-only trigger check config if we actually need it
[oweals/gnunet.git] / src / statistics / gnunet-service-statistics.c
index efc6ce12890b440dc6dea51c53651c9bdc58c1a6..8d989dafbeed061a25b51fffee74562499ffd521 100644 (file)
@@ -1,10 +1,10 @@
 /*
      This file is part of GNUnet.
-     (C) 2009 Christian Grothoff (and other contributing authors)
+     Copyright (C) 2009, 2010, 2012, 2014 GNUnet e.V.
 
      GNUnet is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published
-     by the Free Software Foundation; either version 2, or (at your
+     by the Free Software Foundation; either version 3, or (at your
      option) any later version.
 
      GNUnet is distributed in the hope that it will be useful, but
 
      You should have received a copy of the GNU General Public License
      along with GNUnet; see the file COPYING.  If not, write to the
-     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-     Boston, MA 02111-1307, USA.
+     Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+     Boston, MA 02110-1301, USA.
 */
 
 /**
  * @file statistics/gnunet-service-statistics.c
  * @brief program that tracks statistics
  * @author Christian Grothoff
- * 
- * TODO:
- * - use BIO for IO operations
  */
 #include "platform.h"
+#include "gnunet_bio_lib.h"
+#include "gnunet_container_lib.h"
 #include "gnunet_disk_lib.h"
 #include "gnunet_getopt_lib.h"
 #include "gnunet_protocols.h"
 #include "gnunet_time_lib.h"
 #include "statistics.h"
 
+/**
+ * Watch entry.
+ */
+struct WatchEntry
+{
+
+  /**
+   * Watch entries are kept in a linked list.
+   */
+  struct WatchEntry *next;
+
+  /**
+   * Watch entries are kept in a linked list.
+   */
+  struct WatchEntry *prev;
+
+  /**
+   * For which client is this watch entry?
+   */
+  struct GNUNET_SERVER_Client *client;
+
+  /**
+   * Last value we communicated to the client for this watch entry.
+   */
+  uint64_t last_value;
+
+  /**
+   * Unique watch number for this client and this watched value.
+   */
+  uint32_t wid;
+
+  /**
+   * Is last_value valid
+   * #GNUNET_NO : last_value is n/a, #GNUNET_YES: last_value is valid
+   */
+  int last_value_set;
+
+};
+
+
+/**
+ * We keep the statistics organized by subsystem for faster
+ * lookup during SET operations.
+ */
+struct SubsystemEntry;
+
+
 /**
  * Entry in the statistics list.
  */
@@ -47,23 +93,30 @@ struct StatsEntry
   struct StatsEntry *next;
 
   /**
-   * Name of the service, points into the
-   * middle of msg.
+   * This is a linked list.
    */
-  const char *service;
+  struct StatsEntry *prev;
 
   /**
-   * Name for the value, points into
-   * the middle of msg.
+   * Subsystem this entry belongs to.
    */
-  const char *name;
+  struct SubsystemEntry *subsystem;
 
   /**
-   * Message that can be used to set this value,
-   * stored at the end of the memory used by
+   * Name for the value stored by this entry, allocated at the end of
    * this struct.
    */
-  struct GNUNET_STATISTICS_SetMessage *msg;
+  const char *name;
+
+  /**
+   * Watch context for changes to this value, or NULL for none.
+   */
+  struct WatchEntry *we_head;
+
+  /**
+   * Watch context for changes to this value, or NULL for none.
+   */
+  struct WatchEntry *we_tail;
 
   /**
    * Our value.
@@ -80,17 +133,102 @@ struct StatsEntry
    */
   int persistent;
 
+  /**
+   * Is this value set?
+   * #GNUNET_NO: value is n/a, #GNUNET_YES: value is valid
+   */
+  int set;
+
+};
+
+
+/**
+ * We keep the statistics organized by subsystem for faster
+ * lookup during SET operations.
+ */
+struct SubsystemEntry
+{
+  /**
+   * Subsystems are kept in a DLL.
+   */
+  struct SubsystemEntry *next;
+
+  /**
+   * Subsystems are kept in a DLL.
+   */
+  struct SubsystemEntry *prev;
+
+  /**
+   * Head of list of values kept for this subsystem.
+   */
+  struct StatsEntry *stat_head;
+
+  /**
+   * Tail of list of values kept for this subsystem.
+   */
+  struct StatsEntry *stat_tail;
+
+  /**
+   * Name of the subsystem this entry is for, allocated at
+   * the end of this struct, do not free().
+   */
+  const char *service;
+
 };
 
+
+/**
+ * Client entry.
+ */
+struct ClientEntry
+{
+  /**
+   * Corresponding server handle.
+   */
+  struct GNUNET_SERVER_Client *client;
+
+  /**
+   * Which subsystem is this client writing to (SET/UPDATE)?
+   */
+  struct SubsystemEntry *subsystem;
+
+  /**
+   * Maximum watch ID used by this client so far.
+   */
+  uint32_t max_wid;
+
+};
+
+
 /**
  * Our configuration.
  */
 static const struct GNUNET_CONFIGURATION_Handle *cfg;
 
