Nearly finished. Call to set_wakeup missing in case of tasks added to pending_timeout
[oweals/gnunet.git] / src / util / scheduler.c
index ba6a04e4f3f3a7debb43fbf43bf164f85cad0176..9061200bd0866919f53eeb8c8b029b9c1655b92a 100644 (file)
@@ -1,6 +1,6 @@
 /*
       This file is part of GNUnet
-      (C) 2009-2013 Christian Grothoff (and other contributing authors)
+      Copyright (C) 2009-2017 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
 
       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 util/scheduler.c
  * @brief schedule computations using continuation passing style
 
 
 /**
- * Linked list of pending tasks.
+ * Argument to be passed from the driver to
+ * #GNUNET_SCHEDULER_run_from_driver().  Contains the
+ * scheduler's internal state.
+ */
+struct GNUNET_SCHEDULER_Handle
+{
+  /**
+   * Passed here to avoid constantly allocating/deallocating
+   * this element, but generally we want to get rid of this.
+   * @deprecated
+   */
+  struct GNUNET_NETWORK_FDSet *rs;
+
+  /**
+   * Passed here to avoid constantly allocating/deallocating
+   * this element, but generally we want to get rid of this.
+   * @deprecated
+   */
+  struct GNUNET_NETWORK_FDSet *ws;
+
+  /**
+   * Driver we used for the event loop.
+   */
+  const struct GNUNET_SCHEDULER_Driver *driver;
+
+};
+
+
+/**
+ * Entry in list of pending tasks.
  */
-struct Task
+struct GNUNET_SCHEDULER_Task
 {
   /**
    * This is a linked list.
    */
-  struct Task *next;
+  struct GNUNET_SCHEDULER_Task *next;
+
+  /**
+   * This is a linked list.
+   */
+  struct GNUNET_SCHEDULER_Task *prev;
 
   /**
    * Function to run when ready.
    */
-  GNUNET_SCHEDULER_Task callback;
+  GNUNET_SCHEDULER_TaskCallback callback;
 
   /**
    * Closure for the @e callback.
    */
   void *callback_cls;
 
+  /**
+   * Handle to the scheduler's state.
+   */
+  const struct GNUNET_SCHEDULER_Handle *sh;
+
   /**
    * Set of file descriptors this task is waiting
    * for for reading.  Once ready, this is updated
@@ -106,13 +144,20 @@ struct Task
   struct GNUNET_NETWORK_FDSet *write_set;
 
   /**
-   * Unique task identifier.
+   * Information about which FDs are ready for this task (and why).
+   */
+  const struct GNUNET_SCHEDULER_FdInfo *fds;
+
+  /**
+   * Storage location used for @e fds if we want to avoid
+   * a separate malloc() call in the common case that this
+   * task is only about a single FD.
    */
-  GNUNET_SCHEDULER_TaskIdentifier id;
+  struct GNUNET_SCHEDULER_FdInfo fdx;
 
   /**
    * Absolute timeout value for the task, or
-   * GNUNET_TIME_UNIT_FOREVER_ABS for "no timeout".
+   * #GNUNET_TIME_UNIT_FOREVER_ABS for "no timeout".
    */
   struct GNUNET_TIME_Absolute timeout;
 
@@ -123,6 +168,11 @@ struct Task
   struct GNUNET_TIME_Absolute start_time;
 #endif
 
+  /**
+   * Size of the @e fds array.
+   */
+  unsigned int fds_len;
+
   /**
    * Why is the task ready?  Set after task is added to ready queue.
    * Initially set to zero.  All reasons that have already been
@@ -151,6 +201,16 @@ struct Task
    */
   int lifeness;
 
+  /**
+   * Is this task run on shutdown?
+   */
+  int on_shutdown;
+
+  /**
+   * Is this task in the ready list?
+   */
+  int in_ready_list;
+
 #if EXECINFO
   /**
    * Array of strings which make up a backtrace from the point when this
@@ -167,11 +227,43 @@ struct Task
 
 };
 
+/**
+ * The driver used for the event loop. Will be handed over to
+ * the scheduler in #GNUNET_SCHEDULER_run_from_driver(), peristed
+ * there in this variable for later use in functions like
+ * #GNUNET_SCHEDULER_add_select(), #add_without_sets() and
+ * #GNUNET_SCHEDULER_cancel().
+ */
+static const struct GNUNET_SCHEDULER_Driver *scheduler_driver;
+
+/**
+ * Head of list of tasks waiting for an event.
+ */
+static struct GNUNET_SCHEDULER_Task *pending_head;
+
+/**
+ * Tail of list of tasks waiting for an event.
+ */
+static struct GNUNET_SCHEDULER_Task *pending_tail;
+
+/**
+ * Head of list of tasks waiting for shutdown.
+ */
+static struct GNUNET_SCHEDULER_Task *shutdown_head;
+
+/**
+ * Tail of list of tasks waiting for shutdown.
+ */
+static struct GNUNET_SCHEDULER_Task *shutdown_tail;
 
 /**
- * List of tasks waiting for an event.
+ * List of tasks waiting ONLY for a timeout event.
+ * Sorted by timeout (earliest first).  Used so that
+ * we do not traverse the list of these tasks when
+ * building select sets (we just look at the head
+ * to determine the respective timeout ONCE).
  */
-static struct Task *pending;
+static struct GNUNET_SCHEDULER_Task *pending_timeout_head;
 
 /**
  * List of tasks waiting ONLY for a timeout event.
@@ -180,31 +272,28 @@ static struct Task *pending;
  * building select sets (we just look at the head
  * to determine the respective timeout ONCE).
  */
-static struct Task *pending_timeout;
+static struct GNUNET_SCHEDULER_Task *pending_timeout_tail;
 
 /**
  * Last inserted task waiting ONLY for a timeout event.
  * Used to (heuristically) speed up insertion.
  */
-static struct Task *pending_timeout_last;
+static struct GNUNET_SCHEDULER_Task *pending_timeout_last;
 
 /**
  * ID of the task that is running right now.
  */
-static struct Task *active_task;
+static struct GNUNET_SCHEDULER_Task *active_task;
 
 /**
- * List of tasks ready to run right now,
- * grouped by importance.
+ * Head of list of tasks ready to run right now, grouped by importance.
  */
-static struct Task *ready[GNUNET_SCHEDULER_PRIORITY_COUNT];
+static struct GNUNET_SCHEDULER_Task *ready_head[GNUNET_SCHEDULER_PRIORITY_COUNT];
 
 /**
- * Identity of the last task queued.  Incremented for each task to
- * generate a unique task ID (it is virtually impossible to start
- * more than 2^64 tasks during the lifetime of a process).
+ * Tail of list of tasks ready to run right now, grouped by importance.
  */
-static GNUNET_SCHEDULER_TaskIdentifier last_id;
+static struct GNUNET_SCHEDULER_Task *ready_tail[GNUNET_SCHEDULER_PRIORITY_COUNT];
 
 /**
  * Number of tasks on the ready list.
@@ -240,10 +329,16 @@ static int current_lifeness;
 static GNUNET_SCHEDULER_select scheduler_select;
 
 /**
- * Closure for 'scheduler_select'.
+ * Task context of the current task.
+ */
+static struct GNUNET_SCHEDULER_TaskContext tc;
+
+/**
+ * Closure for #scheduler_select.
  */
 static void *scheduler_select_cls;
 
+
 /**
  * Sets the select function to use in the scheduler (scheduler_select).
  *
@@ -283,26 +378,38 @@ check_priority (enum GNUNET_SCHEDULER_Priority p)
  * @param ws write-set, set to all FDs we would like to write (updated)
  * @param timeout next timeout (updated)
  */
-static void
-update_sets (struct GNUNET_NETWORK_FDSet *rs, struct GNUNET_NETWORK_FDSet *ws,
-             struct GNUNET_TIME_Relative *timeout)
+void getNextPendingTimeout(struct GNUNET_TIME_Relative *timeout)
 {
-  struct Task *pos;
+
+  struct GNUNET_SCHEDULER_Task *pos;
   struct GNUNET_TIME_Absolute now;
   struct GNUNET_TIME_Relative to;
 
   now = GNUNET_TIME_absolute_get ();
-  pos = pending_timeout;
+  pos = pending_timeout_head;
   if (NULL != pos)
   {
     to = GNUNET_TIME_absolute_get_difference (now, pos->timeout);
     if (timeout->rel_value_us > to.rel_value_us)
       *timeout = to;
-    if (pos->reason != 0)
+    if (0 != pos->reason)
       *timeout = GNUNET_TIME_UNIT_ZERO;
   }
-  pos = pending;
-  while (NULL != pos)
+}
+
+static void
+update_sets (struct GNUNET_NETWORK_FDSet *rs,
+             struct GNUNET_NETWORK_FDSet *ws,
+             struct GNUNET_TIME_Relative *timeout)
+{
+  struct GNUNET_SCHEDULER_Task *pos;
+  struct GNUNET_TIME_Absolute now;
+  struct GNUNET_TIME_Relative to;
+
+  now = GNUNET_TIME_absolute_get ();
+
+  getNextPendingTimeout(timeout);
+  for (pos = pending_head; NULL != pos; pos = pos->next)
   {
     if (pos->timeout.abs_value_us != GNUNET_TIME_UNIT_FOREVER_ABS.abs_value_us)
     {
@@ -320,7 +427,6 @@ update_sets (struct GNUNET_NETWORK_FDSet *rs, struct GNUNET_NETWORK_FDSet *ws,
       GNUNET_NETWORK_fdset_add (ws, pos->write_set);
     if (0 != pos->reason)
       *timeout = GNUNET_TIME_UNIT_ZERO;
-    pos = pos->next;
   }
 }
 
@@ -328,11 +434,11 @@ update_sets (struct GNUNET_NETWORK_FDSet *rs, struct GNUNET_NETWORK_FDSet *ws,
 /**
  * Check if the ready set overlaps with the set we want to have ready.
  * If so, update the want set (set all FDs that are ready).  If not,
- * return GNUNET_NO.
+ * return #GNUNET_NO.
  *
  * @param ready set that is ready
  * @param want set that we want to be ready
- * @return GNUNET_YES if there was some overlap
+ * @return #GNUNET_YES if there was some overlap
  */
 static int
 set_overlaps (const struct GNUNET_NETWORK_FDSet *ready,
@@ -362,7 +468,8 @@ set_overlaps (const struct GNUNET_NETWORK_FDSet *ready,
  * @return #GNUNET_YES if we can run it, #GNUNET_NO if not.
  */
 static int
-is_ready (struct Task *task, struct GNUNET_TIME_Absolute now,
+is_ready (struct GNUNET_SCHEDULER_Task *task,
+          struct GNUNET_TIME_Absolute now,
           const struct GNUNET_NETWORK_FDSet *rs,
           const struct GNUNET_NETWORK_FDSet *ws)
 {
@@ -395,14 +502,14 @@ is_ready (struct Task *task, struct GNUNET_TIME_Absolute now,
  * @param task task ready for execution
  */
 static void
-queue_ready_task (struct Task *task)
+queue_ready_task (struct GNUNET_SCHEDULER_Task *task)
 {
-  enum GNUNET_SCHEDULER_Priority p = task->priority;
+  enum GNUNET_SCHEDULER_Priority p = check_priority (task->priority);
 
