X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/3ebaa9f6d0886b21e5b01506f8136900f78e008e..6b85ea23bb4697266132fffaebc5e55ef6cc14c0:/examples/msg/chord/chord.c

diff --git a/examples/msg/chord/chord.c b/examples/msg/chord/chord.c
index a505f6c8c2..f7f145a70a 100644
--- a/examples/msg/chord/chord.c
+++ b/examples/msg/chord/chord.c
@@ -9,20 +9,30 @@
 #include "msg/msg.h"
 #include "xbt/log.h"
 #include "xbt/asserts.h"
+#include "mc/modelchecker.h"
+#include "mc/mc.h"
 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;
 
 /**
  * Finger element.
  */
 typedef struct finger {
   int id;
-  char* mailbox;
+  char mailbox[MAILBOX_NAME_SIZE]; // string representation of the id
 } s_finger_t, *finger_t;
 
 /**
@@ -30,36 +40,49 @@ typedef struct finger {
  */
 typedef struct 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()
   msg_comm_t comm_receive;                // current communication to receive
   xbt_dynar_t comms;                      // current communications being sent
+  double last_change_date;                // last time I changed a finger or my predecessor
 } s_node_t, *node_t;
 
 /**
- * Task data
+ * Types of tasks exchanged between nodes.
+ */
+typedef enum {
+  TASK_FIND_SUCCESSOR,
+  TASK_FIND_SUCCESSOR_ANSWER,
+  TASK_GET_PREDECESSOR,
+  TASK_GET_PREDECESSOR_ANSWER,
+  TASK_NOTIFY,
+  TASK_SUCCESSOR_LEAVING,
+  TASK_PREDECESSOR_LEAVING
+} e_task_type_t;
+
+/**
+ * Data attached with the tasks sent and received
  */
 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
+  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 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_data_destroy(task_data_t task_data);
 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);
@@ -70,7 +93,7 @@ static void handle_task(node_t node, m_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);
@@ -81,40 +104,41 @@ 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 random_lookup(node_t);
 static void quit_notify(node_t node, int to);
 
+/**
+ * \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;
+  DEBUG1("Sets nb_keys to %d", nb_keys);
 }
 
 /**
- * \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].
  *
- * 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]
@@ -135,11 +159,11 @@ 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;
@@ -148,12 +172,21 @@ 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 some task data.
+ * \param task_data the task data to destroy
+ */
+static void task_data_destroy(task_data_t task_data)
+{
+  xbt_free(task_data);
 }
 
 /**
@@ -162,29 +195,31 @@ 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;
+    VERB0("My finger table:");
+    VERB0("Start | Succ ");
+    for (i = 0; i < nb_bits; i++) {
+      VERB2(" %3d  | %3d ", (node->id + powers2[i]) % nb_keys, node->fingers[i].id);
+    }
+    VERB1("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();
+    DEBUG2("My new finger #%d is %d", finger_index, id);
+  }
 }
 
 /**
@@ -194,14 +229,16 @@ 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);
+    DEBUG1("My new predecessor is %d", predecessor_id);
+  }
 }
 
 /**
@@ -213,118 +250,147 @@ 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){
+    periodic_stabilize_delay = 3;
+    periodic_fix_fingers_delay = 3;
+    periodic_check_predecessor_delay = 3;
+  }
+
   double init_time = MSG_get_clock();
-  m_task_t task = NULL;
+  m_task_t task_received = NULL;
   msg_comm_t comm_send = NULL;
   int i;
   int index;
+  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;
 
   xbt_assert0(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);
+    DEBUG1("Let's sleep during %f", sleep_time);
     MSG_process_sleep(sleep_time);
-    INFO0("Hey! Let's join the system.");
+    */
+    DEBUG0("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 = NULL;
-      node.comm_receive = MSG_task_irecv(&task, node.mailbox);
-      // FIXME: do not make MSG_task_irecv() calls from several functions
-    }
+      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
+      }
 
-    if (!MSG_comm_test(node.comm_receive)) {
+      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() + 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;
+        // 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(3);
+        }
       }
       else {
-	// nothing to do: sleep for a while
-        MSG_process_sleep(5);
-      }
-    }
-    else {
-      // a transfer has occured
+        // a transfer has occured
 
-      MSG_error_t status = MSG_comm_get_status(node.comm_receive);
-      MSG_comm_destroy(node.comm_receive);
-      node.comm_receive = NULL;
+        MSG_error_t status = MSG_comm_get_status(node.comm_receive);
 
