status: do not create thread to run callbacks if timeout is None

ophyd/status.py

@@ -114,10 +114,13 @@ def __init__(self, *, timeout=None, settle_time=0, done=None, success=None):
                 DeprecationWarning,
             )
 
-        self._callback_thread = threading.Thread(
-            target=self._run_callbacks, daemon=True, name=self._tname
-        )
-        self._callback_thread.start()
+        if timeout is None:
+            self._callback_thread = None
+        else:
+            self._callback_thread = threading.Thread(
+                target=self._run_callbacks, daemon=True, name=self._tname
+            )
+            self._callback_thread.start()
 
         if done:
             if success:
@@ -326,6 +329,9 @@ def set_exception(self, exc):
             self._exception = exc
             self._settled_event.set()
 
+        if self._callback_thread is None:
+            self._run_callbacks()
+
     def set_finished(self):
         """
         Mark as finished successfully.
@@ -344,10 +350,21 @@ def set_finished(self):
         # same thread. This just sets an Event, either from this thread (the
         # one calling set_finished) or the thread created below.
         if self.settle_time > 0:
-            threading.Timer(self.settle_time, self._settled_event.set).start()
+            if self._callback_thread is None:
+
+                def settle_done():
+                    self._settled_event.set()
+                    self._run_callbacks()
+
+                threading.Timer(self.settle_time, settle_done).start()
+            else:
+                threading.Timer(self.settle_time, self._settled_event.set).start()
         else:
             self._settled_event.set()
 
+            if self._callback_thread is None:
+                self._run_callbacks()
+
     def _finished(self, success=True, **kwargs):
         """
         Inform the status object that it is done and if it succeeded.

ophyd/tests/test_status.py

@@ -445,6 +445,27 @@ def test_status_timeout_with_settle_time():
         st.wait(2)
 
 
+def test_status_timeout_infinite_with_settle_time():
+    """
+    A StatusTimeoutError is raised when the timeout set in __init__ plus the
+    settle_time has expired.
+    """
+    cb = Mock()
+    st = StatusBase(settle_time=1)
+    st.add_callback(cb)
+
+    # there is no timeout, explicitely set finished ;
+    # the callback should be called after "settle_time"
+    st.set_finished()
+
+    assert cb.call_count == 0
+    with pytest.raises(WaitTimeoutError):
+        # not ready yet
+        st.wait(0.5)
+    st.wait(0.6)
+    cb.assert_called_once()
+
+
 def test_external_timeout():
     """
     A TimeoutError is raised, not StatusTimeoutError or WaitTimeoutError,