-  if (0 != (task->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
-    p = GNUNET_SCHEDULER_PRIORITY_SHUTDOWN;
-  task->next = ready[check_priority (p)];
-  ready[check_priority (p)] = task;
+  GNUNET_CONTAINER_DLL_insert (ready_head[p],
+                               ready_tail[p],
+                               task);
+  task->in_ready_list = GNUNET_YES;
   ready_count++;
 }
 
@@ -418,92 +525,58 @@ static void
 check_ready (const struct GNUNET_NETWORK_FDSet *rs,
              const struct GNUNET_NETWORK_FDSet *ws)
 {
-  struct Task *pos;
-  struct Task *prev;
-  struct Task *next;
+  struct GNUNET_SCHEDULER_Task *pos;
+  struct GNUNET_SCHEDULER_Task *next;
   struct GNUNET_TIME_Absolute now;
 
   now = GNUNET_TIME_absolute_get ();
-  prev = NULL;
-  pos = pending_timeout;
-  while (NULL != pos)
+  while (NULL != (pos = pending_timeout_head))
   {
-    next = pos->next;
     if (now.abs_value_us >= pos->timeout.abs_value_us)
       pos->reason |= GNUNET_SCHEDULER_REASON_TIMEOUT;
     if (0 == pos->reason)
       break;
-    pending_timeout = next;
+    GNUNET_CONTAINER_DLL_remove (pending_timeout_head,
+                                 pending_timeout_tail,
+                                 pos);
     if (pending_timeout_last == pos)
       pending_timeout_last = NULL;
     queue_ready_task (pos);
-    pos = next;
   }
-  pos = pending;
+  pos = pending_head;
   while (NULL != pos)
   {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-        "Checking readiness of task: %llu / %p\n",
-         pos->id, pos->callback_cls);
     next = pos->next;
     if (GNUNET_YES == is_ready (pos, now, rs, ws))
     {
-      if (NULL == prev)
-        pending = next;
-      else
-        prev->next = next;
+      GNUNET_CONTAINER_DLL_remove (pending_head,
+                                   pending_tail,
+                                   pos);
       queue_ready_task (pos);
-      pos = next;
-      continue;
     }
-    prev = pos;
     pos = next;
   }
 }
 
 
 /**
- * Request the shutdown of a scheduler.  Marks all currently
- * pending tasks as ready because of shutdown.  This will
- * cause all tasks to run (as soon as possible, respecting
- * priorities and prerequisite tasks).  Note that tasks
- * scheduled AFTER this call may still be delayed arbitrarily.
+ * Request the shutdown of a scheduler.  Marks all tasks
+ * awaiting shutdown as ready. Note that tasks
+ * scheduled with #GNUNET_SCHEDULER_add_shutdown() AFTER this call
+ * will be delayed until the next shutdown signal.
  */
 void
 GNUNET_SCHEDULER_shutdown ()
 {
-  struct Task *pos;
-  int i;
+  struct GNUNET_SCHEDULER_Task *pos;
 
-  pos = pending_timeout;
-  while (NULL != pos)
-  {
-    pos->reason |= GNUNET_SCHEDULER_REASON_SHUTDOWN;
-    /* we don't move the task into the ready queue yet; check_ready
-     * will do that later, possibly adding additional
-     * readiness-factors */
-    pos = pos->next;
-  }
-  pos = pending;
-  while (NULL != pos)
+  while (NULL != (pos = shutdown_head))
   {
+    GNUNET_CONTAINER_DLL_remove (shutdown_head,
+                                 shutdown_tail,
+                                 pos);
     pos->reason |= GNUNET_SCHEDULER_REASON_SHUTDOWN;
-    /* we don't move the task into the ready queue yet; check_ready
-     * will do that later, possibly adding additional
-     * readiness-factors */
-    pos = pos->next;
-  }
-  for (i = 0; i < GNUNET_SCHEDULER_PRIORITY_COUNT; i++)
-  {
-    pos = ready[i];
-    while (NULL != pos)
-    {
-      pos->reason |= GNUNET_SCHEDULER_REASON_SHUTDOWN;
-      /* we don't move the task into the ready queue yet; check_ready
-       * will do that later, possibly adding additional
-       * readiness-factors */
-      pos = pos->next;
-    }
+    queue_ready_task (pos);
   }
 }
 
@@ -514,7 +587,7 @@ GNUNET_SCHEDULER_shutdown ()
  * @param t task to destroy
  */
 static void
-destroy_task (struct Task *t)
+destroy_task (struct GNUNET_SCHEDULER_Task *t)
 {
   if (NULL != t->read_set)
     GNUNET_NETWORK_fdset_destroy (t->read_set);
@@ -527,6 +600,27 @@ destroy_task (struct Task *t)
 }
 
 
+/**
+ * Output stack trace of task @a t.
+ *
+ * @param t task to dump stack trace of
+ */
+static void
+dump_backtrace (struct GNUNET_SCHEDULER_Task *t)
+{
+#if EXECINFO
+  unsigned int i;
+
+  for (i = 0; i < t->num_backtrace_strings; i++)
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+   "Task %p trace %u: %s\n",
+   t,
+   i,
+   t->backtrace_strings[i]);
+#endif
+}
+
+
 /**
  * Run at least one task in the highest-priority queue that is not
  * empty.  Keep running tasks until we are either no longer running
@@ -542,25 +636,26 @@ run_ready (struct GNUNET_NETWORK_FDSet *rs,
            struct GNUNET_NETWORK_FDSet *ws)
 {
   enum GNUNET_SCHEDULER_Priority p;
-  struct Task *pos;
-  struct GNUNET_SCHEDULER_TaskContext tc;
+  struct GNUNET_SCHEDULER_Task *pos;
 
   max_priority_added = GNUNET_SCHEDULER_PRIORITY_KEEP;
   do
   {
     if (0 == ready_count)
       return;
-    GNUNET_assert (ready[GNUNET_SCHEDULER_PRIORITY_KEEP] == NULL);
+    GNUNET_assert (NULL == ready_head[GNUNET_SCHEDULER_PRIORITY_KEEP]);
     /* yes, p>0 is correct, 0 is "KEEP" which should
      * always be an empty queue (see assertion)! */
     for (p = GNUNET_SCHEDULER_PRIORITY_COUNT - 1; p > 0; p--)
     {
-      pos = ready[p];
+      pos = ready_head[p];
       if (NULL != pos)
         break;
     }
     GNUNET_assert (NULL != pos);        /* ready_count wrong? */
-    ready[p] = pos->next;
+    GNUNET_CONTAINER_DLL_remove (ready_head[p],
+                                 ready_tail[p],
+                                 pos);
     ready_count--;
     current_priority = pos->priority;
     current_lifeness = pos->lifeness;
@@ -570,46 +665,38 @@ run_ready (struct GNUNET_NETWORK_FDSet *rs,
         DELAY_THRESHOLD.rel_value_us)
     {
       LOG (GNUNET_ERROR_TYPE_DEBUG,
-          "Task %llu took %s to be scheduled\n",
-           (unsigned long long) pos->id,
+     "Task %p took %s to be scheduled\n",
+           pos,
            GNUNET_STRINGS_relative_time_to_string (GNUNET_TIME_absolute_get_duration (pos->start_time),
                                                    GNUNET_YES));
     }
 #endif
     tc.reason = pos->reason;
-    tc.read_ready = (pos->read_set == NULL) ? rs : pos->read_set;
-    if ((pos->read_fd != -1) &&
+    tc.read_ready = (NULL == pos->read_set) ? rs : pos->read_set;
+    if ((-1 != pos->read_fd) &&
         (0 != (pos->reason & GNUNET_SCHEDULER_REASON_READ_READY)))
       GNUNET_NETWORK_fdset_set_native (rs, pos->read_fd);
-    tc.write_ready = (pos->write_set == NULL) ? ws : pos->write_set;
-    if ((pos->write_fd != -1) &&
+    tc.write_ready = (NULL == pos->write_set) ? ws : pos->write_set;
+    if ((-1 != pos->write_fd) &&
         (0 != (pos->reason & GNUNET_SCHEDULER_REASON_WRITE_READY)))
       GNUNET_NETWORK_fdset_set_native (ws, pos->write_fd);
-    if (((tc.reason & GNUNET_SCHEDULER_REASON_WRITE_READY) != 0) &&
-        (pos->write_fd != -1) &&
+    if ((0 != (tc.reason & GNUNET_SCHEDULER_REASON_WRITE_READY)) &&
+        (-1 != pos->write_fd) &&
         (!GNUNET_NETWORK_fdset_test_native (ws, pos->write_fd)))
-      GNUNET_abort ();          // added to ready in previous select loop!
+      GNUNET_assert (0);          // added to ready in previous select loop!
     LOG (GNUNET_ERROR_TYPE_DEBUG,
-        "Running task: %llu / %p\n", pos->id,
-         pos->callback_cls);
-    pos->callback (pos->callback_cls, &tc);
-#if EXECINFO
-    int i;
-
-    for (i = 0; i < pos->num_backtrace_strings; i++)
-      LOG (GNUNET_ERROR_TYPE_ERROR,
-           "Task %llu trace %d: %s\n",
-           pos->id,
-           i,
-           pos->backtrace_strings[i]);
-#endif
+   "Running task: %p\n",
+         pos);
+    pos->callback (pos->callback_cls);
+    dump_backtrace (pos);
     active_task = NULL;
     destroy_task (pos);
     tasks_run++;
   }
-  while ((NULL == pending) || (p >= max_priority_added));
+  while ((NULL == pending_head) || (p >= max_priority_added));
 }
 
+
 /**
  * Pipe used to communicate shutdown via signal.
  */
@@ -671,7 +758,7 @@ sighandler_shutdown ()
 
 
 /**
- * Check if the system is still life. Trigger shutdown if we
+ * Check if the system is still alive. Trigger shutdown if we
  * have tasks, but none of them give us lifeness.
  *
  * @return #GNUNET_OK to continue the main loop,
@@ -680,17 +767,20 @@ sighandler_shutdown ()
 static int
 check_lifeness ()
 {
-  struct Task *t;
+  struct GNUNET_SCHEDULER_Task *t;
 
   if (ready_count > 0)
     return GNUNET_OK;
-  for (t = pending; NULL != t; t = t->next)
+  for (t = pending_head; NULL != t; t = t->next)
+    if (t->lifeness == GNUNET_YES)
+      return GNUNET_OK;
+  for (t = shutdown_head; NULL != t; t = t->next)
     if (t->lifeness == GNUNET_YES)
       return GNUNET_OK;
-  for (t = pending_timeout; NULL != t; t = t->next)
+  for (t = pending_timeout_head; NULL != t; t = t->next)
     if (t->lifeness == GNUNET_YES)
       return GNUNET_OK;
-  if ((NULL != pending) || (NULL != pending_timeout))
+  if (NULL != shutdown_head)
   {
     GNUNET_SCHEDULER_shutdown ();
     return GNUNET_OK;
@@ -699,75 +789,22 @@ check_lifeness ()
 }
 