-      if (status != MSG_OK) {
-        INFO0("Failed to receive a task. Nevermind.");
+        if (status != MSG_OK) {
+          DEBUG0("Failed to receive a task. Nevermind.");
+          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);
+        }
       }
-      else {
-        // the task was successfully received
-        handle_task(&node, task);
+
+      // see if some communications are finished
+      while ((index = MSG_comm_testany(node.comms)) != -1) {
+        comm_send = xbt_dynar_get_as(node.comms, index, msg_comm_t);
+        MSG_error_t status = MSG_comm_get_status(comm_send);
+        xbt_dynar_remove_at(node.comms, index, &comm_send);
+        DEBUG3("Communication %p is finished with status %d, dynar size is now %lu",
+            comm_send, status, xbt_dynar_length(node.comms));
+	m_task_t task = MSG_comm_get_task(comm_send);
+        MSG_comm_destroy(comm_send);
+	if (status != MSG_OK) {
+	  task_data_destroy(MSG_task_get_data(task));
+	  MSG_task_destroy(task);
+	}
       }
     }
 
-    // see if some communications are finished
-    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);
-      DEBUG3("Communication %p is finished with status %d, dynar size is now %lu",
-            comm_send, MSG_comm_get_status(comm_send), xbt_dynar_length(node.comms));
+    // clean unfinished comms sent
+   /* unsigned int cursor;
+    xbt_dynar_foreach(node.comms, cursor, comm_send) {
+      m_task_t task = MSG_comm_get_task(comm_send);
+      MSG_task_cancel(task);
+      task_data_destroy(MSG_task_get_data(task));
+      MSG_task_destroy(task);
       MSG_comm_destroy(comm_send);
-    }
-  }
+      // FIXME: the task is actually not destroyed because MSG thinks that the other side (whose process is dead) is still using it
+    }*/
 
-  // clean unfinished comms sent
-  unsigned int cursor;
-  xbt_dynar_foreach(node.comms, cursor, comm_send) {
-    task = MSG_comm_get_task(comm_send);
-    MSG_task_cancel(task);
-    xbt_free(MSG_task_get_data(task));
-    MSG_task_destroy(task);
-    MSG_comm_destroy(comm_send);
+    // leave the ring
+    leave(&node);
   }
 
-  // leave the ring and stop the simulation
-  leave(&node);
+  // stop the simulation
   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);
-  }
+  xbt_free(node.fingers);
   return 0;
 }
 
@@ -336,78 +402,89 @@ int node(int argc, char *argv[])
  */
 static void handle_task(node_t node, m_task_t task) {
 
+  DEBUG1("Handling task %p", task);
   msg_comm_t comm = NULL;
-  char* mailbox = NULL;
-  const char* task_name = MSG_task_get_name(task);
+  char mailbox[MAILBOX_NAME_SIZE];
   task_data_t task_data = (task_data_t) MSG_task_get_data(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");
-      comm = MSG_task_isend(task, task_data->answer_to);
-      xbt_dynar_push(node->comms, &comm);
-      INFO3("Sending back a 'Find Successor Answer' to %s: the successor of %d is %d",
+  e_task_type_t type = task_data->type;
+
+  switch (type) {
+
+    case TASK_FIND_SUCCESSOR:
+      DEBUG2("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;
+        DEBUG4("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);
-    }
-    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 = MSG_task_isend(task, mailbox);
-      xbt_dynar_push(node->comms, &comm);
-      xbt_free(mailbox);
-    }
-  }
+        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);
+        DEBUG2("Forwarding the 'Find Successor' request for id %d to my closest preceding finger %d",
+            task_data->request_id, closest);
+        get_mailbox(closest, mailbox);
+        comm = MSG_task_isend(task, mailbox);
+        xbt_dynar_push(node->comms, &comm);
+      }
+      break;
 
