From ec4bbf35a159b5d019d6acd84aa5753b794bb7ee Mon Sep 17 00:00:00 2001
From: Benjamin Schubert <ben.c.schubert@gmail.com>
Date: Mon, 11 Feb 2019 15:20:00 +0000
Subject: Cleanup internal Loader cache after loading elements

---
 buildstream/_loader/loader.py | 19 +++++++++++++++++++
 buildstream/_project.py       |  2 ++
 buildstream/element.py        | 15 +++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/buildstream/_loader/loader.py b/buildstream/_loader/loader.py
index d0cfa8522..17d7c63fb 100644
--- a/buildstream/_loader/loader.py
+++ b/buildstream/_loader/loader.py
@@ -152,8 +152,27 @@ class Loader():
             #
             ret.append(loader._collect_element(element))
 
+        self._clean_caches()
+
         return ret
 
+    # clean_caches()
+    #
+    # Clean internal loader caches, recursively
+    #
+    # When loading the elements, the loaders use caches in order to not load the
+    # same element twice. These are kept after loading and prevent garbage
+    # collection. Cleaning them explicitely is required.
+    #
+    def _clean_caches(self):
+        for loader in self._loaders.values():
+            # value may be None with nested junctions without overrides
+            if loader is not None:
+                loader._clean_caches()
+
+        self._meta_elements = {}
+        self._elements = {}
+
     ###########################################
     #            Private Methods              #
     ###########################################
diff --git a/buildstream/_project.py b/buildstream/_project.py
index 028bdcc9f..92ac8cab5 100644
--- a/buildstream/_project.py
+++ b/buildstream/_project.py
@@ -358,6 +358,8 @@ class Project():
                 for meta in meta_elements
             ]
 
+        Element._clear_meta_elements_cache()
+
         # Now warn about any redundant source references which may have
         # been discovered in the resolve() phase.
         redundant_refs = Element._get_redundant_source_refs()
diff --git a/buildstream/element.py b/buildstream/element.py
index a3bf59dc6..5ecc25ab2 100644
--- a/buildstream/element.py
+++ b/buildstream/element.py
@@ -966,6 +966,21 @@ class Element(Plugin):
 
         return element
 
+    # _clear_meta_elements_cache()
+    #
+    # Clear the internal meta elements cache.
+    #
+    # When loading elements from meta, we cache already instantiated elements
+    # in order to not have to load the same elements twice.
+    # This clears the cache.
+    #
+    # It should be called whenever we are done loading all elements in order
+    # to save memory.
+    #
+    @classmethod
+    def _clear_meta_elements_cache(cls):
+        cls.__instantiated_elements = {}
+
     # _get_redundant_source_refs()
     #
     # Fetches a list of (Source, ref) tuples of all the Sources
-- 
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