X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/blobdiff_plain/b02ac1c736917a89bec0baa4de9afc17cd29777c..030e7d63a2fc3a0f82f5c820e1d0ac02d2021ba2:/examples/msg/chord/chord.c

diff --git a/examples/msg/chord/chord.c b/examples/msg/chord/chord.c
index fe9ab9d15a..6787b2d103 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;
 
 /**
@@ -30,13 +40,13 @@ 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;
 
 /**
@@ -60,17 +70,18 @@ typedef struct task_data {
   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)
-  const char* answer_to;                  // mailbox to send an answer to
+  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);
@@ -92,6 +103,7 @@ 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);
 
 /**
@@ -100,35 +112,32 @@ static void quit_notify(node_t node, int to);
 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]
@@ -149,11 +158,11 @@ 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;
@@ -162,11 +171,21 @@ 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
+ * \param mailbox pointer to where the mailbox name should be written
+ * (there must be enough space)
+ */
+static void get_mailbox(int node_id, char* mailbox)
+{
+  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 char* get_mailbox(int node_id)
+static void task_data_destroy(task_data_t task_data)
 {
-  return bprintf("mailbox%d", node_id);
+  xbt_free(task_data);
 }
 
 /**
@@ -175,29 +194,31 @@ 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);
-  DEBUG2("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);
+  }
 }
 
 /**
@@ -207,14 +228,16 @@ 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();
 
-  DEBUG1("My new predecessor is %d", predecessor_id);
+    DEBUG1("My new predecessor is %d", predecessor_id);
+  }
 }
 
 /**
@@ -226,28 +249,35 @@ 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 = 8;
+    periodic_fix_fingers_delay = 8;
+    periodic_check_predecessor_delay = 8;
+  }
+
   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);
   }
 
@@ -258,19 +288,23 @@ int node(int argc, char *argv[])
   }
   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
     DEBUG1("Let's sleep during %f", sleep_time);
     MSG_process_sleep(sleep_time);
+    */
     DEBUG0("Hey! Let's join the system.");
 
     join_success = join(&node, known_id);
   }
 
   if (join_success) {
-    while (MSG_get_clock() < init_time + deadline) {
+    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;
@@ -283,16 +317,20 @@ int node(int argc, char *argv[])
         // no task was received: make some periodic calls
         if (MSG_get_clock() >= next_stabilize_date) {
           stabilize(&node);
-          next_stabilize_date = MSG_get_clock() + 10;
+          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() + 10;
+          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() + 10;
+          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);
@@ -302,51 +340,54 @@ int node(int argc, char *argv[])
         // 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;
 
         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);
         }
       }
 
       // 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);
+	}
       }
+      */
     }
 
     // clean unfinished comms sent
-    unsigned int cursor;
+   /* unsigned int cursor;
     xbt_dynar_foreach(node.comms, cursor, comm_send) {
-      task = MSG_comm_get_task(comm_send);
+      m_task_t task = MSG_comm_get_task(comm_send);
       MSG_task_cancel(task);
-      xbt_free(MSG_task_get_data(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
-    }
+    }*/
 
     // leave the ring
     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;
 }
 
@@ -359,8 +400,7 @@ 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;
+  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;
 
@@ -373,21 +413,19 @@ static void handle_task(node_t node, m_task_t task) {
       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;
-        comm = MSG_task_isend(task, task_data->answer_to);
-        xbt_dynar_push(node->comms, &comm);
-        DEBUG3("Sending back a 'Find Successor Answer' to %s: the successor of %d is %d",
+        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);
+        MSG_task_dsend(task, task_data->answer_to);
       }
       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);
-        mailbox = get_mailbox(closest);
-        comm = MSG_task_isend(task, mailbox);
-        xbt_dynar_push(node->comms, &comm);
-        xbt_free(mailbox);
+        get_mailbox(closest, mailbox);
+        MSG_task_dsend(task, mailbox);
       }
       break;
 