-  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");
-    comm = MSG_task_isend(task, task_data->answer_to);
-    xbt_dynar_push(node->comms, &comm);
-    INFO3("Sending back a 'Get Predecessor Answer' to %s via mailbox '%s': my predecessor is %d",
+    case TASK_GET_PREDECESSOR:
+      DEBUG1("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;
+      DEBUG3("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);
-  }
-
-  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);
-    xbt_free(task_data);
-    MSG_task_destroy(task);
-  }
-
-  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);
-    xbt_free(task_data);
-    MSG_task_destroy(task);
-    /*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);
-    xbt_free(task_data);
-    MSG_task_destroy(task);
-    /* TODO
-    >> notify my new successor
-    >> update my table & predecessors table */
+      comm = MSG_task_isend(task, task_data->answer_to);
+      xbt_dynar_push(node->comms, &comm);
+      break;
+
+    case TASK_NOTIFY:
+      // someone is telling me that he may be my new predecessor
+      DEBUG1("Receiving a 'Notify' request from %s", task_data->issuer_host_name);
+      notify(node, task_data->request_id);
+      task_data_destroy(task_data);
+      MSG_task_destroy(task);
+      break;
+
+    case TASK_PREDECESSOR_LEAVING:
+      // my predecessor is about to quit
+      DEBUG1("Receiving a 'Predecessor Leaving' message from %s", task_data->issuer_host_name);
+      // modify my predecessor
+      set_predecessor(node, task_data->request_id);
+      task_data_destroy(task_data);
+      MSG_task_destroy(task);
+      /*TODO :
+      >> notify my new predecessor
+      >> send a notify_predecessors !!
+       */
+      break;
+
+    case TASK_SUCCESSOR_LEAVING:
+      // my successor is about to quit
+      DEBUG1("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_data_destroy(task_data);
+      MSG_task_destroy(task);
+      /* TODO
+      >> notify my new successor
+      >> update my table & predecessors table */
+      break;
+
+    case TASK_FIND_SUCCESSOR_ANSWER:
+    case TASK_GET_PREDECESSOR_ANSWER:
+      DEBUG2("Ignoring unexpected task of type %d (%p)", type, task);
+      task_data_destroy(task_data);
+      MSG_task_destroy(task);
+      break;
   }
 }
 
@@ -417,7 +494,7 @@ static void handle_task(node_t node, m_task_t task) {
  */
 static void create(node_t node)
 {
-  INFO0("Create a new Chord ring...");
+  DEBUG0("Create a new Chord ring...");
   set_predecessor(node, -1); // -1 means that I have no predecessor
   print_finger_table(node);
 }
@@ -427,22 +504,23 @@ 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);
   set_predecessor(node, -1); // no predecessor (yet)
 
-  int successor_id;
-  do {
-    successor_id = remote_find_successor(node, known_id, node->id);
-    if (successor_id == -1) {
-      INFO0("I really want to join the ring. Let's try again.");
-    }
-  } while (successor_id == -1);
+  int successor_id = remote_find_successor(node, known_id, node->id);
+  if (successor_id == -1) {
+    INFO0("Cannot join the ring.");
+  }
+  else {
+    set_finger(node, 0, successor_id);
+    print_finger_table(node);
+  }
 
-  set_finger(node, 0, successor_id);
-  print_finger_table(node);
+  return successor_id != -1;
 }
 
 /**
@@ -451,7 +529,7 @@ static void join(node_t node, int known_id)
  */
 static void leave(node_t node)
 {
-  INFO0("Well Guys! I Think it's time for me to quit ;)");
+  DEBUG0("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 ...
@@ -472,13 +550,14 @@ static void quit_notify(node_t node, int to)
   req_data->successor_id = node->fingers[0].id;
   req_data->pred_id = node->pred_id;
   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;
     INFO2("Telling my Successor %d about my departure via mailbox %s",
 	  node->fingers[0].id, to_mailbox);
-    task_name = "Predecessor Leaving";
+    req_data->type = TASK_PREDECESSOR_LEAVING;
   }
   else if (to == -1) {    // notify my predecessor
 
@@ -489,9 +568,9 @@ static void quit_notify(node_t node, int to)
     to_mailbox = node->pred_mailbox;
     INFO2("Telling my Predecessor %d about my departure via mailbox %s",
 	  node->pred_id, to_mailbox);
-    task_name = "Successor Leaving";
+    req_data->type = TASK_SUCCESSOR_LEAVING;
   }
-  m_task_t task = MSG_task_create(task_name, COMP_SIZE, COMM_SIZE, req_data);
+  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);
@@ -527,61 +606,76 @@ static int remote_find_successor(node_t node, int ask_to, int id)
 {
   int successor = -1;
   int stop = 0;
-  char* mailbox = get_mailbox(ask_to);
+  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;
-  req_data->answer_to =  node->mailbox;
+  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 id %d", ask_to, id);
-  m_task_t task = MSG_task_create("Find Successor", COMP_SIZE, COMM_SIZE, req_data);
-  MSG_error_t res = MSG_task_send_with_timeout(task, mailbox, 50);
+  m_task_t task_sent = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+  DEBUG3("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) {
-    INFO2("Failed to send the 'Find Successor' request to %d for id %d", ask_to, id);
-    MSG_task_destroy(task);
-    xbt_free(req_data);
+    DEBUG3("Failed to send the 'Find Successor' request (task %p) to %d for id %d",
+        task_sent, ask_to, id);
+    MSG_task_destroy(task_sent);
+    task_data_destroy(req_data);
   }
   else {
 