 
-/**
- * Initialize and run scheduler.  This function will return when all
- * tasks have completed.  On systems with signals, receiving a SIGTERM
- * (and other similar signals) will cause #GNUNET_SCHEDULER_shutdown()
- * to be run after the active task is complete.  As a result, SIGTERM
- * causes all active tasks to be scheduled with reason
- * #GNUNET_SCHEDULER_REASON_SHUTDOWN.  (However, tasks added
- * afterwards will execute normally!). Note that any particular signal
- * will only shut down one scheduler; applications should always only
- * create a single scheduler.
- *
- * @param task task to run immediately
- * @param task_cls closure of @a task
- */
-void
-GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_Task task, void *task_cls)
+
+void while_live(struct GNUNET_NETWORK_FDSet *rs, struct GNUNET_NETWORK_FDSet *ws)
 {
-  struct GNUNET_NETWORK_FDSet *rs;
-  struct GNUNET_NETWORK_FDSet *ws;
-  struct GNUNET_TIME_Relative timeout;
   int ret;
-  struct GNUNET_SIGNAL_Context *shc_int;
-  struct GNUNET_SIGNAL_Context *shc_term;
-#if (SIGTERM != GNUNET_TERM_SIG)
-  struct GNUNET_SIGNAL_Context *shc_gterm;
-#endif
-
-#ifndef MINGW
-  struct GNUNET_SIGNAL_Context *shc_quit;
-  struct GNUNET_SIGNAL_Context *shc_hup;
-  struct GNUNET_SIGNAL_Context *shc_pipe;
-#endif
-  unsigned long long last_tr;
   unsigned int busy_wait_warning;
+  unsigned long long last_tr;
   const struct GNUNET_DISK_FileHandle *pr;
   char c;
+  struct GNUNET_TIME_Relative timeout;
 
-  GNUNET_assert (NULL == active_task);
-  rs = GNUNET_NETWORK_fdset_create ();
-  ws = GNUNET_NETWORK_fdset_create ();
-  GNUNET_assert (NULL == shutdown_pipe_handle);
-  shutdown_pipe_handle = GNUNET_DISK_pipe (GNUNET_NO, GNUNET_NO, GNUNET_NO, GNUNET_NO);
-  GNUNET_assert (NULL != shutdown_pipe_handle);
+  busy_wait_warning = 0;
   pr = GNUNET_DISK_pipe_handle (shutdown_pipe_handle,
                                 GNUNET_DISK_PIPE_END_READ);
-  GNUNET_assert (pr != NULL);
-  my_pid = getpid ();
-  LOG (GNUNET_ERROR_TYPE_DEBUG, "Registering signal handlers\n");
-  shc_int = GNUNET_SIGNAL_handler_install (SIGINT, &sighandler_shutdown);
-  shc_term = GNUNET_SIGNAL_handler_install (SIGTERM, &sighandler_shutdown);
-#if (SIGTERM != GNUNET_TERM_SIG)
-  shc_gterm = GNUNET_SIGNAL_handler_install (GNUNET_TERM_SIG, &sighandler_shutdown);
-#endif
-#ifndef MINGW
-  shc_pipe = GNUNET_SIGNAL_handler_install (SIGPIPE, &sighandler_pipe);
-  shc_quit = GNUNET_SIGNAL_handler_install (SIGQUIT, &sighandler_shutdown);
-  shc_hup = GNUNET_SIGNAL_handler_install (SIGHUP, &sighandler_shutdown);
-#endif
-  current_priority = GNUNET_SCHEDULER_PRIORITY_DEFAULT;
-  current_lifeness = GNUNET_YES;
-  GNUNET_SCHEDULER_add_continuation (task, task_cls,
-                                     GNUNET_SCHEDULER_REASON_STARTUP);
-  active_task = (void *) (long) -1;     /* force passing of sanity check */
-  GNUNET_SCHEDULER_add_now_with_lifeness (GNUNET_NO,
-                                          &GNUNET_OS_install_parent_control_handler,
-                                          NULL);
-  active_task = NULL;
+  GNUNET_assert (NULL != pr);
   last_tr = 0;
-  busy_wait_warning = 0;
+
   while (GNUNET_OK == check_lifeness ())
   {
     GNUNET_NETWORK_fdset_zero (rs);
@@ -781,9 +818,16 @@ GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_Task task, void *task_cls)
       timeout = GNUNET_TIME_UNIT_ZERO;
     }
     if (NULL == scheduler_select)
-      ret = GNUNET_NETWORK_socket_select (rs, ws, NULL, timeout);
+      ret = GNUNET_NETWORK_socket_select (rs,
+                                          ws,
+                                          NULL,
+                                          timeout);
     else
-      ret = scheduler_select (scheduler_select_cls, rs, ws, NULL, timeout);
+      ret = scheduler_select (scheduler_select_cls,
+                              rs,
+                              ws,
+                              NULL,
+                              timeout);
     if (ret == GNUNET_SYSERR)
     {
       if (errno == EINTR)
@@ -802,15 +846,45 @@ GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_Task task, void *task_cls)
                       "system");
 #endif
 #endif
-      GNUNET_abort ();
+#if DEBUG_FDS
+      struct GNUNET_SCHEDULER_Task *t;
+
+      for (t = pending_head; NULL != t; t = t->next)
+      {
+        if (-1 != t->read_fd)
+        {
+          int flags = fcntl (t->read_fd, F_GETFD);
+          if ((flags == -1) && (errno == EBADF))
+            {
+              LOG (GNUNET_ERROR_TYPE_ERROR,
+                   "Got invalid file descriptor %d!\n",
+                   t->read_fd);
+              dump_backtrace (t);
+            }
+        }
+        if (-1 != t->write_fd)
+          {
+            int flags = fcntl (t->write_fd, F_GETFD);
+            if ((flags == -1) && (errno == EBADF))
+              {
+                LOG (GNUNET_ERROR_TYPE_ERROR,
+                     "Got invalid file descriptor %d!\n",
+                     t->write_fd);
+                dump_backtrace (t);
+              }
+          }
+      }
+#endif
+      GNUNET_assert (0);
       break;
     }
+
     if ( (0 == ret) &&
          (0 == timeout.rel_value_us) &&
          (busy_wait_warning > 16) )
     {
       LOG (GNUNET_ERROR_TYPE_WARNING,
-           _("Looks like we're busy waiting...\n"));
+           "Looks like we're busy waiting...\n");
       short_wait (100);                /* mitigate */
     }
     check_ready (rs, ws);
@@ -833,6 +907,87 @@ GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_Task task, void *task_cls)
       busy_wait_warning = 0;
     }
   }
+}
+
+/**
+ * Initialize and run scheduler.  This function will return when all
+ * tasks have completed.  On systems with signals, receiving a SIGTERM
+ * (and other similar signals) will cause #GNUNET_SCHEDULER_shutdown()
+ * to be run after the active task is complete.  As a result, SIGTERM
+ * causes all active tasks to be scheduled with reason
+ * #GNUNET_SCHEDULER_REASON_SHUTDOWN.  (However, tasks added
+ * afterwards will execute normally!). Note that any particular signal
+ * will only shut down one scheduler; applications should always only
+ * create a single scheduler.
+ *
+ * @param task task to run immediately
+ * @param task_cls closure of @a task
+ */
+void
+GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_TaskCallback task,
+                      void *task_cls)
+{
+  struct GNUNET_NETWORK_FDSet *rs;
+  struct GNUNET_NETWORK_FDSet *ws;
+
+
+  struct GNUNET_SIGNAL_Context *shc_int;
+  struct GNUNET_SIGNAL_Context *shc_term;
+#if (SIGTERM != GNUNET_TERM_SIG)
+  struct GNUNET_SIGNAL_Context *shc_gterm;
+#endif
+
+#ifndef MINGW
+  struct GNUNET_SIGNAL_Context *shc_quit;
+  struct GNUNET_SIGNAL_Context *shc_hup;
+  struct GNUNET_SIGNAL_Context *shc_pipe;
+#endif
+
+
+
+  GNUNET_assert (NULL == active_task);
+  rs = GNUNET_NETWORK_fdset_create ();
+  ws = GNUNET_NETWORK_fdset_create ();
+  GNUNET_assert (NULL == shutdown_pipe_handle);
+  shutdown_pipe_handle = GNUNET_DISK_pipe (GNUNET_NO,
+                                           GNUNET_NO,
+                                           GNUNET_NO,
+                                           GNUNET_NO);
+  GNUNET_assert (NULL != shutdown_pipe_handle);
+
+  my_pid = getpid ();
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Registering signal handlers\n");
+  shc_int = GNUNET_SIGNAL_handler_install (SIGINT,
+             &sighandler_shutdown);
+  shc_term = GNUNET_SIGNAL_handler_install (SIGTERM,
+              &sighandler_shutdown);
+#if (SIGTERM != GNUNET_TERM_SIG)
+  shc_gterm = GNUNET_SIGNAL_handler_install (GNUNET_TERM_SIG,
+               &sighandler_shutdown);
+#endif
+#ifndef MINGW
+  shc_pipe = GNUNET_SIGNAL_handler_install (SIGPIPE,
+              &sighandler_pipe);
+  shc_quit = GNUNET_SIGNAL_handler_install (SIGQUIT,
+              &sighandler_shutdown);
+  shc_hup = GNUNET_SIGNAL_handler_install (SIGHUP,
+             &sighandler_shutdown);
+#endif
+  current_priority = GNUNET_SCHEDULER_PRIORITY_DEFAULT;
+  current_lifeness = GNUNET_YES;
+  GNUNET_SCHEDULER_add_with_reason_and_priority (task,
+                                                 task_cls,
+                                                 GNUNET_SCHEDULER_REASON_STARTUP,
+                                                 GNUNET_SCHEDULER_PRIORITY_DEFAULT);
+  active_task = (void *) (long) -1;     /* force passing of sanity check */
+  GNUNET_SCHEDULER_add_now_with_lifeness (GNUNET_NO,
+                                          &GNUNET_OS_install_parent_control_handler,
+                                          NULL);
+  active_task = NULL;
+
+
+  while_live(rs, ws);
   GNUNET_SIGNAL_handler_uninstall (shc_int);
   GNUNET_SIGNAL_handler_uninstall (shc_term);
 #if (SIGTERM != GNUNET_TERM_SIG)
@@ -851,17 +1006,16 @@ GNUNET_SCHEDULER_run (GNUNET_SCHEDULER_Task task, void *task_cls)
 
 
 /**
- * Obtain the reason code for why the current task was
- * started.  Will return the same value as
- * the `struct GNUNET_SCHEDULER_TaskContext`'s reason field.
+ * Obtain the task context, giving the reason why the current task was
+ * started.
  *
- * @return reason(s) why the current task is run
+ * @return current tasks' scheduler context
  */
-enum GNUNET_SCHEDULER_Reason
-GNUNET_SCHEDULER_get_reason ()
+const struct GNUNET_SCHEDULER_TaskContext *
+GNUNET_SCHEDULER_get_task_context ()
 {
-  GNUNET_assert (active_task != NULL);
-  return active_task->reason;
+  GNUNET_assert (NULL != active_task);
+  return &tc;
 }
 
