Share stream_group weight among streams marked as top

lib/nghttp2_session.c

@@ -686,7 +686,7 @@ int nghttp2_session_add_frame(nghttp2_session *session,
 
     stream = nghttp2_session_get_stream(session, data_frame->hd.stream_id);
     if(stream) {
-      item->weight = stream->stream_group->weight;
+      item->weight = nghttp2_stream_group_shared_wait(stream->stream_group);
 
       rv = nghttp2_stream_attach_data(stream, item, &session->ob_pq);
     }
@@ -2087,7 +2087,8 @@ static int nghttp2_session_after_frame_sent(nghttp2_session *session)
     assert(stream);
     next_item = nghttp2_session_get_next_ob_item(session);
 
-    outbound_item_cycle_weight(aob->item, stream->stream_group->weight);
+    outbound_item_cycle_weight
+      (aob->item, nghttp2_stream_group_shared_wait(stream->stream_group));
 
     /* If priority of this stream is higher or equal to other stream
        waiting at the top of the queue, we continue to send this

lib/nghttp2_stream.c

@@ -27,6 +27,8 @@
 #include <assert.h>
 #include <stdio.h>
 
+#include "nghttp2_helper.h"
+
 void nghttp2_stream_init(nghttp2_stream *stream, int32_t stream_id,
                          uint8_t flags,
                          nghttp2_stream_state initial_state,
@@ -58,6 +60,7 @@ void nghttp2_stream_init(nghttp2_stream *stream, int32_t stream_id,
   stream->stream_group = NULL;
   stream->dpri = NGHTTP2_STREAM_DPRI_NO_DATA;
   stream->num_substreams = 1;
+  stream->num_subtop = 0;
 }
 
 void nghttp2_stream_free(nghttp2_stream *stream)
@@ -101,6 +104,23 @@ static nghttp2_stream* stream_update_dep_length(nghttp2_stream *stream,
   return stream;
 }
 
+static nghttp2_stream* stream_update_dep_both_length(nghttp2_stream *stream,
+                                                     ssize_t delta_stream,
+                                                     ssize_t delta_top)
+{
+  stream->num_substreams += delta_stream;
+  stream->num_subtop += delta_top;
+
+  stream = stream_first_sib(stream);
+
+  if(stream->dep_prev) {
+    return stream_update_dep_both_length(stream->dep_prev, delta_stream,
+                                         delta_top);
+  }
+
+  return stream;
+}
+
 static void stream_update_dep_set_rest_stream_group
 (nghttp2_stream *stream, nghttp2_stream_group *stream_group)
 {
@@ -129,6 +149,8 @@ static void stream_update_dep_set_rest(nghttp2_stream *stream)
     return;
   }
 
+  stream->num_subtop = 0;
+
   if(stream->dpri == NGHTTP2_STREAM_DPRI_TOP) {
     stream->dpri = NGHTTP2_STREAM_DPRI_REST;
 
@@ -145,22 +167,33 @@ static void stream_update_dep_set_rest(nghttp2_stream *stream)
  * Performs dfs starting |stream|, search stream which can become
  * NGHTTP2_STREAM_DPRI_TOP and queues its data.
  *
- * This function returns 0 if it succeeds, or one of the following
+ * This function returns the number of stream marked as
- * negative error codes:
+ * NGHTTP2_STREAM_DPRI_TOP (including already marked as such) if it
+ * succeeds, or one of the following negative error codes:
  *
  * NGHTTP2_ERR_NOMEM
  *     Out of memory.
  */
-static int stream_update_dep_set_top(nghttp2_stream *stream, nghttp2_pq *pq)
+static ssize_t stream_update_dep_set_top(nghttp2_stream *stream,
+                                         nghttp2_pq *pq)
 {
-  int rv;
+  ssize_t rv;
+  ssize_t num_top;
 
   if(stream == NULL) {
     return 0;
   }
 
   if(stream->dpri == NGHTTP2_STREAM_DPRI_TOP) {
-    return stream_update_dep_set_top(stream->sib_next, pq);
+    rv = stream_update_dep_set_top(stream->sib_next, pq);
+
+    if(rv < 0) {
+      return rv;
+    }
+
+    stream->num_subtop = 1;
+
+    return stream->num_subtop + rv;
   }
 
   if(stream->dpri == NGHTTP2_STREAM_DPRI_REST) {
@@ -180,25 +213,44 @@ static int stream_update_dep_set_top(nghttp2_stream *stream, nghttp2_pq *pq)
 
     stream->dpri = NGHTTP2_STREAM_DPRI_TOP;
 