 /**
- * Linked list of our active statistics.
+ * Head of linked list of subsystems with active statistics.
  */
-static struct StatsEntry *start;
+static struct SubsystemEntry *sub_head;
+
+/**
+ * Tail of linked list of subsystems with active statistics.
+ */
+static struct SubsystemEntry *sub_tail;
+
+/**
+ * Number of connected clients.
+ */
+static unsigned int client_count;
+
+/**
+ * Handle to our server.
+ */
+static struct GNUNET_SERVER_Handle *srv;
+
+/**
+ * Our notification context.
+ */
+static struct GNUNET_SERVER_NotificationContext *nc;
 
 /**
  * Counter used to generate unique values.
@@ -98,9 +236,33 @@ static struct StatsEntry *start;
 static uint32_t uidgen;
 
 /**
- * Load persistent values from disk.  Disk format is
- * exactly the same format that we also use for
- * setting the values over the network.
+ * Set to #GNUNET_YES if we are shutting down as soon as possible.
+ */
+static int in_shutdown;
+
+
+/**
+ * Inject a message to our server with a client of 'NULL'.
+ *
+ * @param cls the `struct GNUNET_SERVER_Handle`
+ * @param client unused
+ * @param msg message to inject
+ */
+static int
+inject_message (void *cls,
+                void *client,
+                const struct GNUNET_MessageHeader *msg)
+{
+  struct GNUNET_SERVER_Handle *server = cls;
+
+  GNUNET_break (GNUNET_OK == GNUNET_SERVER_inject (server, NULL, msg));
+  return GNUNET_OK;
+}
+
+
+/**
+ * Load persistent values from disk.  Disk format is exactly the same
+ * format that we also use for setting the values over the network.
  *
  * @param server handle to the server context
  */
@@ -108,120 +270,190 @@ static void
 load (struct GNUNET_SERVER_Handle *server)
 {
   char *fn;
-  struct GNUNET_DISK_FileHandle *fh;
-  struct GNUNET_DISK_MapHandle *mh;
-  struct stat sb;
+  struct GNUNET_BIO_ReadHandle *rh;
+  uint64_t fsize;
   char *buf;
-  size_t off;
-  const struct GNUNET_MessageHeader *msg;
+  struct GNUNET_SERVER_MessageStreamTokenizer *mst;
 
-  fn = GNUNET_DISK_get_home_filename (cfg,
-                                      "statistics", "statistics.data", NULL);
-  if (fn == NULL)
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_filename (cfg,
+                                               "STATISTICS",
+                                               "DATABASE",
+                                               &fn))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "STATISTICS",
+                               "DATABASE");
     return;
-  if ((0 != stat (fn, &sb)) || (sb.st_size == 0))
-    {
-      GNUNET_free (fn);
-      return;
-    }
-  fh = GNUNET_DISK_file_open (fn, GNUNET_DISK_OPEN_READ,
-                             GNUNET_DISK_PERM_NONE);
-  if (!fh)
-    {
-      GNUNET_free (fn);
-      return;
-    }
-  buf = GNUNET_DISK_file_map (fh, &mh, GNUNET_DISK_MAP_TYPE_READ, sb.st_size);
-  if (NULL == buf)
-    {
-      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING, "mmap", fn);
-      GNUNET_break (GNUNET_OK == GNUNET_DISK_file_close (fh));
-      GNUNET_free (fn);
-      return;
-    }
+  }
+  if ( (GNUNET_OK !=
+        GNUNET_DISK_file_size (fn,
+                               &fsize,
+                               GNUNET_NO,
+                               GNUNET_YES)) ||
+       (0 == fsize) )
+  {
+    GNUNET_free (fn);
+    return;
+  }
+  buf = GNUNET_malloc (fsize);
+  rh = GNUNET_BIO_read_open (fn);
+  if (!rh)
+  {
+    GNUNET_free (buf);
+    GNUNET_free (fn);
+    return;
+  }
+  if (GNUNET_OK !=
+      GNUNET_BIO_read (rh,
+                       fn,
+                       buf,
+                       fsize))
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                              "read",
+                              fn);
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_BIO_read_close (rh, NULL));
+    GNUNET_free (buf);
+    GNUNET_free (fn);
+    return;
+  }
   GNUNET_log (GNUNET_ERROR_TYPE_INFO,
               _("Loading %llu bytes of statistics from `%s'\n"),
-              (unsigned long long) sb.st_size, fn);
-  off = 0;
-  while (off + sizeof (struct GNUNET_MessageHeader) < sb.st_size)
-    {
-      msg = (const struct GNUNET_MessageHeader *) &buf[off];
-      if ((ntohs (msg->size) + off > sb.st_size) ||
-          (GNUNET_OK != GNUNET_SERVER_inject (server, NULL, msg)))
-        {
-          GNUNET_break (0);
-          break;
-        }
-      off += ntohs (msg->size);
-    }
-  GNUNET_break (GNUNET_OK == GNUNET_DISK_file_unmap (mh));
-  GNUNET_break (GNUNET_OK == GNUNET_DISK_file_close (fh));
+              (unsigned long long) fsize, fn);
+  mst = GNUNET_SERVER_mst_create (&inject_message,
+                                  server);
+  GNUNET_break (GNUNET_OK ==
+                GNUNET_SERVER_mst_receive (mst, NULL,
+                                           buf, fsize,
+                                           GNUNET_YES,
+                                           GNUNET_NO));
+  GNUNET_SERVER_mst_destroy (mst);
+  GNUNET_free (buf);
+  GNUNET_break (GNUNET_OK ==
+                GNUNET_BIO_read_close (rh,
+                                       NULL));
   GNUNET_free (fn);
 }
 
