double deadline;
@@ -286,11 +314,16 @@ int node(int argc, char *argv[])
   double next_check_predecessor_date = init_time + periodic_check_predecessor_delay;
   double next_lookup_date = init_time + periodic_lookup_delay;
 
+  int listen = 0;
+  int no_op = 0;
+  int sub_protocol = 0;
+
   xbt_assert(argc == 3 || argc == 5, "Wrong number of arguments for this node");
 
   // initialize my node
   s_node_t node = {0};
-  node.id = atoi(argv[1]);
+  node.id = xbt_str_parse_int(argv[1],"Invalid ID: %s");
+  node.stream = (RngStream)MSG_host_get_property_value(MSG_host_self(), "stream");
   get_mailbox(node.id, node.mailbox);
   node.next_finger_to_fix = 0;
   node.fingers = xbt_new0(s_finger_t, nb_bits);
@@ -302,14 +335,14 @@ int node(int argc, char *argv[])
   }
 
   if (argc == 3) { // first ring
-    deadline = atof(argv[2]);
+    deadline = xbt_str_parse_double(argv[2],"Invalid deadline: %s");
     create(&node);
     join_success = 1;
-  }
-  else {
-    int known_id = atoi(argv[2]);
+
+  } else {
+    int known_id = xbt_str_parse_int(argv[2],"Invalid root ID: %s");
     //double sleep_time = atof(argv[3]);
-    deadline = atof(argv[4]);
+    deadline = xbt_str_parse_double(argv[4],"Invalid deadline: %s");
 
     /*
     // sleep before starting
@@ -323,8 +356,8 @@ int node(int argc, char *argv[])
 
   if (join_success) {
     while (MSG_get_clock() < init_time + deadline
-//	&& MSG_get_clock() < node.last_change_date + 1000
-	&& MSG_get_clock() < max_simulation_time) {
+//      && MSG_get_clock() < node.last_change_date + 1000
+        && MSG_get_clock() < max_simulation_time) {
 
       if (node.comm_receive == NULL) {
         task_received = NULL;
@@ -332,36 +365,54 @@ int node(int argc, char *argv[])
         // FIXME: do not make MSG_task_irecv() calls from several functions
       }
 
+      //XBT_INFO("Node %d is ring member : %d", node.id, is_ring_member(known_id, node.id) != -1);
+
       if (!MSG_comm_test(node.comm_receive)) {
 
         // no task was received: make some periodic calls
-        if (MSG_get_clock() >= next_stabilize_date) {
-          stabilize(&node);
-          next_stabilize_date = MSG_get_clock() + periodic_stabilize_delay;
-        }
-        else if (MSG_get_clock() >= next_fix_fingers_date) {
-          fix_fingers(&node);
-          next_fix_fingers_date = MSG_get_clock() + periodic_fix_fingers_delay;
-        }
-        else if (MSG_get_clock() >= next_check_predecessor_date) {
-          check_predecessor(&node);
-          next_check_predecessor_date = MSG_get_clock() + periodic_check_predecessor_delay;
-        }
-	else if (MSG_get_clock() >= next_lookup_date) {
-	  random_lookup(&node);
-	  next_lookup_date = MSG_get_clock() + periodic_lookup_delay;
-	}
-        else {
-          // nothing to do: sleep for a while
-          MSG_process_sleep(5);
-        }
-      }
 
-      if (node.comm_receive && MSG_comm_test(node.comm_receive)) {
+        if(MC_is_active() || MC_record_replay_is_active()){
+          if(MC_is_active() && !MC_visited_reduction() && no_op){
+              MC_cut();
+          }
+          if(listen == 0 && (sub_protocol = MC_random(0, 4)) > 0){
+            if(sub_protocol == 1)
+              stabilize(&node);
+            else if(sub_protocol == 2)
+              fix_fingers(&node);
+            else if(sub_protocol == 3)
+              check_predecessor(&node);
+            else
+              random_lookup(&node);
+            listen = 1;
+          }else{
+            MSG_process_sleep(sleep_delay);
+            if(!MC_visited_reduction())
+              no_op = 1;
+          }
+        }else{
+          if (MSG_get_clock() >= next_stabilize_date) {
+            stabilize(&node);
+            next_stabilize_date = MSG_get_clock() + periodic_stabilize_delay;
+          }else if (MSG_get_clock() >= next_fix_fingers_date) {
+            fix_fingers(&node);
+            next_fix_fingers_date = MSG_get_clock() + periodic_fix_fingers_delay;
+          }else if (MSG_get_clock() >= next_check_predecessor_date) {
+            check_predecessor(&node);
+            next_check_predecessor_date = MSG_get_clock() + periodic_check_predecessor_delay;
+          }else if (MSG_get_clock() >= next_lookup_date) {
+            random_lookup(&node);
+            next_lookup_date = MSG_get_clock() + periodic_lookup_delay;
+          }else {
+            // nothing to do: sleep for a while
+            MSG_process_sleep(sleep_delay);
+          }
+        }
 
