Taken from 2.4/HEAD:

- Bug #875692: Improve signal handling, especially when using threads, by
  forcing an early re-execution of PyEval_EvalFrame() "periodic" code when
  things_to_do is not cleared by Py_MakePendingCalls().

Misc/NEWS

@@ -36,6 +36,10 @@ Core and builtins
 
 - Bug #845802: Python crashed when __init__.py is a directory.
 
+- Bug #875692: Improve signal handling, especially when using threads, by
+  forcing an early re-execution of PyEval_EvalFrame() "periodic" code when
+  things_to_do is not cleared by Py_MakePendingCalls().
+
 Extension modules
 -----------------
 

Python/ceval.c

@@ -785,6 +785,12 @@ eval_frame(PyFrameObject *f)
 					why = WHY_EXCEPTION;
 					goto on_error;
 				}
+				if (things_to_do)
+					/* MakePendingCalls() didn't succeed.
+					   Force early re-execution of this
+					   "periodic" code, possibly after
+					   a thread switch */
+					_Py_Ticker = 0;
 			}
 #if !defined(HAVE_SIGNAL_H) || defined(macintosh)
 			/* If we have true signals, the signal handler