fail to receive GST_MESSAGE_STATE_CHANGED (GST_STATE_NULL) of pipeline, but all receive the msg for all its children

[Halley Zhao]

Hi experts:
I want to do cleanup after pipeline changed to GST_STATE_NULL. however I
received GST_MESSAGE_STATE_CHANGED with newstate of GST_STATE_NULL of its
children element, but not the pipeline itself.

I don't know whether there is something wrong in my code, or it is by
design?
my pipeline contains "appsrc-->h264parse-->videodecode-->appsink". here is
my log:
the source code sees attachment

(cb_need_data, 148)emit eos signal
(bus_call, 61)End of stream

(bus_call, 84)my_sink state change, old state: PLAYING, new state: PAUSED
(bus_call, 84)my_vdec state change, old state: PLAYING, new state: PAUSED
(bus_call, 84)my_h264parse state change, old state: PLAYING, new state:
PAUSED
(bus_call, 84)my_appsrc state change, old state: PLAYING, new state: PAUSED
(bus_call, 84)my_pipeline state change, old state: PLAYING, new state:
PAUSED
(bus_call, 84)my_sink state change, old state: PAUSED, new state: READY
(bus_call, 84)my_vdec state change, old state: PAUSED, new state: READY
(bus_call, 84)my_h264parse state change, old state: PAUSED, new state: READY
(bus_call, 84)my_appsrc state change, old state: PAUSED, new state: READY
(bus_call, 84)my_pipeline state change, old state: PAUSED, new state: READY
(bus_call, 84)my_sink state change, old state: READY, new state: NULL
(bus_call, 84)my_vdec state change, old state: READY, new state: NULL
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