-        // a transfer has occured
+      } else {
+        // a transfer has occurred
 
-        MSG_error_t status = MSG_comm_get_status(node.comm_receive);
+        msg_error_t status = MSG_comm_get_status(node.comm_receive);
 
         if (status != MSG_OK) {
           XBT_DEBUG("Failed to receive a task. Nevermind.");
@@ -378,6 +429,9 @@ int node(int argc, char *argv[])
     }
 
     if (node.comm_receive) {
+      /* handle last task if any */
+      if (MSG_comm_wait(node.comm_receive, 0) == MSG_OK)
+        task_free(task_received);
       MSG_comm_destroy(node.comm_receive);
       node.comm_receive = NULL;
     }
@@ -397,7 +451,7 @@ int node(int argc, char *argv[])
  * \param task the task to handle (don't touch it then:
  * it will be destroyed, reused or forwarded)
  */
-static void handle_task(node_t node, m_task_t task) {
+static void handle_task(node_t node, msg_task_t task) {
 
   XBT_DEBUG("Handling task %p", task);
   char mailbox[MAILBOX_NAME_SIZE];
@@ -406,74 +460,87 @@ static void handle_task(node_t node, m_task_t task) {
 
   switch (type) {
 
-    case TASK_FIND_SUCCESSOR:
-      XBT_DEBUG("Receiving a 'Find Successor' request from %s for id %d",
-          task_data->issuer_host_name, task_data->request_id);
-      // is my successor the successor?
-      if (is_in_interval(task_data->request_id, node->id + 1, node->fingers[0].id)) {
-        task_data->type = TASK_FIND_SUCCESSOR_ANSWER;
-        task_data->answer_id = node->fingers[0].id;
-        XBT_DEBUG("Sending back a 'Find Successor Answer' to %s (mailbox %s): the successor of %d is %d",
-            task_data->issuer_host_name,
-	    task_data->answer_to,
-            task_data->request_id, task_data->answer_id);
-        MSG_task_dsend(task, task_data->answer_to, task_free);
-      }
-      else {
-        // otherwise, forward the request to the closest preceding finger in my table
-        int closest = closest_preceding_node(node, task_data->request_id);
-        XBT_DEBUG("Forwarding the 'Find Successor' request for id %d to my closest preceding finger %d",
-            task_data->request_id, closest);
-        get_mailbox(closest, mailbox);
-        MSG_task_dsend(task, mailbox, task_free);
-      }
-      break;
-
-    case TASK_GET_PREDECESSOR:
-      XBT_DEBUG("Receiving a 'Get Predecessor' request from %s", task_data->issuer_host_name);
-      task_data->type = TASK_GET_PREDECESSOR_ANSWER;
-      task_data->answer_id = node->pred_id;
-      XBT_DEBUG("Sending back a 'Get Predecessor Answer' to %s via mailbox '%s': my predecessor is %d",
-          task_data->issuer_host_name,
-          task_data->answer_to, task_data->answer_id);
+  case TASK_FIND_SUCCESSOR:
+    XBT_DEBUG("Receiving a 'Find Successor' request from %s for id %d",
+              task_data->issuer_host_name, task_data->request_id);
+    // is my successor the successor?
+    if (is_in_interval(task_data->request_id, node->id + 1, node->fingers[0].id)) {
+      task_data->type = TASK_FIND_SUCCESSOR_ANSWER;
+      task_data->answer_id = node->fingers[0].id;
+      XBT_DEBUG("Sending back a 'Find Successor Answer' to %s (mailbox %s): the successor of %d is %d",
+                task_data->issuer_host_name,
+                task_data->answer_to,
+                task_data->request_id, task_data->answer_id);
       MSG_task_dsend(task, task_data->answer_to, task_free);
-      break;
-
-    case TASK_NOTIFY:
-      // someone is telling me that he may be my new predecessor
-      XBT_DEBUG("Receiving a 'Notify' request from %s", task_data->issuer_host_name);
-      notify(node, task_data->request_id);
-      task_free(task);
