Merge branch 'bschubert/optimize-loading-multiple-targets' into 'master'

loader.py: Optimize sorting of elements when they are multiple targets

See merge request BuildStream/buildstream!1794

2 files changed, 16 insertions, 3 deletions

diff --git a/src/buildstream/_loader/loadelement.pyx b/src/buildstream/_loader/loadelement.pyx
index fb1dd1d15..31c3aef1a 100644
--- a/src/buildstream/_loader/loadelement.pyx
+++ b/src/buildstream/_loader/loadelement.pyx
@@ -212,12 +212,21 @@ def _dependency_cmp(Dependency dep_a, Dependency dep_b):
 #
 # Args:
 #    element (LoadElement): The element to sort
+#    visited (set): a list of elements that should not be treated because
+#                   because they already have been treated.
+#                   This is useful when wanting to sort dependencies of
+#                   multiple top level elements that might have a common
+#                   part.
 #
-def sort_dependencies(LoadElement element):
+def sort_dependencies(LoadElement element, set visited):
     cdef list working_elements = [element]
-    cdef set visited = set(working_elements)
     cdef Dependency dep
 
+    if element in visited:
+        return
+
+    visited.add(element)
+
     # Now dependency sort, we ensure that if any direct dependency
     # directly or indirectly depends on another direct dependency,
     # it is found later in the list.
diff --git a/src/buildstream/_loader/loader.py b/src/buildstream/_loader/loader.py
index 3b18af691..0c6c725c7 100644
--- a/src/buildstream/_loader/loader.py
+++ b/src/buildstream/_loader/loader.py
@@ -141,10 +141,14 @@ class Loader:
         #
         # Sort direct dependencies of elements by their dependency ordering
         #
+
+        # Keep a list of all visited elements, to not sort twice the same
+        visited_elements = set()
+
         for element in target_elements:
             loader = element._loader
             with PROFILER.profile(Topics.SORT_DEPENDENCIES, element.name):
-                loadelement.sort_dependencies(element)
+                loadelement.sort_dependencies(element, visited_elements)
 
             # Finally, wrap what we have into LoadElements and return the target
             #