X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/7b28e9e1bfe2348d1a820e78d8867ba325dcd03b..8feb1c4d2fe696b8f0c723eac3d88024976f6825:/examples/msg/chord/chord.c

diff --git a/examples/msg/chord/chord.c b/examples/msg/chord/chord.c
index 7b9bf0eed9..7289d43b36 100644
--- a/examples/msg/chord/chord.c
+++ b/examples/msg/chord/chord.c
@@ -1,5 +1,5 @@
 
-/* Copyright (c) 2010. The SimGrid Team.
+/* Copyright (c) 2010-2013. The SimGrid Team.
  * All rights reserved.                                                     */
 
 /* This program is free software; you can redistribute it and/or modify it
@@ -9,64 +9,107 @@
 #include "msg/msg.h"
 #include "xbt/log.h"
 #include "xbt/asserts.h"
+#include "simgrid/modelchecker.h"
+#include <xbt/RngStream.h>
+
+/** @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 
+ *    demonstrated in http://hal.inria.fr/inria-00602216/
+ */
+
+ 
 XBT_LOG_NEW_DEFAULT_CATEGORY(msg_chord,
                              "Messages specific for this msg example");
 
-#define NB_BITS 6
-#define NB_KEYS 64
+#define COMM_SIZE 10
+#define COMP_SIZE 0
+#define MAILBOX_NAME_SIZE 10
 
-/**
+static int nb_bits = 24;
+static int nb_keys = 0;
+static int timeout = 50;
+static int max_simulation_time = 1000;
+static int periodic_stabilize_delay = 20;
+static int periodic_fix_fingers_delay = 120;
+static int periodic_check_predecessor_delay = 120;
+static int periodic_lookup_delay = 10;
+
+extern long int smx_total_comms;
+
+/*
  * Finger element.
  */
-typedef struct finger {
+typedef struct s_finger {
   int id;
-  char* mailbox;
+  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;                          // my usual mailbox name
-  s_finger_t fingers[NB_BITS];            // finger table (fingers[0] is my successor)
+  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)
   int pred_id;                            // predecessor id
-  char* pred_mailbox;                     // predecessor's mailbox name
+  char pred_mailbox[MAILBOX_NAME_SIZE];   // predecessor's mailbox name
   int next_finger_to_fix;                 // index of the next finger to fix in fix_fingers()
-  xbt_dynar_t comms;                      // current communications pending
+  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;
 
 /**
- * Task data
+ * Types of tasks exchanged between nodes.
  */
-typedef struct task_data {
-  int request_id;
-  int request_finger;
-  int answer_id;
-  const char* answer_to;
-  const char* issuer_host_name; // used for logging
-  int successor_id;				// used when quitting
-  int pred_id;  				// used when quitting
-  // FIXME: remove successor_id and pred_id, request_id is enough
+typedef enum {
+  TASK_FIND_SUCCESSOR,
+  TASK_FIND_SUCCESSOR_ANSWER,
+  TASK_GET_PREDECESSOR,
+  TASK_GET_PREDECESSOR_ANSWER,
+  TASK_NOTIFY,
+  TASK_SUCCESSOR_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 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)
+  int answer_id;                          // answer (used by some types of tasks)
+  char answer_to[MAILBOX_NAME_SIZE];      // mailbox to send an answer to (if any)
+  const char* issuer_host_name;           // used for logging
 } s_task_data_t, *task_data_t;
 
-static int powers2[NB_BITS];
+static int *powers2;
 
 // utility functions
 static void chord_initialize(void);
+static void chord_exit(void);
 static int normalize(int id);
 static int is_in_interval(int id, int start, int end);
-static char* get_mailbox(int host_id);
+static void get_mailbox(int host_id, char* mailbox);
+static void task_free(void* task);
 static void print_finger_table(node_t node);
 static void set_finger(node_t node, int finger_index, int id);
 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, msg_task_t task);
 
 // Chord core
 static void create(node_t node);
-static void join(node_t node, int known_id);
+static int join(node_t node, int known_id);
 static void leave(node_t node);
 static int find_successor(node_t node, int id);
 static int remote_find_successor(node_t node, int ask_to_id, int id);
@@ -77,57 +120,46 @@ static void notify(node_t node, int predecessor_candidate_id);
 static void remote_notify(node_t node, int notify_to, int predecessor_candidate_id);
 static void fix_fingers(node_t node);
 static void check_predecessor(node_t node);
-static void quit_notify(node_t node, int to);
-
-// not implemented yet
-//static void remote_move_keys(node_t node, int take_from_id);
-
-// deprecated
-/*
-static void bootstrap(node_t node, int known_id);
-static int find_predecessor(node_t node, int id);
-static int remote_find_predecessor(node_t node, int ask_to_id, int id);
-static int remote_closest_preceding_finger(int ask_to_id, int id);
-static void notify_predecessors(node_t node);
-static void initialize_finger_table(node_t data, int known_id);
-static void update_finger_table(node_t node, int candidate_id, int finger_index);
-static void remote_update_finger_table(node_t node, int ask_to_id, int candidate_id, int finger_index);
-static void notify_node_joined(node_t node, int new_node_id);
-static void remote_notify_node_joined(node_t node, int notify_id);
-*/
+static void random_lookup(node_t);
+static void quit_notify(node_t node);
 