@@ -395,18 +433,17 @@ static void handle_task(node_t node, m_task_t task) {
       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;
-      comm = MSG_task_isend(task, task_data->answer_to);
-      xbt_dynar_push(node->comms, &comm);
       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);
+      MSG_task_dsend(task, task_data->answer_to);
       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);
-      xbt_free(task_data);
+      task_data_destroy(task_data);
       MSG_task_destroy(task);
       break;
 
@@ -415,7 +452,7 @@ static void handle_task(node_t node, m_task_t task) {
       DEBUG1("Receiving a 'Predecessor Leaving' message from %s", task_data->issuer_host_name);
       // modify my predecessor
       set_predecessor(node, task_data->request_id);
-      xbt_free(task_data);
+      task_data_destroy(task_data);
       MSG_task_destroy(task);
       /*TODO :
       >> notify my new predecessor
@@ -428,16 +465,19 @@ static void handle_task(node_t node, m_task_t task) {
       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);
-      xbt_free(task_data);
+      task_data_destroy(task_data);
       MSG_task_destroy(task);
       /* TODO
       >> notify my new successor
       >> update my table & predecessors table */
       break;
 
-    default:
-      CRITICAL1("Received an unexpected task: %d", type);
-      //xbt_abort();
+    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;
   }
 }
 
@@ -466,7 +506,7 @@ static int join(node_t node, int known_id)
 
   int successor_id = remote_find_successor(node, known_id, node->id);
   if (successor_id == -1) {
-    DEBUG0("Cannot join the ring.");
+    INFO0("Cannot join the ring.");
   }
   else {
     set_finger(node, 0, successor_id);
@@ -503,6 +543,7 @@ 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
@@ -558,63 +599,76 @@ 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
-  m_task_t task = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, req_data);
-  DEBUG3("Sending a 'Find Successor' request (task %p) to %d for id %d", task, ask_to, id);
-  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) {
-    DEBUG2("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
     DEBUG3("Sent a 'Find Successor' request (task %p) to %d for key %d, waiting for the answer",
-        task, ask_to, id);
+        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) {
-        DEBUG2("Failed to receive the answer to my 'Find Successor' request (task %p): %d", task, 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);
-        task_data_t ans_data = MSG_task_get_data(task);
-
-        if (ans_data->type != 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 {
-          DEBUG3("Received the answer to my 'Find Successor' request (task %p): the successor of key %d is %d",
-              task, id, successor);
+          // 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;
 }
 
@@ -629,60 +683,72 @@ 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->type = TASK_GET_PREDECESSOR;
-  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 "Get Predecessor" request to ask_to_id
   DEBUG1("Sending a 'Get Predecessor' request to %d", ask_to);
-  m_task_t task = MSG_task_create(NULL, 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);
+  MSG_error_t res = MSG_task_send_with_timeout(task_sent, mailbox, timeout);
 
   if (res != MSG_OK) {
-    DEBUG1("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
-    DEBUG2("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) {
-        DEBUG1("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);
-        task_data_t ans_data = MSG_task_get_data(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 (ans_data->type != 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 {
-          DEBUG2("Received the answer to my 'Get Predecessor' request: the predecessor of node %d is %d", ask_to, predecessor_id);
+          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;
 }
 
@@ -696,7 +762,7 @@ 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;
     }
@@ -765,12 +831,11 @@ static void remote_notify(node_t node, int notify_id, int predecessor_candidate_
   req_data->issuer_host_name = MSG_host_get_name(MSG_host_self());
 
   // send a "Notify" request to notify_id
-  DEBUG1("Sending a 'Notify' request to %d", notify_id);
   m_task_t task = MSG_task_create(NULL, COMP_SIZE, COMM_SIZE, 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);
+  DEBUG2("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);
 }
 
 /**
@@ -789,7 +854,7 @@ 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;
   }
 }
 
@@ -804,23 +869,57 @@ static void check_predecessor(node_t node)
   // 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);