-      break;
-
-    case TASK_PREDECESSOR_LEAVING:
-      // my predecessor is about to quit
-      XBT_DEBUG("Receiving a 'Predecessor Leaving' message from %s", task_data->issuer_host_name);
-      // modify my predecessor
-      set_predecessor(node, task_data->request_id);
-      task_free(task);
-      /*TODO :
+    }
+    else {
+      // otherwise, forward the request to the closest preceding finger in my table
+      int closest = closest_preceding_node(node, task_data->request_id);
+      XBT_DEBUG("Forwarding the 'Find Successor' request for id %d to my closest preceding finger %d",
+                task_data->request_id, closest);
+      get_mailbox(closest, mailbox);
+      MSG_task_dsend(task, mailbox, task_free);
+    }
+    break;
+
+  case TASK_GET_PREDECESSOR:
+    XBT_DEBUG("Receiving a 'Get Predecessor' request from %s", task_data->issuer_host_name);
+    task_data->type = TASK_GET_PREDECESSOR_ANSWER;
+    task_data->answer_id = node->pred_id;
+    XBT_DEBUG("Sending back a 'Get Predecessor Answer' to %s via mailbox '%s': my predecessor is %d",
+              task_data->issuer_host_name,
+              task_data->answer_to, task_data->answer_id);
+    MSG_task_dsend(task, task_data->answer_to, task_free);
+    break;
+
+  case TASK_NOTIFY:
+    // someone is telling me that he may be my new predecessor
+    XBT_DEBUG("Receiving a 'Notify' request from %s", task_data->issuer_host_name);
+    notify(node, task_data->request_id);
+    task_free(task);
+    break;
+
+  case TASK_PREDECESSOR_LEAVING:
+    // my predecessor is about to quit
+    XBT_DEBUG("Receiving a 'Predecessor Leaving' message from %s", task_data->issuer_host_name);
+    // modify my predecessor
+    set_predecessor(node, task_data->request_id);
+    task_free(task);
+    /*TODO :
       >> notify my new predecessor
       >> send a notify_predecessors !!
-       */
-      break;
-
-    case TASK_SUCCESSOR_LEAVING:
-      // my successor is about to quit
-      XBT_DEBUG("Receiving a 'Successor Leaving' message from %s", task_data->issuer_host_name);
-      // modify my successor FIXME : this should be implicit ?
-      set_finger(node, 0, task_data->request_id);
-      task_free(task);
-      /* TODO
-      >> notify my new successor
-      >> update my table & predecessors table */
-      break;
-
-    case TASK_FIND_SUCCESSOR_ANSWER:
-    case TASK_GET_PREDECESSOR_ANSWER:
-      XBT_DEBUG("Ignoring unexpected task of type %d (%p)", (int)type, task);
-      task_free(task);
-      break;
+    */
+    break;
+
+  case TASK_SUCCESSOR_LEAVING:
+    // my successor is about to quit
+    XBT_DEBUG("Receiving a 'Successor Leaving' message from %s", task_data->issuer_host_name);
+    // modify my successor FIXME : this should be implicit ?
+    set_finger(node, 0, task_data->request_id);
+    task_free(task);
+    /* TODO
+       >> notify my new successor
+       >> update my table & predecessors table */
+    break;
+
+  case TASK_FIND_SUCCESSOR_ANSWER:
+  case TASK_GET_PREDECESSOR_ANSWER:
+  case TASK_PREDECESSOR_ALIVE_ANSWER:
+    XBT_DEBUG("Ignoring unexpected task of type %d (%p)", (int)type, task);
+    task_free(task);
+    break;
+
+  case TASK_PREDECESSOR_ALIVE:
+    XBT_DEBUG("Receiving a 'Predecessor Alive' request from %s", task_data->issuer_host_name);
+    task_data->type = TASK_PREDECESSOR_ALIVE_ANSWER;
+    XBT_DEBUG("Sending back a 'Predecessor Alive Answer' to %s (mailbox %s)",
+              task_data->issuer_host_name,
+              task_data->answer_to);
+    MSG_task_dsend(task, task_data->answer_to, task_free);
+    break;
+
+  default:
+    THROW_IMPOSSIBLE;
   }
 }
 