-    return stream_update_dep_set_top(stream->sib_next, pq);
+    rv = stream_update_dep_set_top(stream->sib_next, pq);
+
+    if(rv < 0) {
+      return rv;
+    }
+
+    stream->num_subtop = 1;
+
+    return stream->num_subtop + rv;
   }
 
   assert(stream->dpri == NGHTTP2_STREAM_DPRI_NO_DATA);
 
   rv = stream_update_dep_set_top(stream->sib_next, pq);
 
-  if(rv != 0) {
+  if(rv < 0) {
     return rv;
   }
 
-  return stream_update_dep_set_top(stream->dep_next, pq);
+  num_top = rv;
+
+  rv = stream_update_dep_set_top(stream->dep_next, pq);
+
+  if(rv < 0) {
+    return rv;
   }
 
-static int stream_update_dep_on_attach_data(nghttp2_stream *stream,
+  stream->num_subtop = rv;
+
+  return stream->num_subtop + num_top;
+}
+
+static ssize_t stream_update_dep_on_attach_data(nghttp2_stream *stream,
                                                 nghttp2_pq *pq)
 {
-  int rv;
+  ssize_t rv;
   nghttp2_stream *root_stream;
+  ssize_t old_num_subtop;
 
   stream->dpri = NGHTTP2_STREAM_DPRI_REST;
 
@@ -208,18 +260,27 @@ static int stream_update_dep_on_attach_data(nghttp2_stream *stream,
 
   DEBUGF(fprintf(stderr, "root=%p, stream=%p\n", root_stream, stream));
 
+  old_num_subtop = root_stream->num_subtop;
+
   rv = stream_update_dep_set_top(root_stream, pq);
 
-  if(rv != 0) {
+  if(rv < 0) {
     return rv;
   }
 
+  nghttp2_stream_group_update_num_top
+    (root_stream->stream_group, root_stream->num_subtop - old_num_subtop);
+
   return 0;
 }
 
 static int stream_update_dep_on_detach_data(nghttp2_stream *stream,
                                             nghttp2_pq *pq)
 {
+  ssize_t rv;
+  nghttp2_stream *root_stream;
+  ssize_t old_num_subtop;
+
   if(stream->dpri != NGHTTP2_STREAM_DPRI_TOP) {
     stream->dpri = NGHTTP2_STREAM_DPRI_NO_DATA;
 
@@ -228,7 +289,20 @@ static int stream_update_dep_on_detach_data(nghttp2_stream *stream,
 
   stream->dpri = NGHTTP2_STREAM_DPRI_NO_DATA;
 
-  return stream_update_dep_set_top(stream->dep_next, pq);
+  root_stream = nghttp2_stream_get_dep_root(stream);
+
+  old_num_subtop = root_stream->num_subtop;
+
+  rv = stream_update_dep_set_top(root_stream, pq);
+
+  if(rv < 0) {
+    return rv;
+  }
+
+  nghttp2_stream_group_update_num_top
+    (root_stream->stream_group, root_stream->num_subtop - old_num_subtop);
+
+  return 0;
 }
 
 int nghttp2_stream_attach_data(nghttp2_stream *stream,
@@ -509,6 +583,8 @@ int nghttp2_stream_dep_insert_subtree(nghttp2_stream *dep_stream,
   nghttp2_stream *root_stream;
   nghttp2_stream *si;
   size_t delta_substreams;
+  ssize_t old_num_subtop;
+  ssize_t rv;
 
   DEBUGF(fprintf(stderr, "stream: dep_insert_subtree dep_stream(%p)=%d "
                  "stream(%p)=%d\n",
@@ -517,6 +593,9 @@ int nghttp2_stream_dep_insert_subtree(nghttp2_stream *dep_stream,
 
   delta_substreams = stream->num_substreams;
 