+
 /**
  * Write persistent statistics to disk.
  */
 static void
-save ()       
+save ()
 {
+  struct SubsystemEntry *se;
   struct StatsEntry *pos;
   char *fn;
-  struct GNUNET_DISK_FileHandle *fh;
+  struct GNUNET_BIO_WriteHandle *wh;
   uint16_t size;
   unsigned long long total;
+  size_t nlen;
+  size_t slen;
+  struct GNUNET_STATISTICS_SetMessage *msg;
 
-  fh = NULL;
-  fn = GNUNET_DISK_get_home_filename (cfg,
-                                      "statistics", "statistics.data", NULL);
-  if (fn != NULL)
-    fh = GNUNET_DISK_file_open (fn, GNUNET_DISK_OPEN_WRITE
-        | GNUNET_DISK_OPEN_CREATE | GNUNET_DISK_OPEN_TRUNCATE,
-        GNUNET_DISK_PERM_USER_READ | GNUNET_DISK_PERM_USER_WRITE);
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_filename (cfg,
+                                               "STATISTICS",
+                                               "DATABASE",
+                                               &fn))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "STATISTICS",
+                               "DATABASE");
+    return;
+  }
+  (void) GNUNET_DISK_directory_create_for_file (fn);
+  wh = GNUNET_BIO_write_open (fn);
   total = 0;
-  while (NULL != (pos = start))
+  while (NULL != (se = sub_head))
+  {
+    GNUNET_CONTAINER_DLL_remove (sub_head,
+                                 sub_tail,
+                                 se);
+    slen = strlen (se->service) + 1;
+    while (NULL != (pos = se->stat_head))
     {
-      start = pos->next;
-      if ((pos->persistent) && (NULL != fh))
+      GNUNET_CONTAINER_DLL_remove (se->stat_head,
+                                   se->stat_tail,
+                                   pos);
+      if ((pos->persistent) && (NULL != wh))
+      {
+        nlen = strlen (pos->name) + 1;
+        size = sizeof (struct GNUNET_STATISTICS_SetMessage) + nlen + slen;
+        GNUNET_assert (size < UINT16_MAX);
+        msg = GNUNET_malloc (size);
+
+        msg->header.size = htons ((uint16_t) size);
+        msg->header.type = htons (GNUNET_MESSAGE_TYPE_STATISTICS_SET);
+        GNUNET_assert (nlen + slen ==
+                       GNUNET_STRINGS_buffer_fill ((char *) &msg[1],
+                                                   nlen + slen,
+                                                   2,
+                                                   se->service,
+                                                   pos->name));
+        msg->flags = htonl (pos->persistent ? GNUNET_STATISTICS_SETFLAG_PERSISTENT : 0);
+        msg->value = GNUNET_htonll (pos->value);
+        if (GNUNET_OK != GNUNET_BIO_write (wh,
+                                           msg,
+                                           size))
+        {
+          GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                    "write",
+                                    fn);
+          if (GNUNET_OK != GNUNET_BIO_write_close (wh))
+            GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                      "close",
+                                      fn);
+          wh = NULL;
+        }
+        else
         {
-          size = htons (pos->msg->header.size);
-          if (size != GNUNET_DISK_file_write (fh, pos->msg, size))
-            {
-              GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
-                                        "write", fn);
-              GNUNET_DISK_file_close (fh);
-             fh = NULL;
-            }
-          else
-            total += size;
+          total += size;
         }
+        GNUNET_free (msg);
+      }
       GNUNET_free (pos);
     }
-  if (NULL != fh)
-    {
-      GNUNET_DISK_file_close (fh);
-      if (total == 0)
-        GNUNET_break (0 == UNLINK (fn));
-      else
-        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
-                    _("Wrote %llu bytes of statistics to `%s'\n"), total, fn);
-    }
+    GNUNET_free (se);
+  }
+  if (NULL != wh)
+  {
+    if (GNUNET_OK !=
+        GNUNET_BIO_write_close (wh))
+      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                "close",
+                                fn);
+    if (0 == total)
+      GNUNET_break (0 ==
+                    UNLINK (fn));
+    else
+      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                  _("Wrote %llu bytes of statistics to `%s'\n"),
+                  total,
+                  fn);
+  }
   GNUNET_free_non_null (fn);
 }
 