@@ -526,51 +593,51 @@ static int join(node_t node, int known_id)
 static void leave(node_t node)
 {
   XBT_DEBUG("Well Guys! I Think it's time for me to quit ;)");
-  quit_notify(node, 1);  // notify to my successor ( >>> 1 );
-  quit_notify(node, -1); // notify my predecessor  ( >>> -1);
-  // TODO ...
+  quit_notify(node);
 }
 
-/*
- * \brief Notifies the successor or the predecessor of the current node
+/**
+ * \brief Notifies the successor and the predecessor of the current node
  * of the departure
  * \param node the current node
- * \param to 1 to notify the successor, -1 to notify the predecessor
- * FIXME: notify both nodes with only one call
  */
-static void quit_notify(node_t node, int to)
+static void quit_notify(node_t node)
 {
-  /* TODO
-  task_data_t req_data = xbt_new0(s_task_data_t, 1);
-  req_data->request_id = node->id;
-  req_data->successor_id = node->fingers[0].id;
-  req_data->pred_id = node->pred_id;
+  char mailbox[MAILBOX_NAME_SIZE];
+  //send the PREDECESSOR_LEAVING to our successor
+  task_data_t req_data = xbt_new0(s_task_data_t,1);
+  req_data->type = TASK_PREDECESSOR_LEAVING;
+  req_data->request_id = node->pred_id;
+  get_mailbox(node->id, req_data->answer_to);
   req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
-  req_data->answer_to = NULL;
-  const char* task_name = NULL;
-  const char* to_mailbox = NULL;
-  if (to == 1) {    // notify my successor
-    to_mailbox = node->fingers[0].mailbox;
-    XBT_INFO("Telling my Successor %d about my departure via mailbox %s",
-	  node->fingers[0].id, to_mailbox);
-    req_data->type = TASK_PREDECESSOR_LEAVING;
-  }
-  else if (to == -1) {    // notify my predecessor
-
-    if (node->pred_id == -1) {
-      return;
-    }
 
-    to_mailbox = node->pred_mailbox;
-    XBT_INFO("Telling my Predecessor %d about my departure via mailbox %s",
-	  node->pred_id, to_mailbox);
-    req_data->type = TASK_SUCCESSOR_LEAVING;
+  msg_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+  XBT_DEBUG("Sending a 'PREDECESSOR_LEAVING' to my successor %d",node->fingers[0].id);
+  if (MSG_task_send_with_timeout(task_sent, node->fingers[0].mailbox, timeout)==
+      MSG_TIMEOUT) {
+    XBT_DEBUG("Timeout expired when sending a 'PREDECESSOR_LEAVING' to my successor %d",
+        node->fingers[0].id);
+    task_free(task_sent);
+  }
+
+  //send the SUCCESSOR_LEAVING to our predecessor
+  get_mailbox(node->pred_id, mailbox);
+  task_data_t req_data_s = xbt_new0(s_task_data_t,1);
+  req_data_s->type = TASK_SUCCESSOR_LEAVING;
+  req_data_s->request_id = node->fingers[0].id;
+  req_data_s->request_id = node->pred_id;
+  get_mailbox(node->id, req_data_s->answer_to);
+  req_data_s->issuer_host_name = MSG_host_get_name(MSG_host_self());
+
+  msg_task_t task_sent_s = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data_s);
+  XBT_DEBUG("Sending a 'SUCCESSOR_LEAVING' to my predecessor %d",node->pred_id);
+  if (MSG_task_send_with_timeout(task_sent_s, mailbox, timeout)==
+      MSG_TIMEOUT) {
+    XBT_DEBUG("Timeout expired when sending a 'SUCCESSOR_LEAVING' to my predecessor %d",
+        node->pred_id);
+    task_free(task_sent_s);
   }
-  m_task_t task = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
-  //char* mailbox = get_mailbox(to_mailbox);
-  msg_comm_t comm = MSG_task_isend(task, to_mailbox);
-  xbt_dynar_push(node->comms, &comm);
-  */
+
 }
 