+/**
+ * \brief Global initialization of the Chord simulation.
+ */
 static void chord_initialize(void)
 {
   // compute the powers of 2 once for all
+  powers2 = xbt_new(int, nb_bits);
   int pow = 1;
   int i;
-  for (i = 0; i < NB_BITS; 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);
+}
+
+static void chord_exit(void)
+{
+  xbt_free(powers2);
 }
 
 /**
- * \brief Turns an id into an equivalent id in [0, NB_KEYS[
+ * \brief Turns an id into an equivalent id in [0, nb_keys).
  * \param id an id
  * \return the corresponding normalized id
  */
 static int normalize(int id)
 {
-  // make sure id >= 0
-  while (id < 0) {
-    id += NB_KEYS;
-  }
-  // make sure id < NB_KEYS
-  id = id % NB_KEYS;
-
-  return id;
+  // like id % nb_keys, but works with negatives numbers (and faster)
+  return id & (nb_keys - 1);
 }
 
 /**
- * \brief Returns whether a id belongs to the interval [start, end].
+ * \brief Returns whether an id belongs to the interval [start, end].
  *
- * The parameters are noramlized to make sure they are between 0 and CHORD_NB_KEYS - 1).
+ * The parameters are noramlized to make sure they are between 0 and nb_keys - 1).
  * 1 belongs to [62, 3]
  * 1 does not belong to [3, 62]
  * 63 belongs to [62, 3]
@@ -148,11 +180,11 @@ static int is_in_interval(int id, int start, int end)
 
   // make sure end >= start and id >= start
   if (end < start) {
-    end += NB_KEYS;
+    end += nb_keys;
   }
 
   if (id < start) {
-    id += NB_KEYS;
+    id += nb_keys;
   }
 
   return id <= end;
@@ -161,12 +193,25 @@ static int is_in_interval(int id, int start, int end)
 /**
  * \brief Gets the mailbox name of a host given its chord id.
  * \param node_id id of a node
- * \return the name of its mailbox
- * FIXME: free the memory
+ * \param mailbox pointer to where the mailbox name should be written
+ * (there must be enough space)
  */
-static char* get_mailbox(int node_id)
+static void get_mailbox(int node_id, char* mailbox)
 {
-  return bprintf("mailbox%d", node_id);
+  snprintf(mailbox, MAILBOX_NAME_SIZE - 1, "%d", node_id);
+}
+
+/**
+ * \brief Frees the memory used by a task.
+ * \param task the MSG task to destroy
+ */
+static void task_free(void* task)
+{
+  // TODO add a parameter data_free_function to MSG_task_create?
+  if(task != NULL){
+    xbt_free(MSG_task_get_data(task));
+    MSG_task_destroy(task);
+  }
 }
 
 /**
@@ -175,29 +220,31 @@ static char* get_mailbox(int node_id)
  */
 static void print_finger_table(node_t node)
 {
-  int i;
-  int pow = 1;
-  INFO0("My finger table:");
-  INFO0("Start | Succ ");
-  for (i = 0; i < NB_BITS; i++) {
-    INFO2(" %3d  | %3d ", (node->id + pow) % NB_KEYS, node->fingers[i].id);
-    pow = pow << 1;
+  if (XBT_LOG_ISENABLED(msg_chord, xbt_log_priority_verbose)) {
+    int i;
+    XBT_VERB("My finger table:");
+    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("Predecessor: %d", node->pred_id);
   }
-  INFO1("Predecessor: %d", node->pred_id);
 }
 
 /**
  * \brief Sets a finger of the current node.
  * \param node the current node
- * \param finger_index index of the finger to set (0 to NB_BITS - 1)
+ * \param finger_index index of the finger to set (0 to nb_bits - 1)
  * \param id the id to set for this finger
  */
 static void set_finger(node_t node, int finger_index, int id)
 {
-  node->fingers[finger_index].id = id;
-  xbt_free(node->fingers[finger_index].mailbox);
-  node->fingers[finger_index].mailbox = get_mailbox(id);
-  INFO2("My new finger #%d is %d", finger_index, id);
+  if (id != node->fingers[finger_index].id) {
+    node->fingers[finger_index].id = id;
+    get_mailbox(id, node->fingers[finger_index].mailbox);
+    node->last_change_date = MSG_get_clock();
+    XBT_DEBUG("My new finger #%d is %d", finger_index, id);
+  }
 }
 
 /**
@@ -207,14 +254,16 @@ static void set_finger(node_t node, int finger_index, int id)
  */
 static void set_predecessor(node_t node, int predecessor_id)
 {
-  node->pred_id = predecessor_id;
-  xbt_free(node->pred_mailbox);
+  if (predecessor_id != node->pred_id) {
+    node->pred_id = predecessor_id;
 
-  if (predecessor_id != -1) {
-    node->pred_mailbox = get_mailbox(predecessor_id);
-  }
+    if (predecessor_id != -1) {
+      get_mailbox(predecessor_id, node->pred_mailbox);
+    }
+    node->last_change_date = MSG_get_clock();
 
-  INFO1("My new predecessor is %d", predecessor_id);
+    XBT_DEBUG("My new predecessor is %d", predecessor_id);
+  }
 }
 
