queue.py: Use heapq for the ready queuejennis/push_based_pipeline

This patch includes setting a _depth to each element
once the pipeline has been sorted. This is necessary
as we need to store elements in the heapq sorted by
their depth.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/buildstream/element.py b/src/buildstream/element.py
index 355773f76..84c8f20ff 100644
--- a/src/buildstream/element.py
+++ b/src/buildstream/element.py
@@ -244,6 +244,8 @@ class Element(Plugin):
         self.__can_query_cache_callback = None        # Callback to PullQueue/FetchQueue
         self.__buildable_callback = None              # Callback to BuildQueue
 
+        self._depth = None                            # Depth of Element in its current dependency graph
+
         # Ensure we have loaded this class's defaults
         self.__init_defaults(project, plugin_conf, meta.kind, meta.is_junction)
 
@@ -2310,6 +2312,16 @@ class Element(Plugin):
     def _set_buildable_callback(self, callback):
         self.__buildable_callback = callback
 
+    # _set_depth()
+    #
+    # Set the depth of the Element.
+    #
+    # The depth represents the position of the Element within the current
+    # session's dependency graph. A depth of zero represents the bottommost element.
+    #
+    def _set_depth(self, depth):
+        self._depth = depth
+
     #############################################################
     #                   Private Local Methods                   #
     #############################################################