 /**
@@ -611,9 +678,9 @@ static int remote_find_successor(node_t node, int ask_to, int id)
   req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
 
   // send a "Find Successor" request to ask_to_id
-  m_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+  msg_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
   XBT_DEBUG("Sending a 'Find Successor' request (task %p) to %d for id %d", task_sent, ask_to, id);
-  MSG_error_t res = MSG_task_send_with_timeout(task_sent, mailbox, timeout);
+  msg_error_t res = MSG_task_send_with_timeout(task_sent, mailbox, timeout);
 
   if (res != MSG_OK) {
     XBT_DEBUG("Failed to send the 'Find Successor' request (task %p) to %d for id %d",
@@ -628,7 +695,7 @@ static int remote_find_successor(node_t node, int ask_to, int id)
 
     do {
       if (node->comm_receive == NULL) {
-        m_task_t task_received = NULL;
+        msg_task_t task_received = NULL;
         node->comm_receive = MSG_task_irecv(&task_received, node->mailbox);
       }
 
@@ -638,22 +705,33 @@ static int remote_find_successor(node_t node, int ask_to, int id)
         XBT_DEBUG("Failed to receive the answer to my 'Find Successor' request (task %p): %d",
                   task_sent, (int)res);
         stop = 1;
-	MSG_comm_destroy(node->comm_receive);
-	node->comm_receive = NULL;
+        MSG_comm_destroy(node->comm_receive);
+        node->comm_receive = NULL;
       }
       else {
-        m_task_t task_received = MSG_comm_get_task(node->comm_receive);
+        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);
 
-	if (MC_IS_ENABLED) {
-	  MC_assert(task_received == task_sent);
-	}
-
-        if (task_received != task_sent) {
+  // 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 ||
+            ans_data->type != TASK_FIND_SUCCESSOR_ANSWER) {
           // this is not the expected answer
-	  MSG_comm_destroy(node->comm_receive);
-	  node->comm_receive = NULL;
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
           handle_task(node, task_received);
         }
         else {
@@ -662,8 +740,8 @@ static int remote_find_successor(node_t node, int ask_to, int id)
               ans_data->request_id, task_received, id, ans_data->answer_id);
           successor = ans_data->answer_id;
           stop = 1;
-	  MSG_comm_destroy(node->comm_receive);
-	  node->comm_receive = NULL;
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
           task_free(task_received);
         }
       }
@@ -693,8 +771,8 @@ static int remote_get_predecessor(node_t node, int ask_to)
 
   // send a "Get Predecessor" request to ask_to_id
   XBT_DEBUG("Sending a 'Get Predecessor' request to %d", ask_to);
-  m_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
-  MSG_error_t res = MSG_task_send_with_timeout(task_sent, mailbox, timeout);
+  msg_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+  msg_error_t res = MSG_task_send_with_timeout(task_sent, mailbox, timeout);
 
   if (res != MSG_OK) {
     XBT_DEBUG("Failed to send the 'Get Predecessor' request (task %p) to %d",
@@ -709,7 +787,7 @@ static int remote_get_predecessor(node_t node, int ask_to)
 
     do {
       if (node->comm_receive == NULL) { // FIXME simplify this
-        m_task_t task_received = NULL;
+        msg_task_t task_received = NULL;
         node->comm_receive = MSG_task_irecv(&task_received, node->mailbox);
       }
 
