_scheduler/scheduler.py: Enforce SafeChildWatcher

In Python 3.8, `ThreadedChildWatcher` is the default watcher that causes
issues with our scheduler. Enforce use of `SafeChildWatcher`.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/buildstream/_scheduler/scheduler.py b/src/buildstream/_scheduler/scheduler.py
index a45da82f9..ca7e9279c 100644
--- a/src/buildstream/_scheduler/scheduler.py
+++ b/src/buildstream/_scheduler/scheduler.py
@@ -171,6 +171,12 @@ class Scheduler:
         # Hold on to the queues to process
         self.queues = queues
 
+        # NOTE: Enforce use of `SafeChildWatcher` as we generally don't want
+        # background threads.
+        # In Python 3.8+, `ThreadedChildWatcher` is the default watcher, and
+        # not `SafeChildWatcher`.
+        asyncio.set_child_watcher(asyncio.SafeChildWatcher())
+
         # Ensure that we have a fresh new event loop, in case we want
         # to run another test in this thread.
         self.loop = asyncio.new_event_loop()