 /**
@@ -226,194 +275,267 @@ 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_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 = NULL;
-  msg_comm_t comm_send = NULL;
-  msg_comm_t comm_receive = NULL;
+  msg_task_t task_received = NULL;
   int i;
-  char* mailbox = NULL;
+  int join_success = 0;
   double deadline;
-  double next_stabilize_date = init_time + 10;
-  double next_fix_fingers_date = init_time + 10;
-  double next_check_predecessor_date = init_time + 10;
+  double next_stabilize_date = init_time + periodic_stabilize_delay;
+  double next_fix_fingers_date = init_time + periodic_fix_fingers_delay;
+  double next_check_predecessor_date = init_time + periodic_check_predecessor_delay;
+  double next_lookup_date = init_time + periodic_lookup_delay;
+
+  #ifdef HAVE_MC
+  int listen = 0;
+  int no_op = 0;
+  int sub_protocol = 0;
+  #endif
 
-  xbt_assert0(argc == 3 || argc == 5, "Wrong number of arguments for this node");
+  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.mailbox = get_mailbox(node.id);
+  get_mailbox(node.id, node.mailbox);
   node.next_finger_to_fix = 0;
-  node.comms = xbt_dynar_new(sizeof(msg_comm_t), NULL);
+  node.fingers = xbt_new0(s_finger_t, nb_bits);
+  node.last_change_date = init_time;
 
-  for (i = 0; i < NB_BITS; i++) {
+  for (i = 0; i < nb_bits; i++) {
+    node.fingers[i].id = -1;
     set_finger(&node, i, node.id);
   }
 
   if (argc == 3) { // first ring
     deadline = atof(argv[2]);
     create(&node);
+    join_success = 1;
   }
   else {
     int known_id = atoi(argv[2]);
-    double sleep_time = atof(argv[3]);
+    //double sleep_time = atof(argv[3]);
     deadline = atof(argv[4]);
 
+    /*
     // sleep before starting
-    INFO1("Let's sleep during %f", sleep_time);
+    XBT_DEBUG("Let's sleep during %f", sleep_time);
     MSG_process_sleep(sleep_time);
-    INFO0("Hey! Let's join the system.");
+    */
+    XBT_DEBUG("Hey! Let's join the system.");
 
-    join(&node, known_id);
+    join_success = join(&node, known_id);
   }
 
-  while (MSG_get_clock() < init_time + deadline) {
+  if (join_success) {
+    while (MSG_get_clock() < init_time + deadline
+//      && MSG_get_clock() < node.last_change_date + 1000
+        && MSG_get_clock() < max_simulation_time) {
+
+      if (node.comm_receive == NULL) {
+        task_received = NULL;
+        node.comm_receive = MSG_task_irecv(&task_received, node.mailbox);
+        // FIXME: do not make MSG_task_irecv() calls from several functions
+      }
 
-    // see if some communications are finished
-    int index;
-    while ((index = MSG_comm_testany(node.comms)) != -1) {
-      comm_send = xbt_dynar_get_as(node.comms, index, msg_comm_t);
-      xbt_dynar_remove_at(node.comms, index, &comm_send);
-      MSG_comm_destroy(comm_send);
+      //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
+
+#ifdef HAVE_MC
+        if(MC_is_active()){
+          if(!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(5);
+            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(5);
+          }
+        }
+#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(5);
+        }
+#endif
+
+      } else {
+        // a transfer has occurred
+
+        msg_error_t status = MSG_comm_get_status(node.comm_receive);
+
+        if (status != MSG_OK) {
+          XBT_DEBUG("Failed to receive a task. Nevermind.");
+          MSG_comm_destroy(node.comm_receive);
+          node.comm_receive = NULL;
+        }
+        else {
+          // the task was successfully received
+          MSG_comm_destroy(node.comm_receive);
+          node.comm_receive = NULL;
+          handle_task(&node, task_received);
+        }
+      }
     }
 
-    if (comm_receive == NULL) {
-      task = NULL;
-      comm_receive = MSG_task_irecv(&task, node.mailbox);
+    if (node.comm_receive) {
+      MSG_comm_destroy(node.comm_receive);
+      node.comm_receive = NULL;
     }
 
-    if (!MSG_comm_test(comm_receive)) {
+    // leave the ring
+    leave(&node);
+  }
 
-      // no task was received: make some periodic calls
-      if (MSG_get_clock() >= next_stabilize_date) {
-        stabilize(&node);
-        next_stabilize_date = MSG_get_clock() + 10;
-      }
-      else if (MSG_get_clock() >= next_fix_fingers_date) {
-        fix_fingers(&node);
-        next_fix_fingers_date = MSG_get_clock() + 10;
-      }
-      else if (MSG_get_clock() >= next_check_predecessor_date) {
-        check_predecessor(&node);
-        next_check_predecessor_date = MSG_get_clock() + 10;
-      }
-      else {
-	// nothing to do: sleep for a while
-        MSG_process_sleep(5);
-      }
-    }
-    else {
-      // a task was received
+  // stop the simulation
+  xbt_free(node.fingers);
+  return 0;
+}
 
-      MSG_comm_destroy(comm_receive);
-      comm_receive = NULL;
-      const char* task_name = MSG_task_get_name(task);
-      task_data_t task_data = (task_data_t) MSG_task_get_data(task);
+/**
+ * \brief This function is called when the current node receives a task.
+ * \param node the current node
+ * \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, msg_task_t task) {
 
-      if (!strcmp(task_name, "Find Successor")) {
-        INFO2("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->answer_id = node.fingers[0].id;
-	  MSG_task_set_name(task, "Find Successor Answer");
-	  INFO3("Sending back a 'Find Successor Answer' to %s: the successor of %d is %d",
-	        task_data->issuer_host_name, task_data->request_id, task_data->answer_id);
-	  comm_send = MSG_task_isend(task, task_data->answer_to);
-	  xbt_dynar_push(node.comms, &comm_send);
-	}
-	else {
-	  // otherwise, forward the request to the closest preceding finger in my table
-	  int closest = closest_preceding_node(&node, task_data->request_id);
-	  INFO2("Forwarding the 'Find Successor' request for id %d to my closest preceding finger %d",
-	        task_data->request_id, closest);
-	  mailbox = get_mailbox(closest);
-	  comm_send = MSG_task_isend(task, mailbox);
-	  xbt_dynar_push(node.comms, &comm_send);
-	  xbt_free(mailbox);
-	}
-      }
+  XBT_DEBUG("Handling task %p", task);
+  char mailbox[MAILBOX_NAME_SIZE];
+  task_data_t task_data = (task_data_t) MSG_task_get_data(task);
+  e_task_type_t type = task_data->type;
 
-      else if (!strcmp(task_name, "Get Predecessor")) {
-	INFO1("Receiving a 'Get Predecessor' Request from %s", task_data->issuer_host_name);
-	task_data->answer_id = node.pred_id;
-	MSG_task_set_name(task, "Get Predecessor Answer");
-	INFO2("Sending back a 'Get Predecessor Answer' to %s: my predecessor is %d",
-	      task_data->issuer_host_name, task_data->answer_id);
-	comm_send = MSG_task_isend(task, task_data->answer_to);
-	xbt_dynar_push(node.comms, &comm_send);
-      }
-      /*
-      else if (!strcmp(task_name, "Find Predecessor")) {
-	INFO2("Receiving a 'Find Predecessor' Request from %s for id %d", task_data->issuer_host_name, task_data->request_id);
-	// am I the predecessor?
-	if (is_in_interval(task_data->request_id, node.id + 1, node.fingers[0].id)) {
-	  task_data->answer_id = node.id;
-	  MSG_task_set_name(task, "Find Predecessor Answer");
-	  INFO3("Sending back a 'Find Predecessor' Answer to %s: the predecessor of %d is %d", task_data->issuer_host_name, task_data->request_id, task_data->answer_id);
-	  comm = MSG_task_isend(task, task_data->answer_to);
-	  xbt_dynar_push(node.comms, &comm);
-	}
-	else {
-	  // otherwise, forward the request to the closest preceding finger in my table
-	  int closest = closest_preceding_node(&node, task_data->request_id);
-	  INFO2("Forwarding 'Find Predecessor' request for id %d to my closest preceding finger %d", task_data->request_id, closest);
-	  mailbox = get_mailbox(closest);
-	  comm = MSG_task_isend(task, mailbox);
-	  xbt_dynar_push(node.comms, &comm);
-	  xbt_free(mailbox);
-	}
-      }
-      */
+  switch (type) {
 
-      /*
-      else if (!strcmp(task_name, "Notify Node Joined")) {
-	// someone may be my new neighboor
-	INFO1("Receiving a 'Notify Node Joine' request from %s", task_data->issuer_host_name);
-	notify_node_joined(&node, task_data->request_id);
-      }
-      else if (!strcmp(task_name, "Update Finger")) {
-	// someone is telling me that he may be my new finger
-	INFO1("Receiving an 'Update Finger' request from %s", task_data->issuer_host_name);
-	update_finger_table(&node, task_data->request_id, task_data->request_finger);
-      }
-      */
-      else if (!strcmp(task_name, "Notify")) {
-	// someone is telling me that he may be my new predecessor
-	INFO1("Receiving a 'Notify' request from %s", task_data->issuer_host_name);
-	notify(&node, task_data->request_id);
-      }
-      else if (!strcmp(task_name, "Predecessor Leaving")) {
-	// my predecessor is about to quit
-	INFO1("Receiving a 'Predecessor Leaving' message from %s", task_data->issuer_host_name);
-	// modify my predecessor
-	set_predecessor(&node, task_data->pred_id);
-	/*TODO :
-          >> notify my new predecessor
-          >> send a notify_predecessors !!
-	 */
-      }
-      else if (!strcmp(task_name, "Successor Leaving")) {
-	// my successor is about to quit
-	INFO1("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->successor_id);
-	/* TODO
-          >> notify my new successor
-          >> update my table & predecessors table */
-      }
+  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);
+    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:
+  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;
 
-  // leave the ring and stop the simulation
-  leave(&node);
-  xbt_dynar_free(&node.comms);
-  xbt_free(node.mailbox);
-  xbt_free(node.pred_mailbox);
-  for (i = 0; i < NB_BITS - 1; i++) {
-    xbt_free(node.fingers[i].mailbox);
   }
-  return 0;
 }
 
