Merge branch 'tristan/fix-cloned-plugin-ids' into 'master'

Fix cloned plugin ids

Closes #1012

See merge request BuildStream/buildstream!1316

2 files changed, 21 insertions, 10 deletions

diff --git a/buildstream/plugin.py b/buildstream/plugin.py
index 5fdcdaeb8..d8b6a7359 100644
--- a/buildstream/plugin.py
+++ b/buildstream/plugin.py
@@ -187,8 +187,12 @@ 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
@@ -201,7 +205,7 @@ 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
@@ -222,10 +226,14 @@ 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
@@ -756,6 +764,7 @@ class Plugin():
     #
     @classmethod
     def _lookup(cls, unique_id):
+        assert unique_id != 0, "Looking up invalid plugin ID 0, ID counter starts at 1"
         try:
             return cls.__TABLE[unique_id]
         except KeyError:
diff --git a/buildstream/source.py b/buildstream/source.py
index 6f4ff575b..daf2cb27c 100644
--- a/buildstream/source.py
+++ b/buildstream/source.py
@@ -286,10 +286,10 @@ class Source(Plugin):
     *Since: 1.4*
     """
 
-    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.__source_cache = context.sourcecache
 
@@ -1092,7 +1092,9 @@ class Source(Plugin):
 
         meta.first_pass = self.__first_pass
 
-        clone = source_kind(context, project, meta, alias_override=(alias, uri))
+        clone = source_kind(context, project, meta,
+                            alias_override=(alias, uri),
+                            unique_id=self._unique_id)
 
         # Do the necessary post instantiation routines here
         #