+  nghttp2_stream_group_update_num_top
+    (stream->stream_group, -stream->num_subtop);
+
   stream_update_dep_set_rest_stream_group(stream, dep_stream->stream_group);
 
   if(dep_stream->dep_next) {
@@ -549,7 +628,18 @@ int nghttp2_stream_dep_insert_subtree(nghttp2_stream *dep_stream,
 
   root_stream = stream_update_dep_length(dep_stream, delta_substreams);
 
-  return stream_update_dep_set_top(root_stream, pq);
+  old_num_subtop = root_stream->num_subtop;
+
+  rv = stream_update_dep_set_top(root_stream, pq);
+
+  if(rv < 0) {
+    return rv;
+  }
+
+  nghttp2_stream_group_update_num_top
+    (root_stream->stream_group, root_stream->num_subtop - old_num_subtop);
+
+  return 0;
 }
 
 int nghttp2_stream_dep_add_subtree(nghttp2_stream *dep_stream,
@@ -558,12 +648,17 @@ int nghttp2_stream_dep_add_subtree(nghttp2_stream *dep_stream,
 {
   nghttp2_stream *last_sib;
   nghttp2_stream *root_stream;
+  ssize_t old_num_subtop;
+  ssize_t rv;
 
   DEBUGF(fprintf(stderr, "stream: dep_add_subtree dep_stream(%p)=%d "
                  "stream(%p)=%d\n",
                  dep_stream, dep_stream->stream_id,
                  stream, stream->stream_id));
 
+  nghttp2_stream_group_update_num_top
+    (stream->stream_group, -stream->num_subtop);
+
   stream_update_dep_set_rest_stream_group(stream, dep_stream->stream_group);
 
   if(dep_stream->dep_next) {
@@ -578,13 +673,29 @@ int nghttp2_stream_dep_add_subtree(nghttp2_stream *dep_stream,
 
   root_stream = stream_update_dep_length(dep_stream, stream->num_substreams);
 
-  return stream_update_dep_set_top(root_stream, pq);
+  old_num_subtop = root_stream->num_subtop;
+
+  rv = stream_update_dep_set_top(root_stream, pq);
+
+  if(rv < 0) {
+    return rv;
+  }
+
+  nghttp2_stream_group_update_num_top
+    (root_stream->stream_group, root_stream->num_subtop - old_num_subtop);
+
+  return 0;
 }
 
 void nghttp2_stream_dep_remove_subtree(nghttp2_stream *stream)
 {
   nghttp2_stream *prev, *next;
 
+  DEBUGF(fprintf(stderr, "stream: dep_remove_subtree stream(%p)=%d\n",
+                 stream, stream->stream_id));
+
+  /* Removing subtree does not change stream_group->num_top */
+
   if(stream->sib_prev) {
     prev = stream->sib_prev;
 
@@ -595,7 +706,8 @@ void nghttp2_stream_dep_remove_subtree(nghttp2_stream *stream)
 
     prev = stream_first_sib(prev);
     if(prev->dep_prev) {
-      stream_update_dep_length(prev->dep_prev, -stream->num_substreams);
+      stream_update_dep_both_length(prev->dep_prev, -stream->num_substreams,
+                                    -stream->num_subtop);
     }
   } else if(stream->dep_prev) {
     prev = stream->dep_prev;
@@ -609,7 +721,8 @@ void nghttp2_stream_dep_remove_subtree(nghttp2_stream *stream)
       next->sib_prev = NULL;
     }
 