@@ -717,22 +795,23 @@ static int remote_get_predecessor(node_t node, int ask_to)
 
       if (res != MSG_OK) {
         XBT_DEBUG("Failed to receive the answer to my 'Get Predecessor' request (task %p): %d",
-                  task_sent, (int)res);
+            task_sent, (int)res);
         stop = 1;
-	MSG_comm_destroy(node->comm_receive);
-	node->comm_receive = NULL;
+        MSG_comm_destroy(node->comm_receive);
+        node->comm_receive = NULL;
       }
       else {
-        m_task_t task_received = MSG_comm_get_task(node->comm_receive);
+        msg_task_t task_received = MSG_comm_get_task(node->comm_receive);
         task_data_t ans_data = MSG_task_get_data(task_received);
 
-	if (MC_IS_ENABLED) {
-	  MC_assert(task_received == task_sent);
-	}
+        /*if (MC_is_active()) {
+          MC_assert(task_received == task_sent);
+          }*/
 
-        if (task_received != task_sent) {
-	  MSG_comm_destroy(node->comm_receive);
-	  node->comm_receive = NULL;
+        if (task_received != task_sent ||
+            ans_data->type != TASK_GET_PREDECESSOR_ANSWER) {
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
           handle_task(node, task_received);
         }
         else {
@@ -740,8 +819,8 @@ static int remote_get_predecessor(node_t node, int ask_to)
               task_received, ask_to, ans_data->answer_id);
           predecessor_id = ans_data->answer_id;
           stop = 1;
-	  MSG_comm_destroy(node->comm_receive);
-	  node->comm_receive = NULL;
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
           task_free(task_received);
         }
       }
@@ -824,18 +903,18 @@ static void notify(node_t node, int predecessor_candidate_id) {
  */
 static void remote_notify(node_t node, int notify_id, int predecessor_candidate_id) {
 
-  task_data_t req_data = xbt_new0(s_task_data_t, 1);
-  req_data->type = TASK_NOTIFY;
-  req_data->request_id = predecessor_candidate_id;
-  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
-
-  // send a "Notify" request to notify_id
-  m_task_t task = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
-  XBT_DEBUG("Sending a 'Notify' request (task %p) to %d", task, notify_id);
-  char mailbox[MAILBOX_NAME_SIZE];
-  get_mailbox(notify_id, mailbox);
-  MSG_task_dsend(task, mailbox, task_free);
-}
+      task_data_t req_data = xbt_new0(s_task_data_t, 1);
+      req_data->type = TASK_NOTIFY;
+      req_data->request_id = predecessor_candidate_id;
+      req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
+
+      // send a "Notify" request to notify_id
+      msg_task_t task = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+      XBT_DEBUG("Sending a 'Notify' request (task %p) to %d", task, notify_id);
+      char mailbox[MAILBOX_NAME_SIZE];
+      get_mailbox(notify_id, mailbox);
+      MSG_task_dsend(task, mailbox, task_free);
+    }
 
 /**
  * \brief This function is called periodically.
@@ -865,7 +944,65 @@ static void fix_fingers(node_t node) {
 static void check_predecessor(node_t node)
 {
   XBT_DEBUG("Checking whether my predecessor is alive");
-  // TODO
+
+  if(node->pred_id == -1)
+    return;
+
+  int stop = 0;
+
+  char mailbox[MAILBOX_NAME_SIZE];
+  get_mailbox(node->pred_id, mailbox);
+  task_data_t req_data = xbt_new0(s_task_data_t,1);
+  req_data->type = TASK_PREDECESSOR_ALIVE;
+  req_data->request_id = node->pred_id;
+  get_mailbox(node->id, req_data->answer_to);
+  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
+
+  msg_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+  XBT_DEBUG("Sending a 'Predecessor Alive' request to my predecessor %d", node->pred_id);
+
+  msg_error_t res = MSG_task_send_with_timeout(task_sent, mailbox, timeout);
+
+  if (res != MSG_OK) {
+    XBT_DEBUG("Failed to send the 'Predecessor Alive' request (task %p) to %d", task_sent, node->pred_id);
+    task_free(task_sent);
+  }else{
+
+    // receive the answer
+    XBT_DEBUG("Sent 'Predecessor Alive' request (task %p) to %d, waiting for the answer on my mailbox '%s'",
+              task_sent, node->pred_id, req_data->answer_to);
+
+    do {
+      if (node->comm_receive == NULL) { // FIXME simplify this
+        msg_task_t task_received = NULL;
+        node->comm_receive = MSG_task_irecv(&task_received, node->mailbox);
+      }
+
+      res = MSG_comm_wait(node->comm_receive, timeout);
+
+      if (res != MSG_OK) {
+        XBT_DEBUG("Failed to receive the answer to my 'Predecessor Alive' request (task %p): %d",
+                  task_sent, (int)res);
+        stop = 1;
+        MSG_comm_destroy(node->comm_receive);
+        node->comm_receive = NULL;
+        node->pred_id = -1;
+      }else {
+        msg_task_t task_received = MSG_comm_get_task(node->comm_receive);
+        if (task_received != task_sent) {
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
+          handle_task(node, task_received);
+        }else{
+          XBT_DEBUG("Received the answer to my 'Predecessor Alive' request (task %p) : my predecessor %d is alive", task_received, node->pred_id);
+          stop = 1;
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
+          task_free(task_received);
+        }
+      }
+    } while (!stop);
+  }
 }
 
