From 115b0cf07ae1c28f143171e610785da1421fc37f Mon Sep 17 00:00:00 2001
From: wyzula-jan <jan.wyzula@psi.ch>
Date: Mon, 3 Aug 2026 11:26:41 +0200
Subject: [PATCH] fix(connector): break C++-anchored reference cycle retaining
 task owners

---
 bec_widgets/utils/bec_connector.py     | 12 +++++++++++-
 tests/unit_tests/test_bec_connector.py | 23 +++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/bec_widgets/utils/bec_connector.py b/bec_widgets/utils/bec_connector.py
index e4f71bc1..511a5edc 100644
--- a/bec_widgets/utils/bec_connector.py
+++ b/bec_widgets/utils/bec_connector.py
@@ -403,8 +403,18 @@ class BECConnector:
         # Keep a reference to the worker so it is not garbage collected.
         self._workers.append(worker)
 
-        # When the worker is done (success or failure), remove it from our list.
+        # When the worker is done (success or failure), remove it from our
+        # list. The closure must disconnect itself from both signals before
+        # returning: the Qt connection holds the closure strongly from C++,
+        # and the closure captures self and worker — without the disconnect
+        # this forms a reference cycle anchored in C++ that Python's GC
+        # cannot break, keeping the owning widget alive forever.
         def _discard_worker(*_):
+            for signal in (worker.signals.completed, worker.signals.failed):
+                try:
+                    signal.disconnect(_discard_worker)
+                except (RuntimeError, TypeError):
+                    pass
             try:
                 self._workers.remove(worker)
             except ValueError:
diff --git a/tests/unit_tests/test_bec_connector.py b/tests/unit_tests/test_bec_connector.py
index 8dd77952..5b4fe749 100644
--- a/tests/unit_tests/test_bec_connector.py
+++ b/tests/unit_tests/test_bec_connector.py
@@ -277,3 +277,26 @@ def test_bec_connector_parent_id_returns_none_on_error(bec_connector):
         bec_connector, "_get_rpc_parent_ancestor", side_effect=ValueError("broken hierarchy")
     ):
         assert bec_connector.parent_id is None
+
+
+def test_bec_connector_worker_completion_does_not_retain_owner(qtbot, mocked_client):
+    """The worker-discard closure is held strongly
+    by the Qt signal connection and captures the owner; without disconnecting
+    itself it forms a C++-anchored reference cycle that keeps the owner (and
+    widget) alive forever."""
+    import gc
+    import weakref
+
+    connector = _CleanupBroadcastWidget(client=mocked_client)
+    connector.submit_task(lambda: None)
+    qtbot.waitUntil(lambda: not connector._workers, timeout=5000)
+
+    ref = weakref.ref(connector)
+    connector.close()
+    connector.deleteLater()
+    qtbot.wait(20)
+    del connector
+    for _ in range(3):
+        gc.collect()
+
+    assert ref() is None, "connector kept alive by worker completion closure"