[master] 699d1b9 esi and waitinglist

[Nils Goroll]

commit 699d1b9dc34352735c741645dcd02ecee29d6d7b
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed Sep 14 15:31:49 2016 +0200

    esi and waitinglist

diff --git a/doc/sphinx/whats-new/changes-5.0.rst b/doc/sphinx/whats-new/changes-5.0.rst
index 13f99ea..9da62ee 100644
--- a/doc/sphinx/whats-new/changes-5.0.rst
+++ b/doc/sphinx/whats-new/changes-5.0.rst
@@ -155,6 +155,19 @@ but a GET or HEAD and without creating an appropriate cache key doing
 so is almost guaranteed to be wrong.
 
 
+ESI and Backend Request Coalescing ("waitinglist") Improvement
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Previously, ESI subrequests depending on objects being fetched from
+the backed used polling, which typically added some ~5ms of processing
+time to such subrequests and could lead to starvation effects in
+extreme corner cases.
+
+The waitinglist logic for ESI subrequests now uses condition variables
+to trigger immediate continuation of ESI processing when an object
+being waited for becomes available.
+
+
 Default VCL search path
 ~~~~~~~~~~~~~~~~~~~~~~~