 
 /**
  * Transmit the given stats value.
+ *
+ * @param client receiver of the value
+ * @param e value to transmit
  */
 static void
-transmit (struct GNUNET_SERVER_TransmitContext *tc,
+transmit (struct GNUNET_SERVER_Client *client,
           const struct StatsEntry *e)
 {
   struct GNUNET_STATISTICS_ReplyMessage *m;
   size_t size;
 
-  size =
-    sizeof (struct GNUNET_STATISTICS_ReplyMessage) + strlen (e->service) + 1 +
+  size = sizeof (struct GNUNET_STATISTICS_ReplyMessage) +
+    strlen (e->subsystem->service) + 1 +
     strlen (e->name) + 1;
   GNUNET_assert (size < GNUNET_SERVER_MAX_MESSAGE_SIZE);
   m = GNUNET_malloc (size);
@@ -232,28 +464,50 @@ transmit (struct GNUNET_SERVER_TransmitContext *tc,
     m->uid |= htonl (GNUNET_STATISTICS_PERSIST_BIT);
   m->value = GNUNET_htonll (e->value);
   size -= sizeof (struct GNUNET_STATISTICS_ReplyMessage);
-  GNUNET_assert (size == GNUNET_STRINGS_buffer_fill ((char *) &m[1],
-                                                     size,
-                                                     2, e->service, e->name));
-#if DEBUG_STATISTICS
+  GNUNET_assert (size ==
+                 GNUNET_STRINGS_buffer_fill ((char *) &m[1],
+                                             size,
+                                             2,
+                                             e->subsystem->service,
+                                             e->name));
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-              "Transmitting value for `%s:%s': %llu\n",
-              e->service, e->name, e->value);
-#endif
-  GNUNET_SERVER_transmit_context_append_message (tc, &m->header);
+              "Transmitting value for `%s:%s' (%d): %llu\n",
+              e->subsystem->service,
+              e->name,
+              e->persistent,
+              (unsigned long long) e->value);
+  GNUNET_SERVER_notification_context_unicast (nc, client, &m->header,
+                                              GNUNET_NO);
   GNUNET_free (m);
 }
 
 
 /**
- * Does this entry match the request?
+ * Find a client entry for the given client handle, or create one.
+ *
+ * @param client handle to match
+ * @return corresponding client entry struct
  */
-static int
-matches (const struct StatsEntry *e, const char *service, const char *name)
+static struct ClientEntry *
+make_client_entry (struct GNUNET_SERVER_Client *client)
 {
-  return ((0 == strlen (service)) ||
-          (0 == strcmp (service, e->service)))
-    && ((0 == strlen (name)) || (0 == strcmp (name, e->name)));
+  struct ClientEntry *ce;
+
+  ce = GNUNET_SERVER_client_get_user_context (client,
+                                              struct ClientEntry);
+  if (NULL != ce)
+    return ce;
+  if (NULL == nc)
+  {
+    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
+    return NULL;
+  }
+  ce = GNUNET_new (struct ClientEntry);
+  ce->client = client;
+  GNUNET_SERVER_client_set_user_context (client, ce);
+  client_count++;
+  GNUNET_SERVER_notification_context_add (nc, client);
+  return ce;
 }
 
 
@@ -263,44 +517,173 @@ matches (const struct StatsEntry *e, const char *service, const char *name)
  * @param cls closure
  * @param client identification of the client
  * @param message the actual message
- * @return GNUNET_OK to keep the connection open,
- *         GNUNET_SYSERR to close it (signal serious error)
+ * @return #GNUNET_OK to keep the connection open,
+ *         #GNUNET_SYSERR to close it (signal serious error)
  */
 static void
 handle_get (void *cls,
             struct GNUNET_SERVER_Client *client,
             const struct GNUNET_MessageHeader *message)
 {
-  char *service;
-  char *name;
+  struct GNUNET_MessageHeader end;
+  const char *service;
+  const char *name;
+  size_t slen;
+  size_t nlen;
+  struct SubsystemEntry *se;
   struct StatsEntry *pos;
-  struct GNUNET_SERVER_TransmitContext *tc;
   size_t size;
 
