From b587d85a5fc8f706362396dc347830f16797b1f2 Mon Sep 17 00:00:00 2001
From: Mattias Ellert <mattias.ellert@physics.uu.se>
Date: Tue, 16 Jan 2018 10:25:50 +0100
Subject: [PATCH] Reduce the needed memory for compilation

The linking of rootcling_stage1 and libCling requires a lot of memory.
Since these are linked from mostly the same objects, the build is ready
to link them at the same time. If you make a parallel build this means
that the two targets that require the most amount of memory are being
linked in parallel. This exhausts the available memory, and the
computer starts swapping.

This adds a dependency of one of the targets to the other. The dependency is
not really there since it is not needed for building, but it prevents the
two memory consuming targets to be built in parallel.

A similar dependency existed before the code latest code changes
(see commit 2638f6fc7f54b0995f2f9d60363daaf8aae2386e), then between
rootcling and libCling.
---
 core/metacling/src/CMakeLists.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/core/metacling/src/CMakeLists.txt b/core/metacling/src/CMakeLists.txt
index eccd77681d..df941eb3b7 100644
--- a/core/metacling/src/CMakeLists.txt
+++ b/core/metacling/src/CMakeLists.txt
@@ -86,6 +86,10 @@ ROOT_LINKER_LIBRARY(Cling
         $<TARGET_OBJECTS:MetaCling>
         LIBRARIES ${CLING_LIBRARIES} ${LINK_LIBS} ${CLING_PLUGIN_LINK_LIBS})
 
+# The dependency on rootcling_stage1 was added to prevent Cling (libCling) and
+# rootcling_stage1 from being linked in parallel.
+# This avoids doing two memory consuming operations in parallel.
+add_dependencies(Cling rootcling_stage1)
 
 if(MSVC)
   set_target_properties(Cling PROPERTIES WINDOWS_EXPORT_ALL_SYMBOLS TRUE)
-- 
2.20.1