async.TaskThread has a waitUntilIdle method, which causes calling thread to

block until queue is empty. ImageWrapper has method to access TaskThread. This
is primarily used for testing threaded access to ImageWrapper.

fsl/data/imagewrapper.py

@@ -229,6 +229,15 @@ class ImageWrapper(notifier.Notifier):
             self.__taskThraed = None
 
 
+    def getTaskThread(self):
+        """If this ``ImageWrapper`` was created with ``threaded=True``,
+        this method returns the ``TaskThread`` that is used for running
+        data range calculation tasks. Otherwise, this method returns
+        ``False``.
+        """
+        return self.__taskThread
+
+
     def reset(self, dataRange=None):
         """Reset the internal state and known data range of this
         ``ImageWrapper``.
@@ -745,9 +754,9 @@ def isValidFancySliceObj(sliceobj, shape):
     object.
 
     ``nibabel`` refers to slice objects as "fancy" if they comprise anything
-    but tuples of simple ``slice`` objects. The ``ImageWrapper`` class
-    supports one type of "fancy" slicing, where the ``sliceobj`` is a boolean
-    ``numpy`` array of the same shape as the image.
+    but tuples of integers and simple ``slice`` objects. The ``ImageWrapper``
+    class supports one type of "fancy" slicing, where the ``sliceobj`` is a
+    boolean ``numpy`` array of the same shape as the image.
 
     This function returns ``True`` if the given ``sliceobj`` adheres to these
     requirements, ``False`` otherwise.

fsl/utils/async.py

@@ -679,6 +679,12 @@ class TaskThread(threading.Thread):
         self.__stop = True
 
 
+    def waitUntilIdle(self):
+        """Causes the calling thread to block until the task queue is empty.
+        """
+        self.__q.join()
+
+
     def run(self):
         """Run the ``TaskThread``. """
 
@@ -703,6 +709,7 @@ class TaskThread(threading.Thread):
             self.__enqueued.pop(task.name, None)
 
             if not task.enabled:
+                self.__q.task_done()
                 continue
 
             log.debug('Running task: {} [{}]'.format(
@@ -733,6 +740,8 @@ class TaskThread(threading.Thread):
                     type(e).__name__,
                     str(e)),
                     exc_info=True)
+            finally:
+                self.__q.task_done()
 
         self.__q        = None
         self.__enqueued = None