 /**
@@ -422,7 +544,7 @@ int node(int argc, char *argv[])
  */
 static void create(node_t node)
 {
-  INFO0("Create a new Chord ring...");
+  XBT_DEBUG("Create a new Chord ring...");
   set_predecessor(node, -1); // -1 means that I have no predecessor
   print_finger_table(node);
 }
@@ -432,93 +554,31 @@ static void create(node_t node)
  * already in the ring
  * \param node the current node
  * \param known_id id of a node already in the ring
+ * \return 1 if the join operation succeeded, 0 otherwise
  */
-static void join(node_t node, int known_id)
+static int join(node_t node, int known_id)
 {
-  INFO2("Joining the ring with id %d, knowing node %d", node->id, known_id);
+  XBT_INFO("Joining the ring with id %d, knowing node %d", node->id, known_id);
   set_predecessor(node, -1); // no predecessor (yet)
 
-  int successor_id;
-  do {
-    successor_id = remote_find_successor(node, known_id, node->id);
-    INFO0("My 'Find Successor' request has failed, let's try again");
-  } while (successor_id == -1);
-
-  set_finger(node, 0, successor_id);
-  print_finger_table(node);
-}
-
-/**
- * \brief Notifies the current node that a node has just joined the network.
- * \param node the current node
- * \param new_node_id id of the new node in the network
- */
-/*
-static void notify_node_joined(node_t node, int new_node_id)
-{
-  INFO1("A new node %d has joined the network, let's see if it is a neighboor", new_node_id);
-  if (is_in_interval(new_node_id, node->id + 1, node->fingers[0].id - 1)) {
-    // new_node_id is my new successor
-    set_finger(node, 0, new_node_id);
-    bootstrap(node, new_node_id);
+  /*
+  int i;
+  for (i = 0; i < nb_bits; i++) {
+    set_finger(node, i, known_id);
   }
+  */
 
-  if (is_in_interval(new_node_id, node->pred_id + 1, node->id - 1)) {
-    // new_node_id is my new predecessor
-    set_predecessor(node, new_node_id);
-    bootstrap(node, new_node_id);
+  int successor_id = remote_find_successor(node, known_id, node->id);
+  if (successor_id == -1) {
+    XBT_INFO("Cannot join the ring.");
   }
-}
-*/
-
-/**
- * \brief Notifies a remote node that the current node has just joined
- * the network.
- * \param node the current node
- * \param notify_id id of the remote node to notify
- */
-/*
-static void remote_notify_node_joined(node_t node, int notify_id)
-{
-  task_data_t req_data = xbt_new0(s_task_data_t, 1);
-  req_data->request_id = node->id;
-  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
-
-  // send a "Notify" request to notify_id
-  INFO2("Sending a 'Notify' request to %d because I have joined the network with id %d", notify_id, node->id);
-  m_task_t task = MSG_task_create("Notify", 1000, 5000, req_data);
-  char* mailbox = get_mailbox(notify_id);
-  msg_comm_t comm = MSG_task_isend(task, mailbox);
-  xbt_dynar_push(node->comms, &comm);
-  xbt_free(mailbox);
-}
-*/
-
-/**
-* \brief Let the current node send queries to fill in its own finger table.
-* \param node the current node
-* \param ask_to_id id of a node to send queries to
-*/
-/*
-static void bootstrap(node_t node, int ask_to_id)
-{
-  INFO0("Filling my finger table");
-  int i, pred_id, succ_id;
-  int pow = 1;
-
-  for (i = 0; i < NB_BITS; i++)
-  {
-    pred_id = remote_find_successor(node, ask_to_id, pow);
-    do {
-      succ_id = pred_id;
-      pred_id = remote_find_predecessor(node, pred_id, pred_id);
-    } while (pred_id >= pow);
-
-    pow = pow << 1;
-    set_finger(node, i, succ_id);
+  else {
+    set_finger(node, 0, successor_id);
+    print_finger_table(node);
   }
+
+  return successor_id != -1;
 }
-*/
 
 /**
  * \brief Makes the current node quit the system
@@ -526,168 +586,54 @@ static void bootstrap(node_t node, int ask_to_id)
  */
 static void leave(node_t node)
 {
-  INFO0("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 ...
+  XBT_DEBUG("Well Guys! I Think it's time for me to quit ;)");
+  quit_notify(node);
+  RngStream_DeleteStream(&node->stream);
 }
 
-/*
- * \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)
 {
-  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());
-  const char *task_name = NULL;
-  const char* to_mailbox = NULL;
-  if (to == 1)    // notify my successor
-  {
-    to_mailbox = node->fingers[0].mailbox;
-    INFO2("Telling my Successor %d about my departure via mailbox %s",
-	  node->fingers[0].id, to_mailbox);
-    task_name = "Predecessor Leaving";
-
-  }
-  else if (to == -1)    // notify my predecessor
-  {
-    if (node->pred_id == -1) {
-      return;
-    }
-
-    to_mailbox = node->pred_mailbox;
-    INFO2("Telling my Predecessor %d about my departure via mailbox %s",
-	  node->pred_id, to_mailbox);
-    task_name = "Predecessor 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);
   }
-  m_task_t task = MSG_task_create(task_name, 1000, 5000, req_data);
-  //char* mailbox = get_mailbox(to_mailbox);
-  msg_comm_t comm = MSG_task_isend(task, to_mailbox);
-  xbt_dynar_push(node->comms, &comm);
-}
-
-/*
- * \brief Initializes my finger table, knowing the id of a node already in the system.
- * \param node the current node
- * \param known_id id of a node already in the system
- */
-/*
-static void initialize_finger_table(node_t node, int known_id)
-{
-  int my_id = node->id;
-  int i;
-  int pow = 1; // 2^i
-
-  INFO0("Initializing my finger table...");
-
-  // ask known_id who is my immediate successor
-  node->fingers[0].id = remote_find_successor(node, known_id, my_id + 1);
-  node->fingers[0].mailbox = get_mailbox(node->fingers[0].id);
-
-  // find all other fingers
-  for (i = 0; i < NB_BITS - 1; i++) {
 