 
@@ -877,24 +1031,75 @@ GNUNET_SCHEDULER_get_reason ()
 unsigned int
 GNUNET_SCHEDULER_get_load (enum GNUNET_SCHEDULER_Priority p)
 {
-  struct Task *pos;
+  struct GNUNET_SCHEDULER_Task *pos;
   unsigned int ret;
 
-  GNUNET_assert (active_task != NULL);
+  GNUNET_assert (NULL != active_task);
   if (p == GNUNET_SCHEDULER_PRIORITY_COUNT)
     return ready_count;
   if (p == GNUNET_SCHEDULER_PRIORITY_KEEP)
     p = current_priority;
   ret = 0;
-  pos = ready[check_priority (p)];
-  while (NULL != pos)
-  {
-    pos = pos->next;
+  for (pos = ready_head[check_priority (p)]; NULL != pos; pos = pos->next)
     ret++;
-  }
   return ret;
 }
 
+static struct GNUNET_SCHEDULER_Task*
+initFdInfo(const struct GNUNET_NETWORK_Handle *read_nh,
+           const struct GNUNET_NETWORK_Handle *write_nh,
+           const struct GNUNET_DISK_FileHandle *read_fh,
+           const struct GNUNET_DISK_FileHandle *write_fh)
+{
+
+
+  struct GNUNET_SCHEDULER_Task *t;
+
+  t = GNUNET_new (struct GNUNET_SCHEDULER_Task);
+
+  // either only network handles or only file handles are allowed
+  GNUNET_assert (!((NULL != read_nh || NULL != write_nh) && (NULL != read_fh || NULL != write_fh)));
+
+  if (NULL != read_nh && NULL != write_nh)
+  {
+    t->fds_len = 2;
+    t->fds = GNUNET_new_array (2, struct GNUNET_SCHEDULER_FdInfo);
+    const struct GNUNET_SCHEDULER_FdInfo read_fdi = { .fd = read_nh, .et = GNUNET_SCHEDULER_ET_IN, .sock = GNUNET_NETWORK_get_fd (read_nh)};
+    const struct GNUNET_SCHEDULER_FdInfo write_fdi = { .fd = write_nh, .et = GNUNET_SCHEDULER_ET_OUT, .sock = GNUNET_NETWORK_get_fd (write_nh)};
+
+    const struct GNUNET_SCHEDULER_FdInfo array[2] = {read_fdi, write_fdi};
+    t->fds = array;
+  }
+  else if (NULL != read_fh && NULL != write_fh)
+  {
+    t->fds_len = 2;
+    t->fds = GNUNET_new_array (2, struct GNUNET_SCHEDULER_FdInfo);
+    const struct GNUNET_SCHEDULER_FdInfo read_fdi = { .fh = read_fh, .et = GNUNET_SCHEDULER_ET_IN};
+    const struct GNUNET_SCHEDULER_FdInfo write_fdi = { .fh = write_fh, .et = GNUNET_SCHEDULER_ET_OUT, .sock = GNUNET_NETWORK_get_fd (write_nh)};
+    const struct GNUNET_SCHEDULER_FdInfo array[2] = {read_fdi, write_fdi};
+    t->fds = array;
+  }
+  else if (NULL != read_nh)
+  {
+    struct GNUNET_SCHEDULER_FdInfo read_fdi = { .fd = read_nh, .et = GNUNET_SCHEDULER_ET_IN, .sock = GNUNET_NETWORK_get_fd (read_nh)};
+    t->fdx = read_fdi;
+  }
+  else if (NULL != write_nh)
+  {
+    struct GNUNET_SCHEDULER_FdInfo write_fdi = { .fd = write_nh, .et = GNUNET_SCHEDULER_ET_OUT, .sock = GNUNET_NETWORK_get_fd (write_nh)};
+    t->fdx = write_fdi;
+  }
+  else if (NULL != read_fh)
+  {
+    struct GNUNET_SCHEDULER_FdInfo read_fdi = { .fh = read_fh, .et = GNUNET_SCHEDULER_ET_IN};
+    t->fdx = read_fdi;
+  }
+  else if (NULL != write_fh)
+  {
+    struct GNUNET_SCHEDULER_FdInfo write_fdi = { .fh = write_fh, .et = GNUNET_SCHEDULER_ET_OUT, .sock = GNUNET_NETWORK_get_fd (write_nh)};
+    t->fdx = write_fdi;
+  }
+}
 
 /**
  * Cancel the task with the specified identifier.
@@ -904,96 +1109,74 @@ GNUNET_SCHEDULER_get_load (enum GNUNET_SCHEDULER_Priority p)
  * @return original closure of the task
  */
 void *
-GNUNET_SCHEDULER_cancel (GNUNET_SCHEDULER_TaskIdentifier task)
+GNUNET_SCHEDULER_cancel (struct GNUNET_SCHEDULER_Task *task)
 {
-  struct Task *t;
-  struct Task *prev;
   enum GNUNET_SCHEDULER_Priority p;
-  int to;
   void *ret;
 
-  GNUNET_assert (NULL != active_task);
-  to = 0;
-  prev = NULL;
-  t = pending;
-  while (NULL != t)
+  GNUNET_assert ( (NULL != active_task) ||
+      (GNUNET_NO == task->lifeness) );
+  if (! task->in_ready_list)
   {
-    if (t->id == task)
-      break;
-    prev = t;
-    t = t->next;
-  }
-  if (NULL == t)
-  {
-    prev = NULL;
-    to = 1;
-    t = pending_timeout;
-    while (t != NULL)
-    {
-      if (t->id == task)
-        break;
-      prev = t;
-      t = t->next;
-    }
-    if (pending_timeout_last == t)
-      pending_timeout_last = NULL;
-  }
-  p = 0;
-  while (NULL == t)
-  {
-    p++;
-    if (p >= GNUNET_SCHEDULER_PRIORITY_COUNT)
-    {
-      LOG (GNUNET_ERROR_TYPE_ERROR,
-           _("Attempt to cancel dead task %llu!\n"),
-           (unsigned long long) task);
-      GNUNET_assert (0);
-    }
-    prev = NULL;
-    t = ready[p];
-    while (NULL != t)
+    if ( (-1 == task->read_fd) &&
+         (-1 == task->write_fd) &&
+         (NULL == task->read_set) &&
+         (NULL == task->write_set) )
     {
-      if (t->id == task)
-      {
-        ready_count--;
-        break;
-      }
-      prev = t;
-      t = t->next;
-    }
-  }
-  if (NULL == prev)
-  {
-    if (0 == p)
-    {
-      if (0 == to)
-      {
-        pending = t->next;
-      }
+      if (GNUNET_YES == task->on_shutdown)
+  GNUNET_CONTAINER_DLL_remove (shutdown_head,
+             shutdown_tail,
+             task);
       else
-      {
-        pending_timeout = t->next;
-      }
+  GNUNET_CONTAINER_DLL_remove (pending_timeout_head,
+             pending_timeout_tail,
+             task);
+      if (task == pending_timeout_last)
+        pending_timeout_last = NULL;
     }
     else
     {
-      ready[p] = t->next;
+      scheduler_multi_function_call(task, scheduler_driver->del);
     }
   }
   else
   {
-    prev->next = t->next;
+    p = check_priority (task->priority);
+    GNUNET_CONTAINER_DLL_remove (ready_head[p],
+                                 ready_tail[p],
+                                 task);
+    ready_count--;
   }
-  ret = t->callback_cls;
+  ret = task->callback_cls;
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Canceling task: %llu / %p\n",
-       task,
-       t->callback_cls);
-  destroy_task (t);
+       "Canceling task %p\n",
+       task);
+  destroy_task (task);
   return ret;
 }
 
 
+/**
+ * Initialize backtrace data for task @a t
+ *
+ * @param t task to initialize
+ */
+static void
+init_backtrace (struct GNUNET_SCHEDULER_Task *t)
+{
+#if EXECINFO
+  void *backtrace_array[MAX_TRACE_DEPTH];
+
+  t->num_backtrace_strings
+    = backtrace (backtrace_array, MAX_TRACE_DEPTH);
+  t->backtrace_strings =
+      backtrace_symbols (backtrace_array,
+       t->num_backtrace_strings);
+  dump_backtrace (t);
+#endif
+}
+
+
 /**
  * Continue the current execution with the given function.  This is
  * similar to the other "add" functions except that there is no delay
@@ -1005,30 +1188,21 @@ GNUNET_SCHEDULER_cancel (GNUNET_SCHEDULER_TaskIdentifier task)
  * @param priority priority to use for the task
  */
 void
-GNUNET_SCHEDULER_add_continuation_with_priority (GNUNET_SCHEDULER_Task task, void *task_cls,
-                                                enum GNUNET_SCHEDULER_Reason reason,
-                                                enum GNUNET_SCHEDULER_Priority priority)
+GNUNET_SCHEDULER_add_with_reason_and_priority (GNUNET_SCHEDULER_TaskCallback task,
+                                               void *task_cls,
+                                               enum GNUNET_SCHEDULER_Reason reason,
+                                               enum GNUNET_SCHEDULER_Priority priority)
 {
-  struct Task *t;
-
-#if EXECINFO
-  void *backtrace_array[50];
-#endif
+  struct GNUNET_SCHEDULER_Task *t;
 
   GNUNET_assert (NULL != task);
   GNUNET_assert ((NULL != active_task) ||
                  (GNUNET_SCHEDULER_REASON_STARTUP == reason));
-  t = GNUNET_new (struct Task);
-#if EXECINFO
-  t->num_backtrace_strings = backtrace (backtrace_array, 50);
-  t->backtrace_strings =
-      backtrace_symbols (backtrace_array, t->num_backtrace_strings);
-#endif
+  t = GNUNET_new (struct GNUNET_SCHEDULER_Task);
   t->read_fd = -1;
   t->write_fd = -1;
   t->callback = task;
   t->callback_cls = task_cls;
-  t->id = ++last_id;
 #if PROFILE_DELAYS
   t->start_time = GNUNET_TIME_absolute_get ();
 #endif
@@ -1036,136 +1210,156 @@ GNUNET_SCHEDULER_add_continuation_with_priority (GNUNET_SCHEDULER_Task task, voi
   t->priority = priority;
   t->lifeness = current_lifeness;
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Adding continuation task: %llu / %p\n",
-       t->id,
-       t->callback_cls);
+       "Adding continuation task %p\n",
+       t);
+  init_backtrace (t);
   queue_ready_task (t);
 }
 
