(fix): Return a response that arrived instead of reporting a timeout

python/src/xstudio/connection/__init__.py

@@ -401,7 +401,19 @@ def request(self, *args):
     def response(self, req_id, timeout_milli=None):
         """"""
         if timeout_milli is not None:
-            self._dequeue_messages(timeout_milli, req_id)
+            try:
+                self._dequeue_messages(timeout_milli, req_id)
+            except TimeoutError:
+                # _dequeue_messages files every response it dequeues into
+                # self.responses, whatever request it was watching for - only
+                # its break is specific to watch_for. So another consumer of
+                # this connection's queue may have taken our response and
+                # stored it correctly while we were still waiting. Not having
+                # dequeued it ourselves is not the same as no answer arriving,
+                # and callers treat a timeout as evidence an actor is
+                # unresponsive.
+                if self.responses.get(req_id) is None:
+                    raise
 
         return self._response(req_id)
 

python/test/test_connection.py

@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: Apache-2.0
+import pytest
+from xstudio.core import version_atom
+
+
+def test_response_already_received_is_not_a_timeout(spawn):
+    """A response dequeued by another consumer must be returned, not reported
+    as a timeout.
+
+    _dequeue_messages files every response it dequeues into self.responses,
+    whatever request it was watching for - only its break is specific to
+    watch_for. So any other consumer of the queue can pull our response and
+    store it correctly while we are still waiting for it.
+
+    dequeue_messages() here is that other consumer. Calling it on this thread
+    rather than another removes the race without changing the mechanism: it
+    pumps with watch_for unset, so it files the response and carries on instead
+    of breaking on it.
+    """
+    req_id = spawn.request(spawn.remote(), version_atom())
+    spawn.dequeue_messages(300)
+
+    assert spawn.responses[req_id] is not None, "precondition: the answer was recorded"
+    assert spawn.response(req_id, 300) is not None
+
+
+def test_genuine_timeout_still_raises(spawn):
+    """No response was ever recorded for this id, so it must still raise."""
+    unused_req_id = 0x7FFFFFF0
+    assert unused_req_id not in spawn.responses
+
+    with pytest.raises(TimeoutError):
+        spawn.response(unused_req_id, 300)