-    pow = pow << 1; // equivalent to pow = pow * 2
-    if (is_in_interval(my_id + pow, my_id, node->fingers[i].id - 1)) {
-      // I already have the info for this finger
-      node->fingers[i + 1].id = node->fingers[i].id;
-    }
-    else {
-      // I don't have the info, ask the only guy I know
-      node->fingers[i + 1].id = remote_find_successor(node, known_id, my_id + pow);
-    }
-    node->fingers[i + 1].mailbox = get_mailbox(node->fingers[i + 1].id);
-  }
-
-  node->pred_id = find_predecessor(node, node->id);
-  node->pred_mailbox = get_mailbox(node->pred_id);
-
-  INFO0("Finger table initialized!");
-  print_finger_table(node);
-}
-*/
-
-/**
- * \brief Notifies some nodes that the current node may have became their finger.
- * \param node the current node, which has just joined the system
- */
-/*
-static void notify_predecessors(node_t node)
-{
-  int i, pred_id;
-  int pow = 1;
-  for (i = 0; i < NB_BITS; i++) {
-    // find the closest node whose finger #i can be me
-    pred_id = find_predecessor(node, node->id - pow + 1); // note: no "+1" in the article!
-    if (pred_id != node->id) {
-      remote_update_finger_table(node, pred_id, node->id, i);
-    }
-    pow = pow << 1; // pow = pow * 2
+  //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);
   }
-}
-*/
 
-/**
- * \brief Tells the current node that a node may have became its new finger.
- * \param node the current node
- * \param candidate_id id of the node that may be a new finger of the current node
- * \param finger_index index of the finger to update
- */
-/*
-static void update_finger_table(node_t node, int candidate_id, int finger_index)
-{
-  int pow = 1;
-  int i;
-  for (i = 0; i < finger_index; i++) {
-    pow = pow << 1;
-  }
-
-  //  if (is_in_interval(candidate_id, node->id + pow, node->fingers[finger_index].id - 1)) {
-  if (is_in_interval(candidate_id, node->id, node->fingers[finger_index].id - 1)) {
-//    INFO3("Candidate %d is between %d and %d!", candidate_id, node->id + pow, node->fingers[finger_index].id - 1);
-    // candidate_id is my new finger
-    set_finger(node, finger_index, candidate_id);
-    print_finger_table(node);
-
-    if (node->pred_id != node->id) { // FIXME: is this necessary?
-      // my predecessor may be concerned too
-      remote_update_finger_table(node, node->pred_id, candidate_id, finger_index);
-    }
-  }
 }
-*/
-
-/**
- * \brief Tells a remote node that a node may have became its new finger.
- * \param ask_to_id id of the remote node to update
- * \param candidate_id id of the node that may be a new finger of the remote node
- * \param finger_index index of the finger to update
- */
-/*
-static void remote_update_finger_table(node_t node, int ask_to_id, int candidate_id, int finger_index)
-{
-  task_data_t req_data = xbt_new0(s_task_data_t, 1);
-  req_data->request_id = candidate_id;
-  req_data->request_finger = finger_index;
-  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
-
-  // send a "Update Finger" request to ask_to_id
-  INFO3("Sending an 'Update Finger' request to %d: his finger #%d may be %d now", ask_to_id, finger_index, candidate_id);
-  m_task_t task = MSG_task_create("Update Finger", 1000, 5000, req_data);
-  char* mailbox = get_mailbox(ask_to_id);
-  msg_comm_t comm = MSG_task_isend(task, mailbox);
-  xbt_dynar_push(node->comms, &comm);
-  xbt_free(mailbox);
-}
-*/
 
 /**
  * \brief Makes the current node find the successor node of an id.
@@ -717,32 +663,85 @@ static int find_successor(node_t node, int id)
 static int remote_find_successor(node_t node, int ask_to, int id)
 {
   int successor = -1;
-  s_task_data_t req_data;
-  char* mailbox = bprintf("%s Find Successor", node->mailbox);
-  req_data.request_id = id;
-  req_data.answer_to = mailbox;
-  req_data.issuer_host_name = MSG_host_get_name(MSG_host_self());
+  int stop = 0;
+  char mailbox[MAILBOX_NAME_SIZE];
+  get_mailbox(ask_to, mailbox);
+  task_data_t req_data = xbt_new0(s_task_data_t, 1);
+  req_data->type = TASK_FIND_SUCCESSOR;
+  req_data->request_id = id;
+  get_mailbox(node->id, req_data->answer_to);
+  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
 