 
 /**
- * Continue the current execution with the given function.  This is
- * similar to the other "add" functions except that there is no delay
- * and the reason code can be specified.
- *
- * @param task main function of the task
- * @param task_cls closure for @a task
- * @param reason reason for task invocation
- */
-void
-GNUNET_SCHEDULER_add_continuation (GNUNET_SCHEDULER_Task task, void *task_cls,
-                                   enum GNUNET_SCHEDULER_Reason reason)
-{
-  GNUNET_SCHEDULER_add_continuation_with_priority (task, task_cls,
-                                                  reason,
-                                                  GNUNET_SCHEDULER_PRIORITY_DEFAULT);
-}
-
-
-/**
- * Schedule a new task to be run with a specified priority.
- *
- * @param prio how important is the new task?
- * @param task main function of the @a task
- * @param task_cls closure of task
- * @return unique task identifier for the job
- *         only valid until @a task is started!
- */
-GNUNET_SCHEDULER_TaskIdentifier
-GNUNET_SCHEDULER_add_with_priority (enum GNUNET_SCHEDULER_Priority prio,
-                                    GNUNET_SCHEDULER_Task task, void *task_cls)
-{
-  return GNUNET_SCHEDULER_add_select (prio,
-                                      GNUNET_TIME_UNIT_ZERO, NULL, NULL, task,
-                                      task_cls);
-}
-
-
-
-/**
- * Schedule a new task to be run with a specified delay.  The task
- * will be scheduled for execution once the delay has expired.
+ * Schedule a new task to be run at the specified time.  The task
+ * will be scheduled for execution at time @a at.
  *
- * @param delay when should this operation time out? Use
- *        #GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param at time when the operation should run
  * @param priority priority to use for the task
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
-GNUNET_SCHEDULER_add_delayed_with_priority (struct GNUNET_TIME_Relative delay,
-                                           enum GNUNET_SCHEDULER_Priority priority,
-                                           GNUNET_SCHEDULER_Task task, void *task_cls)
+struct GNUNET_SCHEDULER_Task *
+GNUNET_SCHEDULER_add_at_with_priority (struct GNUNET_TIME_Absolute at,
+                                       enum GNUNET_SCHEDULER_Priority priority,
+                                       GNUNET_SCHEDULER_TaskCallback task,
+                                       void *task_cls)
 {
-  struct Task *t;
-  struct Task *pos;
-  struct Task *prev;
-
-#if EXECINFO
-  void *backtrace_array[MAX_TRACE_DEPTH];
-#endif
+  struct GNUNET_SCHEDULER_Task *t;
+  struct GNUNET_SCHEDULER_Task *pos;
+  struct GNUNET_SCHEDULER_Task *prev;
 
   GNUNET_assert (NULL != active_task);
   GNUNET_assert (NULL != task);
-  t = GNUNET_new (struct Task);
+  t = GNUNET_new (struct GNUNET_SCHEDULER_Task);
   t->callback = task;
   t->callback_cls = task_cls;
-#if EXECINFO
-  t->num_backtrace_strings = backtrace (backtrace_array, MAX_TRACE_DEPTH);
-  t->backtrace_strings =
-      backtrace_symbols (backtrace_array, t->num_backtrace_strings);
-#endif
   t->read_fd = -1;
   t->write_fd = -1;
-  t->id = ++last_id;
 #if PROFILE_DELAYS
   t->start_time = GNUNET_TIME_absolute_get ();
 #endif
-  t->timeout = GNUNET_TIME_relative_to_absolute (delay);
+  t->timeout = at;
   t->priority = priority;
   t->lifeness = current_lifeness;
   /* try tail first (optimization in case we are
    * appending to a long list of tasks with timeouts) */
-  prev = pending_timeout_last;
-  if (prev != NULL)
+  if ( (NULL == pending_timeout_head) ||
+       (at.abs_value_us < pending_timeout_head->timeout.abs_value_us) )
   {
-    if (prev->timeout.abs_value_us > t->timeout.abs_value_us)
-      prev = NULL;
-    else
-      pos = prev->next;         /* heuristic success! */
-  }
-  if (prev == NULL)
-  {
-    /* heuristic failed, do traversal of timeout list */
-    pos = pending_timeout;
+    GNUNET_CONTAINER_DLL_insert (pending_timeout_head,
+                                 pending_timeout_tail,
+                                 t);
   }
-  while ((pos != NULL) &&
-         ((pos->timeout.abs_value_us <= t->timeout.abs_value_us) ||
-          (0 != pos->reason)))
+  else
   {
-    prev = pos;
-    pos = pos->next;
+    /* first move from heuristic start backwards to before start time */
+    prev = pending_timeout_last;
+    while ( (NULL != prev) &&
+            (prev->timeout.abs_value_us > t->timeout.abs_value_us) )
+      prev = prev->prev;
+    /* now, move from heuristic start (or head of list) forward to insertion point */
+    if (NULL == prev)
+      pos = pending_timeout_head;
+    else
+      pos = prev->next;
+    while ( (NULL != pos) &&
+            ( (pos->timeout.abs_value_us <= t->timeout.abs_value_us) ||
+              (0 != pos->reason) ) )
+    {
+      prev = pos;
+      pos = pos->next;
+    }
+    GNUNET_CONTAINER_DLL_insert_after (pending_timeout_head,
+                                       pending_timeout_tail,
+                                       prev,
+                                       t);
   }
-  if (prev == NULL)
-    pending_timeout = t;
-  else
-    prev->next = t;
-  t->next = pos;
-  /* hyper-optimization... */
+  /* finally, update heuristic insertion point to last insertion... */
   pending_timeout_last = t;
 
-  LOG (GNUNET_ERROR_TYPE_DEBUG, "Adding task: %llu / %p\n", t->id,
-       t->callback_cls);
-#if EXECINFO
-  int i;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Adding task: %p\n",
+       t);
+  init_backtrace (t);
+  return t;
+}
 
-  for (i = 0; i < t->num_backtrace_strings; i++)
-    LOG (GNUNET_ERROR_TYPE_DEBUG, "Task %llu trace %d: %s\n", t->id, i,
-         t->backtrace_strings[i]);
-#endif
-  return t->id;
+
+/**
+ * Schedule a new task to be run with a specified delay.  The task
+ * will be scheduled for execution once the delay has expired.
+ *
+ * @param delay when should this operation time out?
+ * @param priority priority to use for the task
+ * @param task main function of the task
+ * @param task_cls closure of @a task
+ * @return unique task identifier for the job
+ *         only valid until @a task is started!
+ */
+struct GNUNET_SCHEDULER_Task *
+GNUNET_SCHEDULER_add_delayed_with_priority (struct GNUNET_TIME_Relative delay,
+              enum GNUNET_SCHEDULER_Priority priority,
+              GNUNET_SCHEDULER_TaskCallback task,
+                                            void *task_cls)
+{
+  return GNUNET_SCHEDULER_add_at_with_priority (GNUNET_TIME_relative_to_absolute (delay),
+                                                priority,
+                                                task,
+                                                task_cls);
+}
+
+
+/**
+ * Schedule a new task to be run with a specified priority.
+ *
+ * @param prio how important is the new task?
+ * @param task main function of the task
+ * @param task_cls closure of @a task
+ * @return unique task identifier for the job
+ *         only valid until @a task is started!
+ */
+struct GNUNET_SCHEDULER_Task *
+GNUNET_SCHEDULER_add_with_priority (enum GNUNET_SCHEDULER_Priority prio,
+                                    GNUNET_SCHEDULER_TaskCallback task,
+                                    void *task_cls)
+{
+  return GNUNET_SCHEDULER_add_delayed_with_priority (GNUNET_TIME_UNIT_ZERO,
+                                                     prio,
+                                                     task,
+                                                     task_cls);
+}
+
+
+/**
+ * Schedule a new task to be run at the specified time.  The task
+ * will be scheduled for execution once specified time has been
+ * reached. It will be run with the DEFAULT priority.
+ *
+ * @param at time at which this operation should run
+ * @param task main function of the task
+ * @param task_cls closure of @a task
+ * @return unique task identifier for the job
+ *         only valid until @a task is started!
+ */
+struct GNUNET_SCHEDULER_Task *
+GNUNET_SCHEDULER_add_at (struct GNUNET_TIME_Absolute at,
+                         GNUNET_SCHEDULER_TaskCallback task,
+                         void *task_cls)
+{
+  return GNUNET_SCHEDULER_add_at_with_priority (at,
+                                                GNUNET_SCHEDULER_PRIORITY_DEFAULT,
+                                                task,
+                                                task_cls);
 }
 
 
@@ -1174,20 +1368,21 @@ GNUNET_SCHEDULER_add_delayed_with_priority (struct GNUNET_TIME_Relative delay,
  * will be scheduled for execution once the delay has expired. It
  * will be run with the DEFAULT priority.
  *
- * @param delay when should this operation time out? Use
- *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param task main function of the task
- * @param task_cls closure of task
+ * @param task_cls closure of @a task
  * @return unique task identifier for the job
- *         only valid until "task" is started!
+ *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_delayed (struct GNUNET_TIME_Relative delay,
-                              GNUNET_SCHEDULER_Task task, void *task_cls)
+                              GNUNET_SCHEDULER_TaskCallback task,
+            void *task_cls)
 {
   return GNUNET_SCHEDULER_add_delayed_with_priority (delay,
-                                                    GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-                                                    task, task_cls);
+                 GNUNET_SCHEDULER_PRIORITY_DEFAULT,
+                 task,
+                                                     task_cls);
 }
 
 
@@ -1204,12 +1399,56 @@ GNUNET_SCHEDULER_add_delayed (struct GNUNET_TIME_Relative delay,
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
- *         only valid until "task" is started!
+ *         only valid until @a task is started!
+ */
+struct GNUNET_SCHEDULER_Task *
+GNUNET_SCHEDULER_add_now (GNUNET_SCHEDULER_TaskCallback task,
+        void *task_cls)
+{
+  return GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_ZERO,
+               task,
+               task_cls);
+}
+
+
+/**
+ * Schedule a new task to be run on shutdown, that is when a CTRL-C
+ * signal is received, or when #GNUNET_SCHEDULER_shutdown() is being
+ * invoked.
+ *
+ * @param task main function of the task
+ * @param task_cls closure of @a task
+ * @return unique task identifier for the job
+ *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
-GNUNET_SCHEDULER_add_now (GNUNET_SCHEDULER_Task task, void *task_cls)
+struct GNUNET_SCHEDULER_Task *
+GNUNET_SCHEDULER_add_shutdown (GNUNET_SCHEDULER_TaskCallback task,
+             void *task_cls)
 {
-  return GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_ZERO, task, task_cls);
+  struct GNUNET_SCHEDULER_Task *t;
+
+  GNUNET_assert (NULL != active_task);
+  GNUNET_assert (NULL != task);
+  t = GNUNET_new (struct GNUNET_SCHEDULER_Task);
+  t->callback = task;
+  t->callback_cls = task_cls;
+  t->read_fd = -1;
+  t->write_fd = -1;
+#if PROFILE_DELAYS
+  t->start_time = GNUNET_TIME_absolute_get ();
+#endif
+  t->timeout = GNUNET_TIME_UNIT_FOREVER_ABS;
+  t->priority = GNUNET_SCHEDULER_PRIORITY_SHUTDOWN;
+  t->on_shutdown = GNUNET_YES;
+  t->lifeness = GNUNET_YES;
+  GNUNET_CONTAINER_DLL_insert (shutdown_head,
+             shutdown_tail,
+             t);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Adding task: %p\n",
+       t);
+  init_backtrace (t);
+  return t;
 }
 