-    stream_update_dep_length(prev, -stream->num_substreams);
+    stream_update_dep_both_length(prev, -stream->num_substreams,
+                                  -stream->num_subtop);
   }
 
   stream->sib_prev = NULL;
@@ -621,9 +734,29 @@ int nghttp2_stream_dep_make_root(nghttp2_stream_group *stream_group,
                                  nghttp2_stream *stream,
                                  nghttp2_pq *pq)
 {
+  ssize_t rv;
+
+  DEBUGF(fprintf(stderr, "stream: dep_make_root new_stream_group(%p)=%d, "
+                 "old_stream_group(%p)=%d, stream(%p)=%d\n",
+                 stream_group, stream_group->pri_group_id,
+                 stream->stream_group, stream->stream_group->pri_group_id,
+                 stream, stream->stream_id));
+
+  /* First update num_top of old stream_group */
+  nghttp2_stream_group_update_num_top
+    (stream->stream_group, -stream->num_subtop);
+
   stream_update_dep_set_rest_stream_group(stream, stream_group);
 
-  return stream_update_dep_set_top(stream, pq);
+  rv = stream_update_dep_set_top(stream, pq);
+
+  if(rv < 0) {
+    return rv;
+  }
+
+  nghttp2_stream_group_update_num_top(stream_group, stream->num_subtop);
+
+  return 0;
 }
 
 void nghttp2_stream_group_init(nghttp2_stream_group *stream_group,
@@ -633,6 +766,7 @@ void nghttp2_stream_group_init(nghttp2_stream_group *stream_group,
   nghttp2_map_entry_init(&stream_group->map_entry, pri_group_id);
 
   stream_group->num_streams = 0;
+  stream_group->num_top = 0;
   stream_group->pri_group_id = pri_group_id;
   stream_group->weight = weight;
 }
@@ -665,3 +799,24 @@ void nghttp2_stream_group_remove_stream(nghttp2_stream_group *stream_group,
 
   --stream_group->num_streams;
 }
+
+void nghttp2_stream_group_update_num_top(nghttp2_stream_group *stream_group,
+                                         ssize_t delta)
+{
+  DEBUGF(fprintf(stderr, "stream_group: stream_group(%p)=%d "
+                 "update num_top current=%zd, delta=%zd, after=%zd\n",
+                 stream_group->num_top, delta, stream_group->num_top + delta));
+
+  stream_group->num_top += delta;
+
+  assert(stream_group->num_top >= 0);
+}
+
+size_t nghttp2_stream_group_shared_wait(nghttp2_stream_group *stream_group)
+{
+  if(stream_group->num_top == 0) {
+    return 1;
+  }
+
+  return nghttp2_max(1, stream_group->weight / stream_group->num_top);
+}

lib/nghttp2_stream.h

@@ -138,8 +138,11 @@ struct nghttp2_stream {
   /* categorized priority of this stream.  Only stream bearing
      NGHTTP2_STREAM_DPRI_TOP can send DATA frame. */
   nghttp2_stream_dpri dpri;
-  /* the number of nodes in subtree */
+  /* the number of streams in subtree */
   size_t num_substreams;
+  /* the number of streams marked as NGHTTP2_STREAM_DPRI_TOP in
+     subtree */
+  ssize_t num_subtop;
   /* Current remote window size. This value is computed against the
      current initial window size of remote endpoint. */
   int32_t remote_window_size;
@@ -322,7 +325,8 @@ int nghttp2_stream_dep_add_subtree(nghttp2_stream *dep_stream,
 
 /*
  * Removes subtree whose root stream is |stream|.  Removing subtree
- * does not change dpri values.
+ * does not change dpri values and removed subtree is still in the
+ * same stream_group.
  *
  * This function returns 0 if it succeeds, or one of the following
  * negative error codes:
@@ -354,6 +358,8 @@ struct nghttp2_stream_group {
   nghttp2_map_entry map_entry;
   /* The number of streams this priority group contains */
   size_t num_streams;
+  /* The number of streams marked as NGHTTP2_STREAM_DPRI_TOP */
+  ssize_t num_top;
   /* The priority group ID */
   int32_t pri_group_id;
   /* The weight of this group */
@@ -378,4 +384,15 @@ void nghttp2_stream_group_add_stream(nghttp2_stream_group *stream_group,
 void nghttp2_stream_group_remove_stream(nghttp2_stream_group *stream_group,
                                         nghttp2_stream *stream);
 