 /**
@@ -874,9 +1011,12 @@ static void check_predecessor(node_t node)
  */
 static void random_lookup(node_t node)
 {
-  int id = 1337; // TODO pick a pseudorandom id
-  XBT_DEBUG("Making a lookup request for id %d", id);
-  find_successor(node, id);
+  int random_index = RngStream_RandInt (node->stream, 0, nb_bits - 1);
+  int random_id = node->fingers[random_index].id;
+  XBT_DEBUG("Making a lookup request for id %d", random_id);
+  int res = find_successor(node, random_id);
+  XBT_DEBUG("The successor of node %d is %d", random_id, res);
+
 }
 
 /**
@@ -884,30 +1024,29 @@ static void random_lookup(node_t node)
  */
 int main(int argc, char *argv[])
 {
-  MSG_global_init(&argc, argv);
-  if (argc < 3) {
-    printf("Usage: %s [-nb_bits=n] [-timeout=t] platform_file deployment_file\n", argv[0]);
-    printf("example: %s ../msg_platform.xml chord.xml\n", argv[0]);
-    exit(1);
-  }
+  MSG_init(&argc, argv);
+  xbt_assert(argc > 2, 
+       "Usage: %s [-nb_bits=n] [-timeout=t] platform_file deployment_file\n"
+       "\tExample: %s ../msg_platform.xml chord.xml\n", 
+       argv[0], argv[0]);
 
   char **options = &argv[1];
   while (!strncmp(options[0], "-", 1)) {
 
     int length = strlen("-nb_bits=");
     if (!strncmp(options[0], "-nb_bits=", length) && strlen(options[0]) > length) {
-      nb_bits = atoi(options[0] + length);
+      nb_bits = xbt_str_parse_int(options[0] + length, "Invalid nb_bits parameter: %s");
       XBT_DEBUG("Set nb_bits to %d", nb_bits);
     }
     else {
 
       length = strlen("-timeout=");
       if (!strncmp(options[0], "-timeout=", length) && strlen(options[0]) > length) {
-	timeout = atoi(options[0] + length);
-	XBT_DEBUG("Set timeout to %d", timeout);
+        timeout = xbt_str_parse_int(options[0] + length, "Invalid timeout parameter: %s");
+        XBT_DEBUG("Set timeout to %d", timeout);
       }
       else {
-	xbt_die("Invalid chord option '%s'", options[0]);
+        xbt_die("Invalid chord option '%s'", options[0]);
       }
     }
     options++;
@@ -916,22 +1055,18 @@ int main(int argc, char *argv[])
   const char* platform_file = options[0];
   const char* application_file = options[1];
 
-  chord_initialize();
-
   MSG_create_environment(platform_file);
 
+  chord_initialize();
+
   MSG_function_register("node", node);
   MSG_launch_application(application_file);
 
-  MSG_error_t res = MSG_main();
+  msg_error_t res = MSG_main();
   XBT_CRITICAL("Messages created: %ld", smx_total_comms);
   XBT_INFO("Simulated time: %g", MSG_get_clock());
 
-  MSG_clean();
   chord_exit();
 
-  if (res == MSG_OK)
-    return 0;
-  else
-    return 1;
+  return res != MSG_OK;
 }