 
@@ -1227,23 +1466,33 @@ GNUNET_SCHEDULER_add_now (GNUNET_SCHEDULER_Task task, void *task_cls)
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_now_with_lifeness (int lifeness,
-                                        GNUNET_SCHEDULER_Task task,
+                                        GNUNET_SCHEDULER_TaskCallback task,
                                         void *task_cls)
 {
-  GNUNET_SCHEDULER_TaskIdentifier ret;
-
-  ret =
-      GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-                                   GNUNET_TIME_UNIT_ZERO, NULL, NULL, task,
-                                   task_cls);
-  GNUNET_assert (pending->id == ret);
-  pending->lifeness = lifeness;
+  struct GNUNET_SCHEDULER_Task *ret;
+
+  ret = GNUNET_SCHEDULER_add_now (task, task_cls);
+  ret->lifeness = lifeness;
   return ret;
 }
 
 
+
+int scheduler_multi_function_call(struct GNUNET_SCHEDULER_Task *t, int (*driver_func)())
+{
+  if (t->fds_len > 1){
+    int success = GNUNET_YES;
+    for (int i = 0; i < t->fds_len;i++){
+      success = driver_func(scheduler_driver->cls, t , t->fds+i) && success;
+    }
+    return success;
+  }else{
+    return driver_func(scheduler_driver->cls, t , t->fds);
+  }
+}
+
 /**
  * Schedule a new task to be run with a specified delay or when any of
  * the specified file descriptor sets is ready.  The delay can be used
@@ -1257,43 +1506,39 @@ GNUNET_SCHEDULER_add_now_with_lifeness (int lifeness,
  * (prerequisite-run)
  * && (delay-ready
  *     || any-rs-ready
- *     || any-ws-ready
- *     || shutdown-active )
+ *     || any-ws-ready)
  * </code>
  *
- * @param delay how long should we wait? Use #GNUNET_TIME_UNIT_FOREVER_REL for "forever",
- *        which means that the task will only be run after we receive SIGTERM
+ * @param delay how long should we wait?
  * @param priority priority to use
  * @param rfd file descriptor we want to read (can be -1)
  * @param wfd file descriptors we want to write (can be -1)
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
- *         only valid until "task" is started!
+ *         only valid until @a task is started!
  */
 #ifndef MINGW
-static GNUNET_SCHEDULER_TaskIdentifier
+static struct GNUNET_SCHEDULER_Task *
 add_without_sets (struct GNUNET_TIME_Relative delay,
-                 enum GNUNET_SCHEDULER_Priority priority,
-                 int rfd, int wfd,
-                  GNUNET_SCHEDULER_Task task, void *task_cls)
+                  enum GNUNET_SCHEDULER_Priority priority,
+                  const struct GNUNET_NETWORK_Handle *read_nh,
+                  const struct GNUNET_NETWORK_Handle *write_nh,
+                  const struct GNUNET_DISK_FileHandle *read_fh,
+                  const struct GNUNET_DISK_FileHandle *write_fh,
+                  //int rfd,
+                  //int wfd,
+                  GNUNET_SCHEDULER_TaskCallback task,
+                  void *task_cls)
 {
-  struct Task *t;
-
-#if EXECINFO
-  void *backtrace_array[MAX_TRACE_DEPTH];
-#endif
+  struct GNUNET_SCHEDULER_Task *t;
 
   GNUNET_assert (NULL != active_task);
   GNUNET_assert (NULL != task);
-  t = GNUNET_new (struct Task);
+  t= initFdInfo (read_nh, write_nh, read_fh, write_fh);
+
   t->callback = task;
   t->callback_cls = task_cls;
-#if EXECINFO
-  t->num_backtrace_strings = backtrace (backtrace_array, MAX_TRACE_DEPTH);
-  t->backtrace_strings =
-      backtrace_symbols (backtrace_array, t->num_backtrace_strings);
-#endif
 #if DEBUG_FDS
   if (-1 != rfd)
   {
@@ -1304,14 +1549,7 @@ add_without_sets (struct GNUNET_TIME_Relative delay,
       LOG (GNUNET_ERROR_TYPE_ERROR,
            "Got invalid file descriptor %d!\n",
            rfd);
-#if EXECINFO
-      int i;
-
-      for (i = 0; i < t->num_backtrace_strings; i++)
-        LOG (GNUNET_ERROR_TYPE_DEBUG,
-             "Trace: %s\n",
-             t->backtrace_strings[i]);
-#endif
+      init_backtrace (t);
       GNUNET_assert (0);
     }
   }
@@ -1324,51 +1562,34 @@ add_without_sets (struct GNUNET_TIME_Relative delay,
       LOG (GNUNET_ERROR_TYPE_ERROR,
            "Got invalid file descriptor %d!\n",
            wfd);
-#if EXECINFO
-      int i;
-
-      for (i = 0; i < t->num_backtrace_strings; i++)
-        LOG (GNUNET_ERROR_TYPE_DEBUG,
-             "Trace: %s\n",
-             t->backtrace_strings[i]);
-#endif
+      init_backtrace (t);
       GNUNET_assert (0);
     }
   }
 #endif
-  t->read_fd = rfd;
-  GNUNET_assert (wfd >= -1);
-  t->write_fd = wfd;
-  t->id = ++last_id;
+
 #if PROFILE_DELAYS
   t->start_time = GNUNET_TIME_absolute_get ();
 #endif
   t->timeout = GNUNET_TIME_relative_to_absolute (delay);
   t->priority = check_priority ((priority == GNUNET_SCHEDULER_PRIORITY_KEEP) ? current_priority : priority);
   t->lifeness = current_lifeness;
-  t->next = pending;
-  pending = t;
-  max_priority_added = GNUNET_MAX (max_priority_added, t->priority);
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Adding task: %llu / %p\n",
-       t->id,
-       t->callback_cls);
-#if EXECINFO
-  int i;
 
-  for (i = 0; i < t->num_backtrace_strings; i++)
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Task %llu trace %d: %s\n",
-         t->id,
-         i,
-         t->backtrace_strings[i]);
-#endif
-  return t->id;
+
+
+  scheduler_multi_function_call(t, scheduler_driver->add);
+
+  max_priority_added = GNUNET_MAX (max_priority_added,
+                                   t->priority);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Adding task %p\n",
+       t);
+  init_backtrace (t);
+  return t;
 }
 #endif
 
 
-
 /**
  * Schedule a new task to be run with a specified delay or when the
  * specified file descriptor is ready for reading.  The delay can be
@@ -1376,22 +1597,22 @@ add_without_sets (struct GNUNET_TIME_Relative delay,
  * scheduled for execution once either the delay has expired or the
  * socket operation is ready.  It will be run with the DEFAULT priority.
  *
- * @param delay when should this operation time out? Use
- *        #GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param rfd read file-descriptor
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_read_net (struct GNUNET_TIME_Relative delay,
                                struct GNUNET_NETWORK_Handle *rfd,
-                               GNUNET_SCHEDULER_Task task, void *task_cls)
+                               GNUNET_SCHEDULER_TaskCallback task,
+                               void *task_cls)
 {
   return GNUNET_SCHEDULER_add_read_net_with_priority (delay,
-                                                     GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-                                                     rfd, task, task_cls);
+                  GNUNET_SCHEDULER_PRIORITY_DEFAULT,
+                  rfd, task, task_cls);
 }
 
 
@@ -1403,8 +1624,7 @@ GNUNET_SCHEDULER_add_read_net (struct GNUNET_TIME_Relative delay,
  * either the delay has expired or the socket operation is ready.  It
  * will be run with the DEFAULT priority.
  *
- * @param delay when should this operation time out? Use
- *        #GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param priority priority to use for the task
  * @param rfd read file-descriptor
  * @param task main function of the task
@@ -1412,16 +1632,18 @@ GNUNET_SCHEDULER_add_read_net (struct GNUNET_TIME_Relative delay,
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_read_net_with_priority (struct GNUNET_TIME_Relative delay,
-                                            enum GNUNET_SCHEDULER_Priority priority,
-                                            struct GNUNET_NETWORK_Handle *rfd,
-                                            GNUNET_SCHEDULER_Task task, void *task_cls)
+               enum GNUNET_SCHEDULER_Priority priority,
+               struct GNUNET_NETWORK_Handle *rfd,
+               GNUNET_SCHEDULER_TaskCallback task,
+                                             void *task_cls)
 {
-  return GNUNET_SCHEDULER_add_net_with_priority (
-      delay, priority,
-      rfd, true, false,
-      task, task_cls);
+  return GNUNET_SCHEDULER_add_net_with_priority (delay, priority,
+                                                 rfd,
+                                                 GNUNET_YES,
+                                                 GNUNET_NO,
+                                                 task, task_cls);
 }
 
 
@@ -1433,23 +1655,24 @@ GNUNET_SCHEDULER_add_read_net_with_priority (struct GNUNET_TIME_Relative delay,
  * socket operation is ready.  It will be run with the priority of
  * the calling task.
  *
- * @param delay when should this operation time out? Use
- *        #GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param wfd write file-descriptor
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_write_net (struct GNUNET_TIME_Relative delay,
                                 struct GNUNET_NETWORK_Handle *wfd,
-                                GNUNET_SCHEDULER_Task task, void *task_cls)
+                                GNUNET_SCHEDULER_TaskCallback task,
+                                void *task_cls)
 {
-  return GNUNET_SCHEDULER_add_net_with_priority (
-      delay, GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-      wfd, false, true,
-      task, task_cls);
+  return GNUNET_SCHEDULER_add_net_with_priority (delay,
+                                                 GNUNET_SCHEDULER_PRIORITY_DEFAULT,
+                                                 wfd,
+                                                 GNUNET_NO, GNUNET_YES,
+                                                 task, task_cls);
 }
 
 /**
@@ -1459,8 +1682,7 @@ GNUNET_SCHEDULER_add_write_net (struct GNUNET_TIME_Relative delay,
  * scheduled for execution once either the delay has expired or the
  * socket operation is ready.
  *
- * @param delay when should this operation time out? Use
- *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param priority priority of the task
  * @param fd file-descriptor
  * @param on_read whether to poll the file-descriptor for readability
@@ -1470,18 +1692,20 @@ GNUNET_SCHEDULER_add_write_net (struct GNUNET_TIME_Relative delay,
  * @return unique task identifier for the job
  *         only valid until "task" is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_net_with_priority  (struct GNUNET_TIME_Relative delay,
                                          enum GNUNET_SCHEDULER_Priority priority,
                                          struct GNUNET_NETWORK_Handle *fd,
-                                         bool on_read, bool on_write,
-                                         GNUNET_SCHEDULER_Task task, void *task_cls)
+                                         int on_read,
+                                         int on_write,
+                                         GNUNET_SCHEDULER_TaskCallback task,
+                                         void *task_cls)
 {
 #if MINGW
   struct GNUNET_NETWORK_FDSet *s;
-  GNUNET_SCHEDULER_TaskIdentifier ret;
+  struct GNUNET_SCHEDULER_Task * ret;
 