     // receive the answer
-    INFO2("Sent a 'Find Successor' request to %d for key %d, waiting for the answer", ask_to, id);
+    DEBUG3("Sent a 'Find Successor' request (task %p) to %d for key %d, waiting for the answer",
+        task_sent, ask_to, id);
 
     do {
       if (node->comm_receive == NULL) {
-        task = NULL;
-        node->comm_receive = MSG_task_irecv(&task, node->mailbox);
+        m_task_t task_received = NULL;
+        node->comm_receive = MSG_task_irecv(&task_received, node->mailbox);
       }
 
-      res = MSG_comm_wait(node->comm_receive, 50);
+      res = MSG_comm_wait(node->comm_receive, timeout);
 
       if (res != MSG_OK) {
-	INFO1("Failed to receive the answer to my 'Find Successor' request: %d", res);
+        DEBUG2("Failed to receive the answer to my 'Find Successor' request (task %p): %d",
+            task_sent, res);
         stop = 1;
-//      MSG_comm_destroy(node->comm_receive);
+	MSG_comm_destroy(node->comm_receive);
+	node->comm_receive = NULL;
       }
       else {
-        task = MSG_comm_get_task(node->comm_receive);
-        INFO1("Received a task '%s'", MSG_task_get_name(task));
-
-        if (strcmp(MSG_task_get_name(task), "Find Successor Answer")) {
-          handle_task(node, task);
+        m_task_t task_received = MSG_comm_get_task(node->comm_receive);
+        DEBUG1("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) {
+          // this is not the expected answer
+	  MSG_comm_destroy(node->comm_receive);
+	  node->comm_receive = NULL;
+          handle_task(node, task_received);
         }
         else {
-          INFO2("This is the answer to my 'Find Successor' request: the successor of key %d is %d", id, successor);
-          task_data_t ans_data = MSG_task_get_data(task);
+          // this is our answer
+          DEBUG4("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_task_destroy(task);
-          xbt_free(req_data);
+	  MSG_comm_destroy(node->comm_receive);
+	  node->comm_receive = NULL;
+          MSG_task_destroy(task_received);
+          task_data_destroy(req_data);
         }
       }
-      node->comm_receive = NULL;
     } while (!stop);
   }
 
-  xbt_free(mailbox);
   return successor;
 }
 
@@ -596,60 +690,72 @@ static int remote_get_predecessor(node_t node, int ask_to)
 {
   int predecessor_id = -1;
   int stop = 0;
-  char* mailbox = get_mailbox(ask_to);
+  char mailbox[MAILBOX_NAME_SIZE];
+  get_mailbox(ask_to, mailbox);
   task_data_t req_data = xbt_new0(s_task_data_t, 1);
-  req_data->answer_to = node->mailbox;
+  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", COMP_SIZE, COMM_SIZE, req_data);
-  MSG_error_t res = MSG_task_send_with_timeout(task, mailbox, 50);
+  DEBUG1("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);
 
   if (res != MSG_OK) {
-    INFO1("Failed to send the 'Get Predecessor' request to %d", ask_to);
-    MSG_task_destroy(task);
-    xbt_free(req_data);
+    DEBUG2("Failed to send the 'Get Predecessor' request (task %p) to %d",
+        task_sent, ask_to);
+    MSG_task_destroy(task_sent);
+    task_data_destroy(req_data);
   }
   else {
 
     // receive the answer
-    INFO2("Sent 'Get Predecessor' request to %d, waiting for the answer on my mailbox '%s'", ask_to, req_data->answer_to);
+    DEBUG3("Sent 'Get Predecessor' request (task %p) to %d, waiting for the answer on my mailbox '%s'",
+        task_sent, ask_to, req_data->answer_to);
 
     do {
       if (node->comm_receive == NULL) { // FIXME simplify this
-        task = NULL;
-        node->comm_receive = MSG_task_irecv(&task, node->mailbox);
+        m_task_t task_received = NULL;
+        node->comm_receive = MSG_task_irecv(&task_received, node->mailbox);
       }
 