+  if (NULL == make_client_entry (client))
+    return; /* new client during shutdown */
   size = ntohs (message->size) - sizeof (struct GNUNET_MessageHeader);
-  if (size != GNUNET_STRINGS_buffer_tokenize ((const char *) &message[1],
-                                              size, 2, &service, &name))
-    {
-      GNUNET_break (0);
-      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
-      return;
-    }
-#if DEBUG_STATISTICS
+  if (size !=
+      GNUNET_STRINGS_buffer_tokenize ((const char *) &message[1],
+                                      size,
+                                      2,
+                                      &service,
+                                      &name))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  slen = strlen (service);
+  nlen = strlen (name);
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "Received request for statistics on `%s:%s'\n",
-              strlen (service) ? service : "*", strlen (name) ? name : "*");
-#endif
-  tc = GNUNET_SERVER_transmit_context_create (client);
-  pos = start;
-  while (pos != NULL)
+              slen ? service : "*",
+              nlen ? name : "*");
+  for (se = sub_head; NULL != se; se = se->next)
+  {
+    if (! ( (0 == slen) ||
+            (0 == strcmp (service, se->service))) )
+      continue;
+    for (pos = se->stat_head; NULL != pos; pos = pos->next)
     {
-      if (matches (pos, service, name))
-        transmit (tc, pos);
-      pos = pos->next;
+      if  (! ( (0 == nlen) ||
+               (0 == strcmp (name, pos->name))) )
+        continue;
+      transmit (client, pos);
     }
-  GNUNET_SERVER_transmit_context_append_data (tc, NULL, 0,
-                                             GNUNET_MESSAGE_TYPE_STATISTICS_END);
-  GNUNET_SERVER_transmit_context_run (tc, GNUNET_TIME_UNIT_FOREVER_REL);
+  }
+  end.size = htons (sizeof (struct GNUNET_MessageHeader));
+  end.type = htons (GNUNET_MESSAGE_TYPE_STATISTICS_END);
+  GNUNET_SERVER_notification_context_unicast (nc,
+                                              client,
+                                              &end,
+                                              GNUNET_NO);
+  GNUNET_SERVER_receive_done (client, GNUNET_OK);
+}
+
+
+/**
+ * Notify all clients listening about a change to a value.
+ *
+ * @param se value that changed
+ */
+static void
+notify_change (struct StatsEntry *se)
+{
+  struct GNUNET_STATISTICS_WatchValueMessage wvm;
+  struct WatchEntry *pos;
+
+  for (pos = se->we_head; NULL != pos; pos = pos->next)
+  {
+    if (GNUNET_YES == pos->last_value_set)
+    {
+      if (pos->last_value == se->value)
+        continue;
+    }
+    else
+    {
+      pos->last_value_set = GNUNET_YES;
+    }
+    wvm.header.type = htons (GNUNET_MESSAGE_TYPE_STATISTICS_WATCH_VALUE);
+    wvm.header.size =
+      htons (sizeof (struct GNUNET_STATISTICS_WatchValueMessage));
+    wvm.flags = htonl (se->persistent ? GNUNET_STATISTICS_SETFLAG_PERSISTENT : 0);
+    wvm.wid = htonl (pos->wid);
+    wvm.reserved = htonl (0);
+    wvm.value = GNUNET_htonll (se->value);
+    GNUNET_SERVER_notification_context_unicast (nc,
+                                                pos->client,
+                                                &wvm.header,
+                                               GNUNET_NO);
+    pos->last_value = se->value;
+  }
+}
+
+
+/**
+ * Find the subsystem entry of the given name for the specified client.
+ *
+ * @param ce client looking for the subsystem, may contain a hint
+ *           to find the entry faster, can be NULL
+ * @param service name of the subsystem to look for
+ * @return subsystem entry, never NULL (subsystem entry is created if necessary)
+ */
+static struct SubsystemEntry *
+find_subsystem_entry (struct ClientEntry *ce,
+                      const char *service)
+{
+  size_t slen;
+  struct SubsystemEntry *se;
+
+  if (NULL != ce)
+    se = ce->subsystem;
+  else
+    se = NULL;
+  if ( (NULL == se) ||
+       (0 != strcmp (service,
+                     se->service)) )
+  {
+    for (se = sub_head; NULL != se; se = se->next)
+      if (0 == strcmp (service,
+                       se->service))
+        break;
+    if (NULL != ce)
+      ce->subsystem = se;
+  }
+  if (NULL != se)
+    return se;
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Allocating new subsystem entry `%s'\n",
+              service);
+  slen = strlen (service) + 1;
+  se = GNUNET_malloc (sizeof (struct SubsystemEntry) +
+                      slen);
+  memcpy (&se[1],
+          service,
+          slen);
+  se->service = (const char *) &se[1];
+  GNUNET_CONTAINER_DLL_insert (sub_head,
+                               sub_tail,
+                               se);
+  if (NULL != ce)
+    ce->subsystem = se;
+  return se;
+}
+
+
+/**
+ * Find the statistics entry of the given subsystem.
+ *
+ * @param subsystem subsystem to look in
+ * @param name name of the entry to look for
+ * @return statistis entry, or NULL if not found
+ */
+static struct StatsEntry *
+find_stat_entry (struct SubsystemEntry *se,
+                 const char *name)
+{
+  struct StatsEntry *pos;
+
+  for (pos = se->stat_head; NULL != pos; pos = pos->next)
+    if  (0 == strcmp (name, pos->name))
+      return pos;
+  return NULL;
 }
 
 
@@ -316,120 +699,330 @@ handle_set (void *cls,
             struct GNUNET_SERVER_Client *client,
             const struct GNUNET_MessageHeader *message)
 {
-  char *service;
-  char *name;
+  const char *service;
+  const char *name;
+  size_t nlen;
   uint16_t msize;
   uint16_t size;
   const struct GNUNET_STATISTICS_SetMessage *msg;
+  struct SubsystemEntry *se;
+  struct ClientEntry *ce;
   struct StatsEntry *pos;
-  struct StatsEntry *prev;
   uint32_t flags;
   uint64_t value;
   int64_t delta;
+  int changed;
+  int initial_set;
 
+  ce = NULL;
+  if ( (NULL != client) &&
+       (NULL == (ce = make_client_entry (client))) )
+    return; /* new client during shutdown */
   msize = ntohs (message->size);
   if (msize < sizeof (struct GNUNET_STATISTICS_SetMessage))
-    {
-      GNUNET_break (0);
-      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
-      return;
-    }
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
+    return;
+  }
   size = msize - sizeof (struct GNUNET_STATISTICS_SetMessage);
   msg = (const struct GNUNET_STATISTICS_SetMessage *) message;
-
-  if (size != GNUNET_STRINGS_buffer_tokenize ((const char *) &msg[1],
-                                              size, 2, &service, &name))
-    {
-      GNUNET_break (0);
-      GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
-      return;
-    }
-#if DEBUG_STATISTICS
-  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-              "Received request to update statistic on `%s:%s'\n",
-              service, name);
-#endif
+  if (size !=
+      GNUNET_STRINGS_buffer_tokenize ((const char *) &msg[1],
+                                      size,
+                                      2,
+                                      &service,
+                                      &name))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  se = find_subsystem_entry (ce, service);
   flags = ntohl (msg->flags);
   value = GNUNET_ntohll (msg->value);
-  pos = start;
-  prev = NULL;
-  while (pos != NULL)
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Received request to update statistic on `%s:%s' (%u) to/by %llu\n",
+              service,
+              name,
+              (unsigned int) flags,
+              (unsigned long long) value);
+  pos = find_stat_entry (se, name);
+  if (NULL != pos)
+  {
+    initial_set = 0;
+    if (0 == (flags & GNUNET_STATISTICS_SETFLAG_RELATIVE))
     {
-      if (matches (pos, service, name))
-        {
-          if ((flags & GNUNET_STATISTICS_SETFLAG_RELATIVE) == 0)
-            {
-              pos->value = value;
-            }
-          else
-            {
-              delta = (int64_t) value;
-              if ((delta < 0) && (pos->value < -delta))
-                {
-                  pos->value = 0;
-                }
-              else
-                {
-                  GNUNET_break ((delta <= 0) ||
-                                (pos->value + delta > pos->value));
-                  pos->value += delta;
-                }
-            }
-          pos->msg->value = GNUNET_htonll (pos->value);
-          pos->msg->flags = msg->flags;
-          pos->persistent =
-            (0 != (flags & GNUNET_STATISTICS_SETFLAG_PERSISTENT));
-          if (prev != NULL)
-            {
-              /* move to front for faster setting next time! */
-              prev->next = pos->next;
-              pos->next = start;
-              start = pos;
-            }
-#if DEBUG_STATISTICS
-          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-                      "Statistic `%s:%s' updated to value %llu.\n",
-                      service, name, pos->value);
-#endif
-          GNUNET_SERVER_receive_done (client, GNUNET_OK);
-          return;
-        }
-      prev = pos;
-      pos = pos->next;
+      changed = (pos->value != value);
+      pos->value = value;
+    }
+    else
+    {
+      delta = (int64_t) value;
+      if ((delta < 0) && (pos->value < -delta))
+      {
+        changed = (0 != pos->value);
+        pos->value = 0;
+      }
+      else
+      {
+        changed = (0 != delta);
+        GNUNET_break ( (delta <= 0) ||
+                       (pos->value + delta > pos->value) );
+        pos->value += delta;
+      }
+    }
+    if (GNUNET_NO == pos->set)
+    {
+      pos->set = GNUNET_YES;
+      initial_set = 1;
+    }
+    pos->persistent = (0 != (flags & GNUNET_STATISTICS_SETFLAG_PERSISTENT));
+    if (pos != se->stat_head)
+    {
+      /* move to front for faster setting next time! */
+      GNUNET_CONTAINER_DLL_remove (se->stat_head,
+                                   se->stat_tail,
+                                   pos);
+      GNUNET_CONTAINER_DLL_insert (se->stat_head,
+                                   se->stat_tail,
+                                   pos);
     }
-  pos = GNUNET_malloc (sizeof (struct StatsEntry) + msize);
-  pos->next = start;
-  if (((flags & GNUNET_STATISTICS_SETFLAG_RELATIVE) == 0) ||
-      (0 < (int64_t) GNUNET_ntohll (msg->value)))
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Statistic `%s:%s' updated to value %llu (%d).\n",
+                service,
+                name,
+                (unsigned long long) pos->value,
+                pos->persistent);
+    if ( (changed) ||
+         (1 == initial_set) )
+      notify_change (pos);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_OK);
+    return;
+  }
+  /* not found, create a new entry */
+  nlen = strlen (name) + 1;
+  pos = GNUNET_malloc (sizeof (struct StatsEntry) + nlen);
+  memcpy (&pos[1],
+          name,
+          nlen);
+  pos->name = (const char *) &pos[1];
+  pos->subsystem = se;
+  if ( (0 == (flags & GNUNET_STATISTICS_SETFLAG_RELATIVE)) ||
+       (0 < (int64_t) GNUNET_ntohll (msg->value)) )
+  {
     pos->value = GNUNET_ntohll (msg->value);
+    pos->set = GNUNET_YES;
+  }
+  else
+  {
+    pos->set = GNUNET_NO;
+  }
   pos->uid = uidgen++;
   pos->persistent = (0 != (flags & GNUNET_STATISTICS_SETFLAG_PERSISTENT));
-  pos->msg = (void *) &pos[1];
-  memcpy (pos->msg, message, ntohs (message->size));
-  pos->service = (const char *) &pos->msg[1];
-  pos->name = &pos->service[strlen (pos->service) + 1];
-
-  start = pos;
-#if DEBUG_STATISTICS
+  GNUNET_CONTAINER_DLL_insert (se->stat_head,
+                               se->stat_tail,
+                               pos);
   GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
               "New statistic on `%s:%s' with value %llu created.\n",
-              service, name, pos->value);
-#endif
+              service,
+              name,
+              (unsigned long long) pos->value);
+  GNUNET_SERVER_receive_done (client,
+                              GNUNET_OK);
+}
+
+
+/**
+ * Handle WATCH-message.
+ *
+ * @param cls closure
+ * @param client identification of the client
+ * @param message the actual message
+ */
+static void
+handle_watch (void *cls,
+              struct GNUNET_SERVER_Client *client,
+              const struct GNUNET_MessageHeader *message)
+{
+  const char *service;
+  const char *name;
+  uint16_t msize;
+  uint16_t size;
+  struct SubsystemEntry *se;
+  struct StatsEntry *pos;
+  struct ClientEntry *ce;
+  struct WatchEntry *we;
+  size_t nlen;
+
+  if (NULL == nc)
+  {
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  GNUNET_SERVER_client_mark_monitor (client);
+  ce = make_client_entry (client);
+  msize = ntohs (message->size);
+  if (msize < sizeof (struct GNUNET_MessageHeader))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
+    return;
+  }
+  size = msize - sizeof (struct GNUNET_MessageHeader);
+  if (size !=
+      GNUNET_STRINGS_buffer_tokenize ((const char *) &message[1],
+                                      size,
+                                      2,
+                                      &service,
+                                      &name))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client, GNUNET_SYSERR);
+    return;
+  }
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Received request to watch statistic on `%s:%s'\n",
+              service,
+              name);
+  se = find_subsystem_entry (ce, service);
+  pos = find_stat_entry (se, name);
+  if (NULL == pos)
+  {
+    nlen = strlen (name) + 1;
+    pos = GNUNET_malloc (sizeof (struct StatsEntry) +
+                         nlen);
+    memcpy (&pos[1], name, nlen);
+    pos->name = (const char *) &pos[1];
+    pos->subsystem = se;
+    GNUNET_CONTAINER_DLL_insert (se->stat_head,
+                                 se->stat_tail,
+                                 pos);
+    pos->uid = uidgen++;
+    pos->set = GNUNET_NO;
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "New statistic on `%s:%s' with value %llu created.\n",
+                service,
+                name,
+                (unsigned long long) pos->value);
+  }
+  we = GNUNET_new (struct WatchEntry);
+  we->client = client;
+  we->last_value_set = GNUNET_NO;
+  we->wid = ce->max_wid++;
+  GNUNET_CONTAINER_DLL_insert (pos->we_head,
+                               pos->we_tail,
+                               we);
+  if (0 != pos->value)
+    notify_change (pos);
   GNUNET_SERVER_receive_done (client, GNUNET_OK);
 }
 