   // send a "Find Successor" request to ask_to_id
-  INFO2("Sending a 'Find Successor' request to %d for key %d", ask_to, id);
-  m_task_t task = MSG_task_create("Find Successor", 1000, 5000, &req_data);
-  MSG_error_t res = MSG_task_send_with_timeout(task, get_mailbox(ask_to), 20);
-  if (res == MSG_OK) {
+  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);
+
+  if (res != MSG_OK) {
+    XBT_DEBUG("Failed to send the 'Find Successor' request (task %p) to %d for id %d",
+        task_sent, ask_to, id);
+    task_free(task_sent);
+  }
+  else {
 
     // receive the answer
-    task = NULL;
-    res = MSG_task_receive_with_timeout(&task, req_data.answer_to, 20);
+    XBT_DEBUG("Sent a 'Find Successor' request (task %p) to %d for key %d, waiting for the answer",
+        task_sent, ask_to, id);
 
-    if (res == MSG_OK) {
+    do {
+      if (node->comm_receive == NULL) {
+        msg_task_t task_received = NULL;
+        node->comm_receive = MSG_task_irecv(&task_received, node->mailbox);
+      }
 
-      task_data_t ans_data;
-      ans_data = MSG_task_get_data(task);
-      successor = ans_data->answer_id;
-      INFO2("Received the answer to my 'Find Successor' request: the successor of key %d is %d", id, successor);
-    }
+      res = MSG_comm_wait(node->comm_receive, timeout);
+
+      if (res != MSG_OK) {
+        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;
+      }
+      else {
+        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);
+
+	// 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) {
+          // this is not the expected answer
+          MSG_comm_destroy(node->comm_receive);
+          node->comm_receive = NULL;
+          handle_task(node, task_received);
+        }
+        else {
+          // this is our answer
+          XBT_DEBUG("Received the answer to my 'Find Successor' request for id %d (task %p): the successor of key %d is %d",
+              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;
+          task_free(task_received);
+        }
+      }
+    } while (!stop);
   }
 
-  xbt_free(mailbox);
   return successor;
 }
 
@@ -756,90 +755,73 @@ static int remote_find_successor(node_t node, int ask_to, int id)
 static int remote_get_predecessor(node_t node, int ask_to)
 {
   int predecessor_id = -1;
-  s_task_data_t req_data;
-  char* mailbox = bprintf("%s Get Predecessor", node->mailbox);
-  req_data.answer_to = mailbox;
-  req_data.issuer_host_name = MSG_host_get_name(MSG_host_self());
+  int stop = 0;
+  char mailbox[MAILBOX_NAME_SIZE];
+  get_mailbox(ask_to, mailbox);
+  task_data_t req_data = xbt_new0(s_task_data_t, 1);
+  req_data->type = TASK_GET_PREDECESSOR;
+  get_mailbox(node->id, req_data->answer_to);
+  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
 
   // send a "Get Predecessor" request to ask_to_id
-  INFO1("Sending a 'Get Predecessor' request to %d", ask_to);
-  m_task_t task = MSG_task_create("Get Predecessor", 1000, 5000, &req_data);
-  MSG_error_t res = MSG_task_send_with_timeout(task, get_mailbox(ask_to), 20);
-
-  if (res == MSG_OK) {
+  XBT_DEBUG("Sending a 'Get Predecessor' request to %d", ask_to);
+  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",
+        task_sent, ask_to);
+    task_free(task_sent);
+  }
+  else {
 
     // receive the answer
-    task = NULL;
-    res = MSG_task_receive_with_timeout(&task, req_data.answer_to, 20);
-
-    if (res == MSG_OK) {
-
-      task_data_t ans_data;
-      ans_data = MSG_task_get_data(task);
-      predecessor_id = ans_data->answer_id;
-      INFO2("Received the answer to my 'Get Predecessor' request: the predecessor of node %d is %d", ask_to, predecessor_id);
-    }
-  }
+    XBT_DEBUG("Sent 'Get Predecessor' request (task %p) to %d, waiting for the answer on my mailbox '%s'",
+        task_sent, ask_to, req_data->answer_to);
 
-  xbt_free(mailbox);
-  return predecessor_id;
-}
+    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);
+      }
 
-/**
- * \brief Makes the current node find the predecessor node of an id.
- * \param node the current node
- * \param id the id to find
- * \return the id of the predecessor node
- */
-/*
-static int find_predecessor(node_t node, int id)
-{
-  if (node->id == node->fingers[0].id) {
-    // I am the only node in the system
-    return node->id;
-  }
+      res = MSG_comm_wait(node->comm_receive, timeout);
 
-  if (is_in_interval(id, node->id + 1, node->fingers[0].id)) {
-    return node->id;
+      if (res != MSG_OK) {
+        XBT_DEBUG("Failed to receive the answer to my 'Get Predecessor' request (task %p): %d",
+            task_sent, (int)res);
+        stop = 1;
+        MSG_comm_destroy(node->comm_receive);
+        node->comm_receive = NULL;
+      }
+      else {
+        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_active()) {
+          MC_assert(task_received == task_sent);
+          }*/
+
+        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 'Get Predecessor' request (task %p): the predecessor of node %d is %d",
+              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;
+          task_free(task_received);
+        }
+      }
+    } while (!stop);
   }
-  int ask_to = closest_preceding_node(node, id);
-  return remote_find_predecessor(node, ask_to, id);
-}
-*/
 