+/*
+ * Updates |stream_group->num_top| += |delta|
+ */
+void nghttp2_stream_group_update_num_top(nghttp2_stream_group *stream_group,
+                                         ssize_t delta);
+
+/*
+ * Returns shared weight among the streams belongs to |stream_group|.
+ */
+size_t nghttp2_stream_group_shared_wait(nghttp2_stream_group *stream_group);
+
 #endif /* NGHTTP2_STREAM */

tests/nghttp2_session_test.c

@@ -5224,6 +5224,12 @@ void test_nghttp2_session_stream_attach_data(void)
 
   CU_ASSERT(1 == db->queued);
 
+  CU_ASSERT(1 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
   dc = create_data_ob_item();
 
   nghttp2_stream_attach_data(c, dc, &session->ob_pq);
@@ -5235,6 +5241,12 @@ void test_nghttp2_session_stream_attach_data(void)
 
   CU_ASSERT(1 == dc->queued);
 
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(2 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(1 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
   da = create_data_ob_item();
 
   nghttp2_stream_attach_data(a, da, &session->ob_pq);
@@ -5246,6 +5258,12 @@ void test_nghttp2_session_stream_attach_data(void)
 
   CU_ASSERT(1 == da->queued);
 
+  CU_ASSERT(1 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(0 == b->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
   nghttp2_stream_detach_data(a, &session->ob_pq);
 
   CU_ASSERT(NGHTTP2_STREAM_DPRI_NO_DATA == a->dpri);
@@ -5253,6 +5271,12 @@ void test_nghttp2_session_stream_attach_data(void)
   CU_ASSERT(NGHTTP2_STREAM_DPRI_TOP == c->dpri);
   CU_ASSERT(NGHTTP2_STREAM_DPRI_NO_DATA == d->dpri);
 
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(2 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(1 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
   dd = create_data_ob_item();
 
   nghttp2_stream_attach_data(d, dd, &session->ob_pq);
@@ -5264,6 +5288,12 @@ void test_nghttp2_session_stream_attach_data(void)
 
   CU_ASSERT(0 == dd->queued);
 
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(2 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(1 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
   nghttp2_stream_detach_data(c, &session->ob_pq);
 
   CU_ASSERT(NGHTTP2_STREAM_DPRI_NO_DATA == a->dpri);
@@ -5273,6 +5303,12 @@ void test_nghttp2_session_stream_attach_data(void)
 
   CU_ASSERT(1 == dd->queued);
 
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(2 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(1 == c->num_subtop);
+  CU_ASSERT(1 == d->num_subtop);
+
   nghttp2_session_del(session);
 }
 
@@ -5280,8 +5316,8 @@ void test_nghttp2_session_stream_attach_data_subtree(void)
 {
   nghttp2_session *session;
   nghttp2_session_callbacks callbacks;
-  nghttp2_stream *a, *b, *c, *d, *e, *f;
+  nghttp2_stream *a, *b, *c, *d, *e, *f, *g, *h;
-  nghttp2_outbound_item *db, *de;
+  nghttp2_outbound_item *db, *dd, *de;
 
   (void)d;
 
@@ -5296,8 +5332,9 @@ void test_nghttp2_session_stream_attach_data_subtree(void)
 
   e = open_stream(session, 9);
   f = open_stream_with_dep(session, 11, e);
-
+  /* gr.1     gr.9
-  /* a        e
+   *
+   * a        e
    * |        |
    * b--c     f
    *    |
@@ -5312,9 +5349,16 @@ void test_nghttp2_session_stream_attach_data_subtree(void)
 
   nghttp2_stream_attach_data(b, db, &session->ob_pq);
 
+  CU_ASSERT(1 == a->stream_group->num_top);
+  CU_ASSERT(1 == e->stream_group->num_top);
+
+  /* Insert subtree e under a */
+
   nghttp2_stream_dep_insert_subtree(a, e, &session->ob_pq);
 
-  /* a
+  /* gr.1
+   *
+   * a
    * |
    * e
    * |
@@ -5327,12 +5371,185 @@ void test_nghttp2_session_stream_attach_data_subtree(void)
   CU_ASSERT(NGHTTP2_STREAM_DPRI_TOP == e->dpri);
   CU_ASSERT(NGHTTP2_STREAM_DPRI_NO_DATA == f->dpri);
 