 
+/**
+ * Actually perform the shutdown.
+ */
+static void
+do_shutdown ()
+{
+  struct WatchEntry *we;
+  struct StatsEntry *pos;
+  struct SubsystemEntry *se;
+
+  if (NULL == nc)
+    return;
+  save ();
+  GNUNET_SERVER_notification_context_destroy (nc);
+  nc = NULL;
+  GNUNET_assert (0 == client_count);
+  while (NULL != (se = sub_head))
+  {
+    GNUNET_CONTAINER_DLL_remove (sub_head,
+                                 sub_tail,
+                                 se);
+    while (NULL != (pos = se->stat_head))
+    {
+      GNUNET_CONTAINER_DLL_remove (se->stat_head,
+                                   se->stat_tail,
+                                   pos);
+      while (NULL != (we = pos->we_head))
+      {
+        GNUNET_break (0);
+        GNUNET_CONTAINER_DLL_remove (pos->we_head,
+                                     pos->we_tail,
+                                     we);
+        GNUNET_free (we);
+      }
+      GNUNET_free (pos);
+    }
+    GNUNET_free (se);
+  }
+}
+
+
 /**
  * Task run during shutdown.
  *
  * @param cls unused
- * @param tc unused
  */
 static void
-shutdown_task (void *cls,
-              const struct GNUNET_SCHEDULER_TaskContext *tc)
+shutdown_task (void *cls)
 {
-  save ();
+  in_shutdown = GNUNET_YES;
+  if (0 != client_count)
+    return;
+  do_shutdown ();
+}
+
+
+/**
+ * A client disconnected.  Remove all of its data structure entries.
+ *
+ * @param cls closure, NULL
+ * @param client identification of the client
+ */
+static void
+handle_client_disconnect (void *cls,
+                          struct GNUNET_SERVER_Client *client)
+{
+  struct ClientEntry *ce;
+  struct WatchEntry *we;
+  struct WatchEntry *wen;
+  struct StatsEntry *pos;
+  struct SubsystemEntry *se;
+
+  if (NULL == client)
+    return;
+  ce = GNUNET_SERVER_client_get_user_context (client,
+                                              struct ClientEntry);
+  if (NULL == ce)
+    return;
+  GNUNET_SERVER_client_set_user_context (client,
+                                         NULL);
+  client_count--;
+  for (se = sub_head; NULL != se; se = se->next)
+  {
+    for (pos = se->stat_head; NULL != pos; pos = pos->next)
+    {
+      wen = pos->we_head;
+      while (NULL != (we = wen))
+      {
+        wen = we->next;
+        if (we->client != client)
+          continue;
+        GNUNET_CONTAINER_DLL_remove (pos->we_head,
+                                     pos->we_tail,
+                                     we);
+        GNUNET_free (we);
+      }
+    }
+  }
+  if ( (0 == client_count) &&
+       (GNUNET_YES == in_shutdown) )
+    do_shutdown ();
 }
 