-      res = MSG_comm_wait(node->comm_receive, 50);
+      res = MSG_comm_wait(node->comm_receive, timeout);
 
       if (res != MSG_OK) {
-        INFO1("Failed to receive the answer to my 'Get Predecessor' request: %d", res);
+        DEBUG2("Failed to receive the answer to my 'Get Predecessor' request (task %p): %d",
+            task_sent, res);
         stop = 1;
-//        MSG_comm_destroy(node->comm_receive);
+	MSG_comm_destroy(node->comm_receive);
+	node->comm_receive = NULL;
       }
       else {
-        task = MSG_comm_get_task(node->comm_receive);
-        INFO1("Received a task '%s'", MSG_task_get_name(task));
+        m_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 (strcmp(MSG_task_get_name(task), "Get Predecessor Answer")) {
-          handle_task(node, task);
+        if (task_received != task_sent) {
+	  MSG_comm_destroy(node->comm_receive);
+	  node->comm_receive = NULL;
+          handle_task(node, task_received);
         }
         else {
-          INFO2("This is the answer to my 'Get Predecessor' request: the predecessor of node %d is %d", ask_to, predecessor_id);
-          task_data_t ans_data = MSG_task_get_data(task);
+          DEBUG3("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_task_destroy(task);
-          xbt_free(req_data);
+	  MSG_comm_destroy(node->comm_receive);
+	  node->comm_receive = NULL;
+          MSG_task_destroy(task_received);
+          task_data_destroy(req_data);
         }
       }
-      node->comm_receive = NULL;
     } while (!stop);
   }
 
-  xbt_free(mailbox);
   return predecessor_id;
 }
 
@@ -663,7 +769,7 @@ static int remote_get_predecessor(node_t node, int ask_to)
 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;
     }
@@ -678,7 +784,7 @@ int closest_preceding_node(node_t node, int id)
  */
 static void stabilize(node_t node)
 {
-  INFO0("Stabilizing node");
+  DEBUG0("Stabilizing node");
 
   // get the predecessor of my immediate successor
   int candidate_id;
@@ -714,7 +820,7 @@ 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);
+    DEBUG1("I don't have to change my predecessor to %d", predecessor_candidate_id);
   }
 }
 
@@ -727,16 +833,17 @@ 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
-  INFO1("Sending a 'Notify' request to %d", notify_id);
-  m_task_t task = MSG_task_create("Notify", COMP_SIZE, COMM_SIZE, req_data);
-  char* mailbox = get_mailbox(notify_id);
+  m_task_t task = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
+  DEBUG2("Sending a 'Notify' request (task %p) to %d", task, notify_id);
+  char mailbox[MAILBOX_NAME_SIZE];
+  get_mailbox(notify_id, mailbox);
   msg_comm_t comm = MSG_task_isend(task, mailbox);
   xbt_dynar_push(node->comms, &comm);
-  xbt_free(mailbox);
 }
 
 /**
@@ -746,7 +853,7 @@ static void remote_notify(node_t node, int notify_id, int predecessor_candidate_
  */
 static void fix_fingers(node_t node) {
 
-  INFO0("Fixing fingers");
+  DEBUG0("Fixing fingers");
   int i = node->next_finger_to_fix;
   int id = find_successor(node, node->id + powers2[i]);
   if (id != -1) {
@@ -755,7 +862,7 @@ 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;
   }
 }
 
@@ -766,27 +873,61 @@ static void fix_fingers(node_t node) {
  */
 static void check_predecessor(node_t node)
 {
-  INFO0("Checking whether my predecessor is alive");
+  DEBUG0("Checking whether my predecessor is alive");
   // TODO
 }
 
+/**
+ * \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; // TODO pick a pseudorandom id
+  DEBUG1("Making a lookup request for id %d", id);
+  find_successor(node, id);
+}
+
 /**
  * \brief Main function.
  */
 int main(int argc, char *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];
+  MSG_global_init(&argc, argv);
+
+  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);
+      DEBUG1("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);
+	DEBUG1("Set timeout to %d", timeout);
+      }
+      else {
+	xbt_assert1(0, "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);