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Segfault when using callbacks in gst-python for buffer retrieval

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Matthias Blaicher
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Segfault when using callbacks in gst-python for buffer retrieval

Matthias Blaicher
Hallo together,

I'm working on a project which requires me to to buffer frames from a
video4linux source in Python. I decided that gstreamer is perfectly
fit for such a task and have already tried some initial code - Which
all fail in a non spectacular segfault.

Here is what I'm trying to do:

I have such a path:
v4lsrc ! video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace !
pngenc snapshot=False  ! fakesink name=sink

Which should generate a continuous stream of png frames. Now i try to
intercept the exchanged Buffer objects by using the handoff event of
fakesink with a callback.  But whenever I activate the callback, the
python interpreter dies with a segmentation fault.  I also tried to
intercept the Buffers with the Pad.add_buffer_probe call, but that
fails the same way.

My code is:

import gst
import time

gst.debug_set_active(True)
gst.debug_set_default_threshold(4)


def callback(fakesink, buffer, pad, data=None):
   return True


def probe_callback_fakesrc(pad, buffer):
   return True

#v4lsrc
pipeline = gst.parse_launch('videotestsrc !
video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace ! pngenc
snapshot=False  ! fakesink name=sink')
fakesink = pipeline.get_by_name('sink')

# Way 1
fakesink.props.signal_handoffs = True
fakesink.connect("handoff", callback)

## Way 2
#pad = fakesink.get_pad('sink')
#pad.add_buffer_probe(probe_callback_fakesrc)

pipeline.set_state(gst.STATE_PLAYING)

while True:
   #Sleep so that context switching for gst works
   time.sleep(1)



Which fails such as (with debug leve 4 and strace)

0:00:04.553704144  9029 0x832f1d8 INFO            GST_STATES
gstelement.c:2148:gst_element_continue_state:<sink> completed state
change to PLAYING
0:00:04.553717205  9029 0x832f1d8 INFO            GST_STATES
gstelement.c:2161:gst_element_continue_state:<sink> posting
state-changed PAUSED to PLAYING
0:00:04.553714760  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1508:gst_base_sink_wait_preroll:<sink> continue after
preroll
0:00:04.553743117  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1678:gst_base_sink_do_sync:<sink> possibly waiting for
clock to reach 0:00:00.000000000
0:00:04.553763652  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1468:gst_base_sink_wait_clock:<sink> sync disabled
0:00:04.553784466  9029 0x8325750 DEBUG             basesink
gstbasesink.c:1684:gst_base_sink_do_sync:<sink> clock returned 4
0:00:04.553798993  9029 0x8325750 DEBUG             basesink
gstbasesink.c:2029:gst_base_sink_render_object:<sink> rendering buffer
0x8328e68
0:00:04.553789634  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:337:gst_bus_post:<bus0> [msg 0x83321d0] posting on bus, type
state-changed, GstMessageState, old-state=(GstState)GST_STATE_PAUSED,
new-state=(GstState)GST_STATE_PLAYING,
pending-state=(GstState)GST_STATE_VOID_PENDING; from source <sink>
0:00:04.553835034  9029 0x832f1d8 DEBUG                  bin
gstbin.c:2719:gst_bin_handle_message_func:<pipeline0> [msg 0x83321d0]
handling child sink message of type state-changed
0:00:04.553848933  9029 0x832f1d8 DEBUG                  bin
gstbin.c:2923:gst_bin_handle_message_func:<pipeline0> posting message
upward
0:00:04.553862133  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:337:gst_bus_post:<bus1> [msg 0x83321d0] posting on bus, type
state-changed, GstMessageState, old-state=(GstState)GST_STATE_PAUSED,
new-state=(GstState)GST_STATE_PLAYING,
pending-state=(GstState)GST_STATE_VOID_PENDING; from source <sink>
0:00:04.553889303  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:367:gst_bus_post:<bus1> [msg 0x83321d0] pushing on async
queue
0:00:04.553887906  9029 0x8325750 DEBUG                pygst
pygstminiobject.c:152:pygstminiobject_new: have to create wrapper for
object 0x8328e68
0:00:04.553904041  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:372:gst_bus_post:<bus1> [msg 0x83321d0] pushed on async queue
0:00:04.553913679  9029 0x8325750 DEBUG                pygst
pygstminiobject.c:171:pygstminiobject_new: created Python object
0xb7ddc800 for GstMiniObject 0x8328e68 [ref:4]
0:00:04.553917870  9029 0x832f1d8 DEBUG              GST_BUS
gstbus.c:363:gst_bus_post:<bus0> [msg 0x83321d0] dropped
0:00:04.553937357  9029 0x832f1d8 DEBUG           GST_STATES
gstelement.c:2380:gst_element_set_state_func:<sink> returned SUCCESS
)     = ? ERESTARTNOHAND (To be restarted)
+++ killed by SIGSEGV +++
Process 9029 detached

I use Ubuntu Hardy with gst.version() == (0, 10, 18, 0)

Does  anybody know what I'm doing wrong here?

