Tf python stuck in wait for transform extrapolation into past/future

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Hi

I am currently publishing msgs out of a bag file, and naturally the time will go backwards everytime I re-run my bagfile. I want my nodes to gracefully restart like RVIZ

Here is my code snippet - inside callback function

   if self.tmap_loaded == True and self.tmap_prop_loaded == True:
        # detection of negative time step
        dt = (rospy.Time.now() - self.last_update_ros_time)
        self.last_update_ros_time = rospy.Time.now()
        if dt.to_sec() < 0:
            print "Negative timestep Clearing tf buffer" 
            self.tf_L.clear()
            time.sleep(10)
            print "Cleared Buffer"
            return
        # generate a pointcloud to represent the UWB FOV mask 
        uwb_mask_pcd = self._gen_pointcloud_uwb_fov(data)
        exception = False
        try:
            # transform points in mask using current tf transform
            self.tf_L.waitForTransform("/map","/body",uwb_mask_pcd.header.stamp,rospy.Dur.(1.0))
            uwb_mask_pcd = self.tf_listener.transformPointCloud("/map", uwb_mask_pcd)
        except (tf.LookupException, tf.ConnectivityException, tf.ExtrapolationException):
            # print str(e)
            exception = True

        if exception == False:
            self._process_uwb_scan(data, uwb_mask_pcd)

Here is the output of the code after the bagfiles stops transmitting (clock stops)

[ERROR] [WallTime: 1396791647.721125] [1354679082.276449] bad callback: <bound method 
    self.tf_listener.waitForTransform("/map",

"/body", uwb_mask_pcd.header.stamp, rospy.Duration(1.0)) Exception: Lookup would require extrapolation into the past. Requested time 1354679074.849999905 but the earliest data is at time 1354679075.295000076, when looking up transform from frame [/body] to frame [/map]

[ERROR] [WallTime: 1396791648.735426] [1354679083.286904] bad callback: <bound method 
    self.tf_listener.waitForTransform("/map",

"/body", uwb_mask_pcd.header.stamp, rospy.Duration(1.0)) Exception: Lookup would require extrapolation into the past. Requested time 1354679074.944000006 but the earliest data is at time 1354679075.295000076, when looking up transform from frame [/body] to frame [/map]

[ERROR] [WallTime: 1396791649.755686] [1354679084.309238] bad callback: <bound method 
    self.tf_listener.waitForTransform("/map",

"/body", uwb_mask_pcd.header.stamp, rospy.Duration(1.0)) Exception: Lookup would require extrapolation into the past. Requested time 1354679075.038000107 but the earliest data is at time 1354679075.295000076, when looking up transform from frame [/body] to frame [/map]

So the bagfile stops publishing clock, yet waitForTransform looks like its stuck, because the error msgs keep popping up. Then I Restart the BagFile

This is the prints I get

Negative timestep Clearing tf buffer then a single unable to look up transforms cache empty and then a bunch of extrapolation into the past errors for waitForTransform. Once print "Cleared Buffer" Occurs I get a bunch of extrapolation into Past and Then Future.... it keeps alternating between them.

I thought waitForTransform is meant to wait only 1 second, but what I think happened is it uses the clock to tell when one second elapsed. I think its trying to wait until the last_time in bag file + 1 second. This time will never come, since I am using sim_time so the clock is controlled by the bag file. Therefore even when I restart the bag file the code is stuck in waitForTransform.

I am using the waitForTransform function to avoid small extrapolations into the future. Is there any way I can fix this? Or Force waitForTransform to exit?