From 94f808b1fc0620eb35980211fc3a2759bbd6be42 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Mon, 29 Jul 2019 21:32:04 -0400
Subject: [PATCH] user guide: add Barriers section

---
 doc/user_guide.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/doc/user_guide.md b/doc/user_guide.md
index a8366f3..ce2583d 100644
--- a/doc/user_guide.md
+++ b/doc/user_guide.md
@@ -730,6 +730,18 @@ Post-build hooks are only invoked if the build operation was a success.
 
 Build hooks and post-build hooks can register new build targets.
 
+###> Barriers
+
+Normally Rscons will parallelize all builders.
+A barrier can be used to separate sets of build targets.
+All build targets registered before the barrier is created will be built before
+Rscons will schedule any build targets after the barrier.
+In other words, build targets are not parallelized across a barrier.
+
+```ruby
+env.barrier
+```
+
 ##> Extending Rscons
 
 ### Adding New Languages