scheduler.py: Call is_fork_allowed() right before spawning jobs

gRPC channels might be opened after the scheduler has already been
started. Make sure channels are closed right before spawning jobs.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/buildstream/_scheduler/scheduler.py b/src/buildstream/_scheduler/scheduler.py
index 6133cbfd7..08db1a1e9 100644
--- a/src/buildstream/_scheduler/scheduler.py
+++ b/src/buildstream/_scheduler/scheduler.py
@@ -165,8 +165,6 @@ class Scheduler():
     #
     def run(self, queues, casd_process):
 
-        assert self.context.is_fork_allowed()
-
         # Hold on to the queues to process
         self.queues = queues
 
@@ -408,6 +406,13 @@ class Scheduler():
             # If that happens, do another round.
             process_queues = any(q.dequeue_ready() for q in self.queues)
 
+        # Check whether fork is allowed before starting jobs
+        if not self.context.is_fork_allowed():
+            message = Message(MessageType.BUG, "Fork is not allowed", detail="Background threads are active")
+            self._notify(Notification(NotificationType.MESSAGE, message=message))
+            self.terminate_jobs()
+            return
+
         # Start the jobs
         #
         for job in ready: