From 72f815d5355de82919818ee5f42c6463715b9e84 Mon Sep 17 00:00:00 2001
From: Tatsuhiro Tsujikawa <tatsuhiro.t@gmail.com>
Date: Mon, 7 Dec 2015 22:43:15 +0900
Subject: [PATCH] Update descendant_last_cycle on
 nghttp2_stream_next_outbound_item

Previously, we updated descendant_last_cycle in
nghttp2_stream_reschedule, which is called after non-zero DATA frame.
But this was not optimal since we still had old descendant_last_cycle,
and new stream was scheduled based on it.  Now descendant_last_cycle
is updated in nghttp2_stream_next_outbound_item, which is called when
stream with highest priority is selected from queue.  And new stream
is scheduled based on it.  This commit also removes 0-reset of
descendant_last_cycle and cycle in nghttp2_stream_reschedule.  This
could help making them lower, so that they are not overflow.  But
there is a pattern that it doesn't work, and we are not sure they are
really useful at this moment.
---
 lib/nghttp2_stream.c | 28 +++++++++++-----------------
 lib/nghttp2_stream.h |  3 ++-
 2 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/lib/nghttp2_stream.c b/lib/nghttp2_stream.c
index 54219a4d..06b64850 100644
--- a/lib/nghttp2_stream.c
+++ b/lib/nghttp2_stream.c
@@ -207,25 +207,13 @@ void nghttp2_stream_reschedule(nghttp2_stream *stream) {
   dep_stream = stream->dep_prev;
 
   for (; dep_stream; stream = dep_stream, dep_stream = dep_stream->dep_prev) {
-    if (nghttp2_pq_size(&dep_stream->obq) == 1) {
-      dep_stream->descendant_last_cycle = 0;
-      stream->cycle = 0;
-    } else {
-      /* We update descendant_last_cycle here, and we don't do it when
-         no data is written for stream.  This effectively means that
-         we treat these streams as if they are not scheduled at all.
-         This does not cause disruption in scheduling machinery.  It
-         just makes new streams scheduled a bit early. */
-      dep_stream->descendant_last_cycle = stream->cycle;
+    nghttp2_pq_remove(&dep_stream->obq, &stream->pq_entry);
 
-      nghttp2_pq_remove(&dep_stream->obq, &stream->pq_entry);
+    stream->cycle =
+        stream_next_cycle(stream, dep_stream->descendant_last_cycle);
+    stream->seq = dep_stream->descendant_next_seq++;
 
-      stream->cycle =
-          stream_next_cycle(stream, dep_stream->descendant_last_cycle);
-      stream->seq = dep_stream->descendant_next_seq++;
-
-      nghttp2_pq_push(&dep_stream->obq, &stream->pq_entry);
-    }
+    nghttp2_pq_push(&dep_stream->obq, &stream->pq_entry);
 
     DEBUGF(fprintf(stderr, "stream: stream=%d obq resched cycle=%ld\n",
                    stream->stream_id, stream->cycle));
@@ -861,9 +849,15 @@ int nghttp2_stream_in_dep_tree(nghttp2_stream *stream) {
 nghttp2_outbound_item *
 nghttp2_stream_next_outbound_item(nghttp2_stream *stream) {
   nghttp2_pq_entry *ent;
+  nghttp2_stream *si;
 
   for (;;) {
     if (stream_active(stream)) {
+      /* Update ascendant's descendant_last_cycle here, so that we can
+         assure that new stream is scheduled based on it. */
+      for (si = stream; si->dep_prev; si = si->dep_prev) {
+        si->dep_prev->descendant_last_cycle = si->cycle;
+      }
       return stream->item;
     }
     ent = nghttp2_pq_top(&stream->obq);
diff --git a/lib/nghttp2_stream.h b/lib/nghttp2_stream.h
index e2dddefa..bbb8b9f3 100644
--- a/lib/nghttp2_stream.h
+++ b/lib/nghttp2_stream.h
@@ -419,7 +419,8 @@ int nghttp2_stream_in_dep_tree(nghttp2_stream *stream);
 void nghttp2_stream_reschedule(nghttp2_stream *stream);
 
 /*
- * Returns a stream which has highest priority.
+ * Returns a stream which has highest priority, updating
+ * descendant_last_cycle of selected stream's ancestors.
  */
 nghttp2_outbound_item *
 nghttp2_stream_next_outbound_item(nghttp2_stream *stream);