-  GNUNET_assert (fd != NULL);
+  GNUNET_assert (NULL != fd);
   s = GNUNET_NETWORK_fdset_create ();
   GNUNET_NETWORK_fdset_set (s, fd);
   ret = GNUNET_SCHEDULER_add_select (
@@ -1492,12 +1716,14 @@ GNUNET_SCHEDULER_add_net_with_priority  (struct GNUNET_TIME_Relative delay,
   GNUNET_NETWORK_fdset_destroy (s);
   return ret;
 #else
+  GNUNET_assert (on_read || on_write);
   GNUNET_assert (GNUNET_NETWORK_get_fd (fd) >= 0);
-  return add_without_sets (
-      delay, priority,
-      on_read  ? GNUNET_NETWORK_get_fd (fd) : -1,
-      on_write ? GNUNET_NETWORK_get_fd (fd) : -1,
-      task, task_cls);
+  return add_without_sets (delay, priority,
+                           on_read  ? fd : NULL,
+                           on_write ? fd : NULL,
+                           NULL,
+                           NULL,
+                           task, task_cls);
 #endif
 }
 
@@ -1509,22 +1735,21 @@ GNUNET_SCHEDULER_add_net_with_priority  (struct GNUNET_TIME_Relative delay,
  * scheduled for execution once either the delay has expired or the
  * socket operation is ready. It will be run with the DEFAULT priority.
  *
- * @param delay when should this operation time out? Use
- *        #GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param rfd read file-descriptor
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_read_file (struct GNUNET_TIME_Relative delay,
                                 const struct GNUNET_DISK_FileHandle *rfd,
-                                GNUNET_SCHEDULER_Task task, void *task_cls)
+                                GNUNET_SCHEDULER_TaskCallback task, void *task_cls)
 {
   return GNUNET_SCHEDULER_add_file_with_priority (
       delay, GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-      rfd, true, false,
+      rfd, GNUNET_YES, GNUNET_NO,
       task, task_cls);
 }
 
@@ -1536,25 +1761,25 @@ GNUNET_SCHEDULER_add_read_file (struct GNUNET_TIME_Relative delay,
  * scheduled for execution once either the delay has expired or the
  * socket operation is ready. It will be run with the DEFAULT priority.
  *
- * @param delay when should this operation time out? Use
- *        #GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param wfd write file-descriptor
  * @param task main function of the task
  * @param task_cls closure of @a task
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_write_file (struct GNUNET_TIME_Relative delay,
                                  const struct GNUNET_DISK_FileHandle *wfd,
-                                 GNUNET_SCHEDULER_Task task, void *task_cls)
+                                 GNUNET_SCHEDULER_TaskCallback task, void *task_cls)
 {
   return GNUNET_SCHEDULER_add_file_with_priority (
       delay, GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-      wfd, false, true,
+      wfd, GNUNET_NO, GNUNET_YES,
       task, task_cls);
 }
 
+
 /**
  * Schedule a new task to be run with a specified delay or when the
  * specified file descriptor is ready.  The delay can be
@@ -1562,29 +1787,28 @@ GNUNET_SCHEDULER_add_write_file (struct GNUNET_TIME_Relative delay,
  * scheduled for execution once either the delay has expired or the
  * socket operation is ready.
  *
- * @param delay when should this operation time out? Use
- *        GNUNET_TIME_UNIT_FOREVER_REL for "on shutdown"
+ * @param delay when should this operation time out?
  * @param priority priority of the task
  * @param fd file-descriptor
  * @param on_read whether to poll the file-descriptor for readability
  * @param on_write whether to poll the file-descriptor for writability
  * @param task main function of the task
- * @param task_cls closure of task
+ * @param task_cls closure of @a task
  * @return unique task identifier for the job
- *         only valid until "task" is started!
+ *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_file_with_priority (struct GNUNET_TIME_Relative delay,
                                          enum GNUNET_SCHEDULER_Priority priority,
                                          const struct GNUNET_DISK_FileHandle *fd,
-                                         bool on_read, bool on_write,
-                                         GNUNET_SCHEDULER_Task task, void *task_cls)
+                                         int on_read, int on_write,
+                                         GNUNET_SCHEDULER_TaskCallback task, void *task_cls)
 {
 #if MINGW
   struct GNUNET_NETWORK_FDSet *s;
-  GNUNET_SCHEDULER_TaskIdentifier ret;
+  struct GNUNET_SCHEDULER_Task * ret;
 
-  GNUNET_assert (fd != NULL);
+  GNUNET_assert (NULL != fd);
   s = GNUNET_NETWORK_fdset_create ();
   GNUNET_NETWORK_fdset_handle_set (s, fd);
   ret = GNUNET_SCHEDULER_add_select (
@@ -1595,15 +1819,14 @@ GNUNET_SCHEDULER_add_file_with_priority (struct GNUNET_TIME_Relative delay,
   GNUNET_NETWORK_fdset_destroy (s);
   return ret;
 #else
-  int real_fd;
-
-  GNUNET_DISK_internal_file_handle_ (fd, &real_fd, sizeof (int));
-  GNUNET_assert (real_fd > 0);
-  return add_without_sets (
-      delay, priority,
-      on_read  ? real_fd : -1,
-      on_write ? real_fd : -1,
-      task, task_cls);
+  GNUNET_assert (on_read || on_write);
+  GNUNET_assert(fd->fd >= 0);
+  return add_without_sets (delay, priority,
+                           NULL,
+                           NULL,
+                           on_read ? fd : NULL,
+                           on_write ? fd : NULL,
+                           task, task_cls);
 #endif
 }
 
@@ -1621,13 +1844,11 @@ GNUNET_SCHEDULER_add_file_with_priority (struct GNUNET_TIME_Relative delay,
  * (prerequisite-run)
  * && (delay-ready
  *     || any-rs-ready
- *     || any-ws-ready
- *     || (shutdown-active && run-on-shutdown) )
+ *     || any-ws-ready) )
  * </code>
  *
  * @param prio how important is this task?
- * @param delay how long should we wait? Use #GNUNET_TIME_UNIT_FOREVER_REL for "forever",
- *        which means that the task will only be run after we receive SIGTERM
+ * @param delay how long should we wait?
  * @param rs set of file descriptors we want to read (can be NULL)
  * @param ws set of file descriptors we want to write (can be NULL)
  * @param task main function of the task
@@ -1635,28 +1856,27 @@ GNUNET_SCHEDULER_add_file_with_priority (struct GNUNET_TIME_Relative delay,
  * @return unique task identifier for the job
  *         only valid until @a task is started!
  */
-GNUNET_SCHEDULER_TaskIdentifier
+struct GNUNET_SCHEDULER_Task *
 GNUNET_SCHEDULER_add_select (enum GNUNET_SCHEDULER_Priority prio,
                              struct GNUNET_TIME_Relative delay,
                              const struct GNUNET_NETWORK_FDSet *rs,
                              const struct GNUNET_NETWORK_FDSet *ws,
-                             GNUNET_SCHEDULER_Task task, void *task_cls)
+                             GNUNET_SCHEDULER_TaskCallback task,
+                             void *task_cls)
 {
-  struct Task *t;
-#if EXECINFO
-  void *backtrace_array[MAX_TRACE_DEPTH];
-#endif
-
+  struct GNUNET_SCHEDULER_Task *t;
+
+  if ( (NULL == rs) &&
+       (NULL == ws) )
+    return GNUNET_SCHEDULER_add_delayed_with_priority (delay,
+                                                       prio,
+                                                       task,
+                                                       task_cls);
   GNUNET_assert (NULL != active_task);
   GNUNET_assert (NULL != task);
-  t = GNUNET_new (struct Task);
+  t = GNUNET_new (struct GNUNET_SCHEDULER_Task);
   t->callback = task;
   t->callback_cls = task_cls;
-#if EXECINFO
-  t->num_backtrace_strings = backtrace (backtrace_array, MAX_TRACE_DEPTH);
-  t->backtrace_strings =
-      backtrace_symbols (backtrace_array, t->num_backtrace_strings);
-#endif
   t->read_fd = -1;
   t->write_fd = -1;
   if (NULL != rs)
@@ -1669,7 +1889,6 @@ GNUNET_SCHEDULER_add_select (enum GNUNET_SCHEDULER_Priority prio,
     t->write_set = GNUNET_NETWORK_fdset_create ();
     GNUNET_NETWORK_fdset_copy (t->write_set, ws);
   }
-  t->id = ++last_id;
 #if PROFILE_DELAYS
   t->start_time = GNUNET_TIME_absolute_get ();
 #endif
@@ -1679,23 +1898,338 @@ GNUNET_SCHEDULER_add_select (enum GNUNET_SCHEDULER_Priority prio,
                        GNUNET_SCHEDULER_PRIORITY_KEEP) ? current_priority :
                       prio);
   t->lifeness = current_lifeness;
-  t->next = pending;
-  pending = t;
-  max_priority_added = GNUNET_MAX (max_priority_added, t->priority);
+
+  scheduler_multi_function_call(t, scheduler_driver->add);
+
+  max_priority_added = GNUNET_MAX (max_priority_added,
+           t->priority);
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Adding task: %llu / %p\n",
-       t->id,
-       t->callback_cls);
-#if EXECINFO
-  int i;
+       "Adding task %p\n",
+       t);
+  init_backtrace (t);
+  return t;
+}
 