+  CU_ASSERT(1 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(0 == b->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  /* Remove subtree b */
+
   nghttp2_stream_dep_remove_subtree(b);
 
   nghttp2_stream_dep_make_root(b->stream_group, b, &session->ob_pq);
 
+  /* gr.1    gr.1
+   *
+   * a       b
+   * |
+   * e
+   * |
+   * f--c
+   *    |
+   *    d
+   */
+
   CU_ASSERT(NGHTTP2_STREAM_DPRI_TOP == b->dpri);
 
+  /* a and b are still same group */
+  CU_ASSERT(b->stream_group == a->stream_group);
+
+  CU_ASSERT(2 == b->stream_group->num_top);
+  CU_ASSERT(1 == b->num_subtop);
+
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  /* Remove subtree a */
+
+  nghttp2_stream_dep_remove_subtree(a);
+
+  nghttp2_stream_dep_make_root(a->stream_group, a, &session->ob_pq);
+
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  /* Remove subtree c */
+
+  nghttp2_stream_dep_remove_subtree(c);
+
+  nghttp2_stream_dep_make_root(c->stream_group, c, &session->ob_pq);
+
+  /* gr.1    gr.1  gr.1
+   *
+   * a       b     c
+   * |             |
+   * e             d
+   * |
+   * f
+   */
+
+  CU_ASSERT(2 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  dd = create_data_ob_item();
+
+  nghttp2_stream_attach_data(d, dd, &session->ob_pq);
+
+  CU_ASSERT(3 == a->stream_group->num_top);
+  CU_ASSERT(1 == c->num_subtop);
+  CU_ASSERT(1 == d->num_subtop);
+
+  /* Add subtree c to a */
+
+  nghttp2_stream_dep_add_subtree(a, c, &session->ob_pq);
+
+  /* gr.1    gr.1
+   *
+   * a       b
+   * |
+   * e--c
+   * |  |
+   * f  d
+   */
+
+  CU_ASSERT(3 == a->stream_group->num_top);
+  CU_ASSERT(2 == a->num_subtop);
+  CU_ASSERT(1 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(1 == c->num_subtop);
+  CU_ASSERT(1 == d->num_subtop);
+
+  /* Insert b under a */
+
+  nghttp2_stream_dep_insert_subtree(a, b, &session->ob_pq);
+
+  /* gr.1
+   *
+   * a
+   * |
+   * b
+   * |
+   * e--c
+   * |  |
+   * f  d
+   */
+
+  CU_ASSERT(1 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(0 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  g = open_stream(session, 13);
+  h = open_stream(session, 15);
+
+  nghttp2_stream_dep_make_root(a->stream_group, h, &session->ob_pq);
+
+  nghttp2_stream_dep_make_root(g->stream_group, a, &session->ob_pq);
+
+  /* gr.13   gr.13  gr.1
+   *
+   * a       g      h
+   * |
+   * b
+   * |
+   * e--c
+   * |  |
+   * f  d
+   */
+
+  CU_ASSERT(g->stream_group == a->stream_group);
+
+  CU_ASSERT(0 == h->stream_group->num_top);
+
+  CU_ASSERT(1 == a->stream_group->num_top);
+  CU_ASSERT(1 == a->num_subtop);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(0 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  /* Remove subtree b */
+
+  nghttp2_stream_dep_remove_subtree(b);
+
+  /* gr.13   gr.13  gr.13  gr.1
+   *
+   * b       a      g      h
+   * |
+   * e--c
+   * |  |
+   * f  d
+   */
+
+  CU_ASSERT(1 == b->stream_group->num_top);
+  CU_ASSERT(1 == b->num_subtop);
+  CU_ASSERT(0 == e->num_subtop);
+  CU_ASSERT(0 == f->num_subtop);
+  CU_ASSERT(0 == c->num_subtop);
+  CU_ASSERT(0 == d->num_subtop);
+
+  CU_ASSERT(0 == a->num_subtop);
+
   nghttp2_session_del(session);
 }