Merge branch 'tristan/fix-cloned-plugin-ids-1.2' into 'bst-1.2'

Tristan/fix cloned plugin ids 1.2

See merge request BuildStream/buildstream!1315

2 files changed, 21 insertions, 10 deletions

diff --git a/buildstream/plugin.py b/buildstream/plugin.py
index 2c94c212c..fbcf249bb 100644
--- a/buildstream/plugin.py
+++ b/buildstream/plugin.py
@@ -149,8 +149,12 @@ class Plugin():
     # Unique id generator for Plugins
     #
     # Each plugin gets a unique id at creation.
-    # Ids are a monotically increasing integer
-    __id_generator = itertools.count()
+    #
+    # Ids are a monotically increasing integer which
+    # starts as 1 (a falsy plugin ID is considered unset
+    # in various parts of the codebase).
+    #
+    __id_generator = itertools.count(1)
 
     # Hold on to a lookup table by counter of all instantiated plugins.
     # We use this to send the id back from child processes so we can lookup
@@ -163,7 +167,7 @@ class Plugin():
     # scheduling tasks.
     __TABLE = WeakValueDictionary()
 
-    def __init__(self, name, context, project, provenance, type_tag):
+    def __init__(self, name, context, project, provenance, type_tag, unique_id=None):
 
         self.name = name
         """The plugin name
@@ -184,10 +188,14 @@ class Plugin():
         # to give us a topological sort over all elements.
         # Modifying how we handle ids here will modify the behavior of the
         # Element's state handling.
-        self._unique_id = next(self.__id_generator)
-
-        # register ourself in the table containing all existing plugins
-        self.__TABLE[self._unique_id] = self
+        if unique_id is None:
+            # Register ourself in the table containing all existing plugins
+            self._unique_id = next(self.__id_generator)
+            self.__TABLE[self._unique_id] = self
+        else:
+            # If the unique ID is passed in the constructor, then it is a cloned
+            # plugin in a subprocess and should use the same ID.
+            self._unique_id = unique_id
 
         self.__context = context        # The Context object
         self.__project = project        # The Project object
@@ -656,6 +664,7 @@ class Plugin():
     #
     @classmethod
     def _lookup(cls, unique_id):
+        assert unique_id != 0, "Looking up invalid plugin ID 0, ID counter starts at 1"
         assert unique_id in cls.__TABLE, "Could not find plugin with ID {}".format(unique_id)
         return cls.__TABLE[unique_id]
 
diff --git a/buildstream/source.py b/buildstream/source.py
index b8759c0d8..f72aeae86 100644
--- a/buildstream/source.py
+++ b/buildstream/source.py
@@ -225,10 +225,10 @@ class Source(Plugin):
     __defaults = {}          # The defaults from the project
     __defaults_set = False   # Flag, in case there are not defaults at all
 
-    def __init__(self, context, project, meta, *, alias_override=None):
+    def __init__(self, context, project, meta, *, alias_override=None, unique_id=None):
         provenance = _yaml.node_get_provenance(meta.config)
         super().__init__("{}-{}".format(meta.element_name, meta.element_index),
-                         context, project, provenance, "source")
+                         context, project, provenance, "source", unique_id=unique_id)
 
         self.__element_name = meta.element_name         # The name of the element owning this source
         self.__element_index = meta.element_index       # The index of the source in the owning element's source list
@@ -916,7 +916,9 @@ class Source(Plugin):
         alias = self._get_alias()
         source_kind = type(self)
 
-        clone = source_kind(context, project, self.__meta, alias_override=(alias, uri))
+        clone = source_kind(context, project, self.__meta,
+                            alias_override=(alias, uri),
+                            unique_id=self._unique_id)
 
         # Do the necessary post instantiation routines here
         #