plugin.py: Allow passing a unique_id through the constructor.

In the case of cloned Sources, they should not be allocating
a new ID in track() and fetch() in case they do communicate their
ID back to the main process, they should inherit the same ID of
the Source they were cloned from.

1 files changed, 9 insertions, 5 deletions

diff --git a/buildstream/plugin.py b/buildstream/plugin.py
index 307aefa69..fbcf249bb 100644
--- a/buildstream/plugin.py
+++ b/buildstream/plugin.py
@@ -167,7 +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
@@ -188,10 +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