-/**
- * \brief Asks another node the predecessor node of an id.
- * \param node the current node
- * \param ask_to the node to ask to
- * \param id the id to find
- * \return the id of the predecessor node
- */
-/*
-static int remote_find_predecessor(node_t node, int ask_to, int id)
-{
-  s_task_data_t req_data;
-  char* mailbox = bprintf("%s Find Predecessor", node->mailbox);
-  req_data.request_id = id;
-  req_data.answer_to = mailbox;
-  req_data.issuer_host_name = MSG_host_get_name(MSG_host_self());
-
-  // send a "Find Predecessor" request to ask_to
-  INFO2("Sending a 'Find Predecessor' request to %d for key %d", ask_to, id);
-  m_task_t task = MSG_task_create("Find Predecessor", 1000, 5000, &req_data);
-  MSG_task_send(task, get_mailbox(ask_to));
-
-  // receive the answer
-  task = NULL;
-  MSG_task_receive(&task, req_data.answer_to);
-  task_data_t ans_data;
-  ans_data = MSG_task_get_data(task);
-  int predecessor = ans_data->answer_id;
-  xbt_free(mailbox);
-  INFO2("Received the answer to my 'Find Predecessor' request: the predecessor of key %d is %d", id, predecessor);
-
-  return predecessor;
+  return predecessor_id;
 }
-*/
 
 /**
  * \brief Returns the closest preceding finger of an id
@@ -851,7 +833,7 @@ static int remote_find_predecessor(node_t node, int ask_to, int id)
 int closest_preceding_node(node_t node, int id)
 {
   int i;
-  for (i = NB_BITS - 1; i >= 0; i--) {
+  for (i = nb_bits - 1; i >= 0; i--) {
     if (is_in_interval(node->fingers[i].id, node->id + 1, id - 1)) {
       return node->fingers[i].id;
     }
@@ -866,7 +848,7 @@ int closest_preceding_node(node_t node, int id)
  */
 static void stabilize(node_t node)
 {
-  INFO0("Stabilizing node");
+  XBT_DEBUG("Stabilizing node");
 
   // get the predecessor of my immediate successor
   int candidate_id;
@@ -902,7 +884,7 @@ static void notify(node_t node, int predecessor_candidate_id) {
     print_finger_table(node);
   }
   else {
-    INFO1("I don't have to change my predecessor to %d", predecessor_candidate_id);
+    XBT_DEBUG("I don't have to change my predecessor to %d", predecessor_candidate_id);
   }
 }
 
@@ -914,18 +896,18 @@ 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->request_id = predecessor_candidate_id;
-  req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
-
-  // send a "Notify" request to notify_id
-  INFO1("Sending a 'Notify' request to %d", notify_id);
-  m_task_t task = MSG_task_create("Notify", 1000, 5000, req_data);
-  char* mailbox = get_mailbox(notify_id);
-  msg_comm_t comm = MSG_task_isend(task, mailbox);
-  xbt_dynar_push(node->comms, &comm);
-  xbt_free(mailbox);
-}
+      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.
@@ -934,7 +916,7 @@ static void remote_notify(node_t node, int notify_id, int predecessor_candidate_
  */
 static void fix_fingers(node_t node) {
 
-  INFO0("Fixing fingers");
+  XBT_DEBUG("Fixing fingers");
   int i = node->next_finger_to_fix;
   int id = find_successor(node, node->id + powers2[i]);
   if (id != -1) {
@@ -943,7 +925,7 @@ static void fix_fingers(node_t node) {
       set_finger(node, i, id);
       print_finger_table(node);
     }
-    node->next_finger_to_fix = (i + 1) % NB_BITS;
+    node->next_finger_to_fix = (i + 1) % nb_bits;
   }
 }
 
@@ -954,8 +936,87 @@ static void fix_fingers(node_t node) {
  */
 static void check_predecessor(node_t node)
 {
-  INFO0("Checking whether my predecessor is alive");
-  // TODO
+  XBT_DEBUG("Checking whether my predecessor is alive");
+
+  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);
+  }
+}
+
+/**
+ * \brief Performs a find successor request to a random id.
+ * \param node the current node
+ */
+static void random_lookup(node_t node)
+{
+  
+  int id = 1337; 
+  find_successor(node, id);
+
+  /*** Random lookup disabled for tesh examples ***/
+  /*if(node->stream == NULL)
+    node->stream = RngStream_CreateStream("");
+  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);*/
+
 }
 
 /**
@@ -963,28 +1024,50 @@ static void check_predecessor(node_t node)
  */
 int main(int argc, char *argv[])
 {
+  MSG_init(&argc, argv);
   if (argc < 3) {
-    printf("Usage: %s platform_file deployment_file\n", argv[0]);
+    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);
   }
 
-  const char* platform_file = argv[1];
-  const char* application_file = argv[2];
+  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);
+      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);
+      }
+      else {
+        xbt_die("Invalid chord option '%s'", options[0]);
+      }
+    }
+    options++;
+  }
+
+  const char* platform_file = options[0];
+  const char* application_file = options[1];
 
   chord_initialize();
 
-  MSG_global_init(&argc, argv);
-  MSG_set_channel_number(0);
   MSG_create_environment(platform_file);
 
   MSG_function_register("node", node);
   MSG_launch_application(application_file);
 
-  MSG_error_t res = MSG_main();
-  INFO1("Simulation time: %g", MSG_get_clock());
+  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;