 
@@ -437,28 +1030,31 @@ shutdown_task (void *cls,
  * Process statistics requests.
  *
  * @param cls closure
- * @param sched scheduler to use
  * @param server the initialized server
  * @param c configuration to use
  */
 static void
 run (void *cls,
-     struct GNUNET_SCHEDULER_Handle *sched,
      struct GNUNET_SERVER_Handle *server,
      const struct GNUNET_CONFIGURATION_Handle *c)
 {
   static const struct GNUNET_SERVER_MessageHandler handlers[] = {
     {&handle_set, NULL, GNUNET_MESSAGE_TYPE_STATISTICS_SET, 0},
     {&handle_get, NULL, GNUNET_MESSAGE_TYPE_STATISTICS_GET, 0},
+    {&handle_watch, NULL, GNUNET_MESSAGE_TYPE_STATISTICS_WATCH, 0},
     {NULL, NULL, 0, 0}
   };
   cfg = c;
-  GNUNET_SERVER_add_handlers (server, handlers);
+  srv = server;
+  GNUNET_SERVER_add_handlers (server,
+                              handlers);
+  nc = GNUNET_SERVER_notification_context_create (server, 16);
+  GNUNET_SERVER_disconnect_notify (server,
+                                   &handle_client_disconnect,
+                                   NULL);
   load (server);
-  GNUNET_SCHEDULER_add_delayed (sched,
-                               GNUNET_TIME_UNIT_FOREVER_REL,
-                               &shutdown_task,
-                               NULL);
+  GNUNET_SCHEDULER_add_shutdown (&shutdown_task,
+                                NULL);
 }
 
 
@@ -473,11 +1069,25 @@ int
 main (int argc, char *const *argv)
 {
   return (GNUNET_OK ==
-          GNUNET_SERVICE_run (argc,
-                              argv,
-                              "statistics",
-                             GNUNET_SERVICE_OPTION_NONE,
-                             &run, NULL)) ? 0 : 1;
+          GNUNET_SERVICE_run (argc, argv, "statistics",
+                              GNUNET_SERVICE_OPTION_SOFT_SHUTDOWN,
+                              &run, NULL)) ? 0 : 1;
 }
 
+#if defined(LINUX) && defined(__GLIBC__)
+#include <malloc.h>
+
+/**
+ * MINIMIZE heap size (way below 128k) since this process doesn't need much.
+ */
+void __attribute__ ((constructor))
+GNUNET_STATISTICS_memory_init ()
+{
+  mallopt (M_TRIM_THRESHOLD, 4 * 1024);
+  mallopt (M_TOP_PAD, 1 * 1024);
+  malloc_trim (0);
+}
+#endif
+
+
 /* end of gnunet-service-statistics.c */