-  for (i = 0; i < t->num_backtrace_strings; i++)
+
+/**
+ * Function used by event-loop implementations to signal the scheduler
+ * that a particular @a task is ready due to an event of type @a et.
+ *
+ * This function will then queue the task to notify the application
+ * that the task is ready (with the respective priority).
+ *
+ * @param task the task that is ready, NULL for wake up calls
+ * @param et information about why the task is ready
+ */
+void
+GNUNET_SCHEDULER_task_ready (struct GNUNET_SCHEDULER_Task *task,
+           enum GNUNET_SCHEDULER_EventType et)
+{
+  enum GNUNET_SCHEDULER_Reason reason;
+  struct GNUNET_TIME_Absolute now;
+
+  now = GNUNET_TIME_absolute_get ();
+  reason = task->reason;
+  if (now.abs_value_us >= task->timeout.abs_value_us)
+    reason |= GNUNET_SCHEDULER_REASON_TIMEOUT;
+  if ( (0 == (reason & GNUNET_SCHEDULER_REASON_READ_READY)) &&
+       (0 != (GNUNET_SCHEDULER_ET_IN & et)) )
+    reason |= GNUNET_SCHEDULER_REASON_READ_READY;
+  if ( (0 == (reason & GNUNET_SCHEDULER_REASON_WRITE_READY)) &&
+       (0 != (GNUNET_SCHEDULER_ET_OUT & et)) )
+    reason |= GNUNET_SCHEDULER_REASON_WRITE_READY;
+  reason |= GNUNET_SCHEDULER_REASON_PREREQ_DONE;
+  task->reason = reason;
+  task->fds = &task->fdx;
+  task->fdx.et = et;
+  task->fds_len = 1;
+  queue_ready_task (task);
+}
+
+
+/**
+ * Function called by the driver to tell the scheduler to run some of
+ * the tasks that are ready.  This function may return even though
+ * there are tasks left to run just to give other tasks a chance as
+ * well.  If we return #GNUNET_YES, the driver should call this
+ * function again as soon as possible, while if we return #GNUNET_NO
+ * it must block until the operating system has more work as the
+ * scheduler has no more work to do right now.
+ *
+ * @param sh scheduler handle that was given to the `loop`
+ * @return #GNUNET_OK if there are more tasks that are ready,
+ *          and thus we would like to run more (yield to avoid
+ *          blocking other activities for too long)
+ *         #GNUNET_NO if we are done running tasks (yield to block)
+ *         #GNUNET_SYSERR on error
+ */
+int
+GNUNET_SCHEDULER_run_from_driver (struct GNUNET_SCHEDULER_Handle *sh)
+{
+  enum GNUNET_SCHEDULER_Priority p;
+  struct GNUNET_SCHEDULER_Task *pos;
+  struct GNUNET_TIME_Absolute now;
+
+  /* check for tasks that reached the timeout! */
+  now = GNUNET_TIME_absolute_get ();
+  while (NULL != (pos = pending_timeout_head))
+  {
+    if (now.abs_value_us >= pos->timeout.abs_value_us)
+      pos->reason |= GNUNET_SCHEDULER_REASON_TIMEOUT;
+    if (0 == pos->reason)
+      break;
+    GNUNET_CONTAINER_DLL_remove (pending_timeout_head,
+                                 pending_timeout_tail,
+                                 pos);
+    if (pending_timeout_last == pos)
+      pending_timeout_last = NULL;
+    queue_ready_task (pos);
+  }
+
+  if (0 == ready_count)
+    return GNUNET_NO;
+
+  /* find out which task priority level we are going to
+     process this time */
+  max_priority_added = GNUNET_SCHEDULER_PRIORITY_KEEP;
+  GNUNET_assert (NULL == ready_head[GNUNET_SCHEDULER_PRIORITY_KEEP]);
+  /* yes, p>0 is correct, 0 is "KEEP" which should
+   * always be an empty queue (see assertion)! */
+  for (p = GNUNET_SCHEDULER_PRIORITY_COUNT - 1; p > 0; p--)
+  {
+    pos = ready_head[p];
+    if (NULL != pos)
+      break;
+  }
+  GNUNET_assert (NULL != pos);        /* ready_count wrong? */
+
+  /* process all tasks at this priority level, then yield */
+  while (NULL != (pos = ready_head[p]))
+  {
+    GNUNET_CONTAINER_DLL_remove (ready_head[p],
+         ready_tail[p],
+         pos);
+    ready_count--;
+    current_priority = pos->priority;
+    current_lifeness = pos->lifeness;
+    active_task = pos;
+#if PROFILE_DELAYS
+    if (GNUNET_TIME_absolute_get_duration (pos->start_time).rel_value_us >
+  DELAY_THRESHOLD.rel_value_us)
+    {
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+     "Task %p took %s to be scheduled\n",
+     pos,
+     GNUNET_STRINGS_relative_time_to_string (GNUNET_TIME_absolute_get_duration (pos->start_time),
+               GNUNET_YES));
+    }
+#endif
+    tc.reason = pos->reason;
+    GNUNET_NETWORK_fdset_zero (sh->rs);
+    GNUNET_NETWORK_fdset_zero (sh->ws);
+    tc.fds_len = pos->fds_len;
+    tc.fds = pos->fds;
+    tc.read_ready = (NULL == pos->read_set) ? sh->rs : pos->read_set;
+    if ( (-1 != pos->read_fd) &&
+   (0 != (pos->reason & GNUNET_SCHEDULER_REASON_READ_READY)) )
+      GNUNET_NETWORK_fdset_set_native (sh->rs,
+               pos->read_fd);
+    tc.write_ready = (NULL == pos->write_set) ? sh->ws : pos->write_set;
+    if ((-1 != pos->write_fd) &&
+  (0 != (pos->reason & GNUNET_SCHEDULER_REASON_WRITE_READY)))
+      GNUNET_NETWORK_fdset_set_native (sh->ws,
+               pos->write_fd);
     LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Task %llu trace %d: %s\n",
-         t->id, i,
-         t->backtrace_strings[i]);
+   "Running task: %p\n",
+   pos);
+    pos->callback (pos->callback_cls);
+    active_task = NULL;
+    dump_backtrace (pos);
+    destroy_task (pos);
+    tasks_run++;
+  }
+  if (0 == ready_count)
+    return GNUNET_NO;
+  return GNUNET_OK;
+}
+
+
+/**
+ * Initialize and run scheduler.  This function will return when all
+ * tasks have completed.  On systems with signals, receiving a SIGTERM
+ * (and other similar signals) will cause #GNUNET_SCHEDULER_shutdown
+ * to be run after the active task is complete.  As a result, SIGTERM
+ * causes all shutdown tasks to be scheduled with reason
+ * #GNUNET_SCHEDULER_REASON_SHUTDOWN.  (However, tasks added
+ * afterwards will execute normally!).  Note that any particular
+ * signal will only shut down one scheduler; applications should
+ * always only create a single scheduler.
+ *
+ * @param driver drive to use for the event loop
+ * @param task task to run first (and immediately)
+ * @param task_cls closure of @a task
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
+ */
+int
+GNUNET_SCHEDULER_run_with_driver (const struct GNUNET_SCHEDULER_Driver *driver,
+          GNUNET_SCHEDULER_TaskCallback task,
+          void *task_cls)
+{
+  int ret;
+  struct GNUNET_SCHEDULER_Handle sh;
+  struct GNUNET_SIGNAL_Context *shc_int;
+  struct GNUNET_SIGNAL_Context *shc_term;
+#if (SIGTERM != GNUNET_TERM_SIG)
+  struct GNUNET_SIGNAL_Context *shc_gterm;
+#endif
+#ifndef MINGW
+  struct GNUNET_SIGNAL_Context *shc_quit;
+  struct GNUNET_SIGNAL_Context *shc_hup;
+  struct GNUNET_SIGNAL_Context *shc_pipe;
+#endif
+  struct GNUNET_SCHEDULER_Task tsk;
+  const struct GNUNET_DISK_FileHandle *pr;
+  scheduler_driver = driver;
+
+  /* general set-up */
+  GNUNET_assert (NULL == active_task);
+  GNUNET_assert (NULL == shutdown_pipe_handle);
+  shutdown_pipe_handle = GNUNET_DISK_pipe (GNUNET_NO,
+                                           GNUNET_NO,
+                                           GNUNET_NO,
+                                           GNUNET_NO);
+  GNUNET_assert (NULL != shutdown_pipe_handle);
+  pr = GNUNET_DISK_pipe_handle (shutdown_pipe_handle,
+                                GNUNET_DISK_PIPE_END_READ);
+  GNUNET_assert (NULL != pr);
+  my_pid = getpid ();
+
+  /* install signal handlers */
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Registering signal handlers\n");
+  shc_int = GNUNET_SIGNAL_handler_install (SIGINT,
+             &sighandler_shutdown);
+  shc_term = GNUNET_SIGNAL_handler_install (SIGTERM,
+              &sighandler_shutdown);
+#if (SIGTERM != GNUNET_TERM_SIG)
+  shc_gterm = GNUNET_SIGNAL_handler_install (GNUNET_TERM_SIG,
+               &sighandler_shutdown);
+#endif
+#ifndef MINGW
+  shc_pipe = GNUNET_SIGNAL_handler_install (SIGPIPE,
+              &sighandler_pipe);
+  shc_quit = GNUNET_SIGNAL_handler_install (SIGQUIT,
+              &sighandler_shutdown);
+  shc_hup = GNUNET_SIGNAL_handler_install (SIGHUP,
+             &sighandler_shutdown);
+#endif
+
+  /* Setup initial tasks */
+  current_priority = GNUNET_SCHEDULER_PRIORITY_DEFAULT;
+  current_lifeness = GNUNET_YES;
+  memset (&tsk,
+    0,
+    sizeof (tsk));
+  active_task = &tsk;
+  tsk.sh = &sh;
+  GNUNET_SCHEDULER_add_with_reason_and_priority (task,
+                                                 task_cls,
+                                                 GNUNET_SCHEDULER_REASON_STARTUP,
+                                                 GNUNET_SCHEDULER_PRIORITY_DEFAULT);
+  GNUNET_SCHEDULER_add_now_with_lifeness (GNUNET_NO,
+                                          &GNUNET_OS_install_parent_control_handler,
+                                          NULL);
+  active_task = NULL;
+  driver->set_wakeup (driver->cls,
+          GNUNET_TIME_absolute_get ());
+
+  /* begin main event loop */
+  sh.rs = GNUNET_NETWORK_fdset_create ();
+  sh.ws = GNUNET_NETWORK_fdset_create ();
+  GNUNET_NETWORK_fdset_handle_set (sh.rs, pr);
+  sh.driver = driver;
+  ret = driver->loop (driver->cls,
+          &sh);
+  GNUNET_NETWORK_fdset_destroy (sh.rs);
+  GNUNET_NETWORK_fdset_destroy (sh.ws);
+
+  /* uninstall signal handlers */
+  GNUNET_SIGNAL_handler_uninstall (shc_int);
+  GNUNET_SIGNAL_handler_uninstall (shc_term);
+#if (SIGTERM != GNUNET_TERM_SIG)
+  GNUNET_SIGNAL_handler_uninstall (shc_gterm);
 #endif
-  return t->id;
+#ifndef MINGW
+  GNUNET_SIGNAL_handler_uninstall (shc_pipe);
+  GNUNET_SIGNAL_handler_uninstall (shc_quit);
+  GNUNET_SIGNAL_handler_uninstall (shc_hup);
+#endif
+  GNUNET_DISK_pipe_close (shutdown_pipe_handle);
+  shutdown_pipe_handle = NULL;
+  return ret;
+}
+
+int
+select_add(void *cls,
+ struct GNUNET_SCHEDULER_Task *task,
+ struct GNUNET_SCHEDULER_FdInfo *fdi){
+
+  GNUNET_CONTAINER_DLL_insert (pending_head,
+                               pending_tail,
+                               task);
+
+}
+
+int
+select_del(void *cls,
+ struct GNUNET_SCHEDULER_Task *task,
+ struct GNUNET_SCHEDULER_FdInfo *fdi){
+
+  GNUNET_CONTAINER_DLL_remove (pending_head,
+                               pending_tail,
+                               task);
+
+}
+
+
+int
+select_loop(void *cls,
+        struct GNUNET_SCHEDULER_Handle *sh){
+
+  while_live(sh->rs, sh->ws);
+
+}
+
+static void
+select_set_wakeup(void *cls,
+                   struct GNUNET_TIME_Absolute dt){
+
+
+
 }
 
+
+/**
+ * Obtain the driver for using select() as the event loop.
+ *
+ * @return NULL on error
+ */
+const struct GNUNET_SCHEDULER_Driver *
+GNUNET_SCHEDULER_driver_select ()
+{
+
+  struct GNUNET_SCHEDULER_Driver *select_driver;
+
+  select_driver = GNUNET_new (struct GNUNET_SCHEDULER_Driver);
+
+  select_driver->loop = &select_loop;
+  select_driver->add = &select_add;
+  select_driver->del = &select_del;
+  select_driver->set_wakeup = &select_set_wakeup;
+
+
+  return select_driver;
+}
+
+
 /* end of scheduler.c */