Sincerely,

Matthias Blaicher

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Edward Hervey
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Re: Segfault when using callbacks in gst-python for buffer retrieval

Edward Hervey
Administrator
Hi,

  Make your file begin as such:
=============
import gobject
gobject.threads_init()
import gst
...
=============

  That should solve your issues

   Edward

On Fri, 2008-08-29 at 15:01 +0200, Matthias Blaicher wrote:

> Hallo together,
>
> I'm working on a project which requires me to to buffer frames from a
> video4linux source in Python. I decided that gstreamer is perfectly
> fit for such a task and have already tried some initial code - Which
> all fail in a non spectacular segfault.
>
> Here is what I'm trying to do:
>
> I have such a path:
> v4lsrc ! video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace !
> pngenc snapshot=False  ! fakesink name=sink
>
> Which should generate a continuous stream of png frames. Now i try to
> intercept the exchanged Buffer objects by using the handoff event of
> fakesink with a callback.  But whenever I activate the callback, the
> python interpreter dies with a segmentation fault.  I also tried to
> intercept the Buffers with the Pad.add_buffer_probe call, but that
> fails the same way.
>
> My code is:
>
> import gst
> import time
>
> gst.debug_set_active(True)
> gst.debug_set_default_threshold(4)
>
>
> def callback(fakesink, buffer, pad, data=None):
>    return True
>
>
> def probe_callback_fakesrc(pad, buffer):
>    return True
>
> #v4lsrc
> pipeline = gst.parse_launch('videotestsrc !
> video/x-raw-yuv,width=640,height=480 ! ffmpegcolorspace ! pngenc
> snapshot=False  ! fakesink name=sink')
> fakesink = pipeline.get_by_name('sink')
>
> # Way 1
> fakesink.props.signal_handoffs = True
> fakesink.connect("handoff", callback)
>
> ## Way 2
> #pad = fakesink.get_pad('sink')
> #pad.add_buffer_probe(probe_callback_fakesrc)
>
> pipeline.set_state(gst.STATE_PLAYING)
>
> while True:
>    #Sleep so that context switching for gst works
>    time.sleep(1)
>
>
>
> Which fails such as (with debug leve 4 and strace)
>
> 0:00:04.553704144  9029 0x832f1d8 INFO            GST_STATES
> gstelement.c:2148:gst_element_continue_state:<sink> completed state
> change to PLAYING
> 0:00:04.553717205  9029 0x832f1d8 INFO            GST_STATES
> gstelement.c:2161:gst_element_continue_state:<sink> posting
> state-changed PAUSED to PLAYING
> 0:00:04.553714760  9029 0x8325750 DEBUG             basesink
> gstbasesink.c:1508:gst_base_sink_wait_preroll:<sink> continue after
> preroll
> 0:00:04.553743117  9029 0x8325750 DEBUG             basesink
> gstbasesink.c:1678:gst_base_sink_do_sync:<sink> possibly waiting for
> clock to reach 0:00:00.000000000
> 0:00:04.553763652  9029 0x8325750 DEBUG             basesink
> gstbasesink.c:1468:gst_base_sink_wait_clock:<sink> sync disabled
> 0:00:04.553784466  9029 0x8325750 DEBUG             basesink
> gstbasesink.c:1684:gst_base_sink_do_sync:<sink> clock returned 4
> 0:00:04.553798993  9029 0x8325750 DEBUG             basesink
> gstbasesink.c:2029:gst_base_sink_render_object:<sink> rendering buffer
> 0x8328e68
> 0:00:04.553789634  9029 0x832f1d8 DEBUG              GST_BUS
> gstbus.c:337:gst_bus_post:<bus0> [msg 0x83321d0] posting on bus, type
> state-changed, GstMessageState, old-state=(GstState)GST_STATE_PAUSED,
> new-state=(GstState)GST_STATE_PLAYING,
> pending-state=(GstState)GST_STATE_VOID_PENDING; from source <sink>
> 0:00:04.553835034  9029 0x832f1d8 DEBUG                  bin
> gstbin.c:2719:gst_bin_handle_message_func:<pipeline0> [msg 0x83321d0]
> handling child sink message of type state-changed
> 0:00:04.553848933  9029 0x832f1d8 DEBUG                  bin
> gstbin.c:2923:gst_bin_handle_message_func:<pipeline0> posting message
> upward
> 0:00:04.553862133  9029 0x832f1d8 DEBUG              GST_BUS
> gstbus.c:337:gst_bus_post:<bus1> [msg 0x83321d0] posting on bus, type
> state-changed, GstMessageState, old-state=(GstState)GST_STATE_PAUSED,
> new-state=(GstState)GST_STATE_PLAYING,
> pending-state=(GstState)GST_STATE_VOID_PENDING; from source <sink>
> 0:00:04.553889303  9029 0x832f1d8 DEBUG              GST_BUS
> gstbus.c:367:gst_bus_post:<bus1> [msg 0x83321d0] pushing on async
> queue
> 0:00:04.553887906  9029 0x8325750 DEBUG                pygst
> pygstminiobject.c:152:pygstminiobject_new: have to create wrapper for
> object 0x8328e68
> 0:00:04.553904041  9029 0x832f1d8 DEBUG              GST_BUS
> gstbus.c:372:gst_bus_post:<bus1> [msg 0x83321d0] pushed on async queue
> 0:00:04.553913679  9029 0x8325750 DEBUG                pygst
> pygstminiobject.c:171:pygstminiobject_new: created Python object
> 0xb7ddc800 for GstMiniObject 0x8328e68 [ref:4]
> 0:00:04.553917870  9029 0x832f1d8 DEBUG              GST_BUS
> gstbus.c:363:gst_bus_post:<bus0> [msg 0x83321d0] dropped
> 0:00:04.553937357  9029 0x832f1d8 DEBUG           GST_STATES
> gstelement.c:2380:gst_element_set_state_func:<sink> returned SUCCESS
> )     = ? ERESTARTNOHAND (To be restarted)
> +++ killed by SIGSEGV +++
> Process 9029 detached
>
> I use Ubuntu Hardy with gst.version() == (0, 10, 18, 0)
>
> Does  anybody know what I'm doing wrong here?
>
> Sincerely,
>
> Matthias Blaicher
>
> -------------------------------------------------------------------------
> This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
> Build the coolest Linux based applications with Moblin SDK & win great prizes
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