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Trouble with ros and cython (update)

asked 2016-06-02 04:17:49 -0500

Sietse gravatar image

updated 2016-06-03 05:36:46 -0500

Hello list,

I really am struggling with using ROS (Indigo on Ubuntu 14.04) and some code that uses Cython (version 0.20.1post0) to bind a C-library to python. In an earlier attempt I used swig, but I also failed in getting that to work reliably.

If I use the code generated with Cython in python without using anything from ROS, everything is fine, no errors or crashes.

But as soon as I use ROS, even only something like 'rospy.init_node('nodename')', there are occasional crashes or hangs. Say something like every 10-th start of that program.

I also fiddled with signal catching of e.g. signal.SIGSEGV, which work when I send it when the program is running, but is not working when a sigsegv really happens (I think).

Does anyone know is there are some clever tricks done in ROS (of Cython) that could explain this? Or a pointer how to attack this? I really am at a loss here.

UPDATE:

I found that the crashes almost always occur in the sleep function of rospy.Rate. I find it strange that initially calling some (Cython) function make this sleep function crash.

Here a stripped version of the program that still has the crashes.

rospy.init_node('peratestinit')

RTM2v_Init()
for DevNr in range(4):
    rtm_usb_ReadStdMsg(DevNr)
    rtm_usb_Read_ready(DevNr)
    rtm_usb_SendStdMsg(DevNr,0, 0, 0, 0);

rate = 50
r = rospy.Rate(rate)

k = 0 ;running = True
while running == True:
    # do some (control) stuff, including some (Cython) rtm_usb function calls
    j = 0
    for i in range(1000):
        j += math.sin(i)
    print 'insleep', j
    r.sleep()
    print 'uitsleep'
    k = k+1
    if k == 10:
        running = False

The rtm functions are communication with a robot arm using Cython generated code. The last printout almost always is the print from direcly before the r.sleep().

If I remove the rospy.init_node and use the regular python time.sleep() instead of r.sleep(), so no ROS at all, everything works!

???

Thanks in advance, Sietse

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answered 2016-06-06 08:45:52 -0500

Sietse gravatar image

To answer my own question, I found the error. There was a programming error on the Cython site, and for some reason it only manifested itself when running under ROS.

Thanks for your attention. Sietse

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Thanks for reporting back. Can you say anything about whether that programming error has been fixed, is there a work-around, any more detail?

gvdhoorn gravatar image gvdhoorn  ( 2016-06-06 09:03:15 -0500 )edit

It was an error on my part, not in Cython itself. I used a C-function with a (void *) parameter with which data should be returned in a wrong way.

By the way, I do this to get our PERA (Philips Experimental Robot Arm) under ROS control. There should be such an arm in Delft if I am correct.

Sietse gravatar image Sietse  ( 2016-06-06 13:24:51 -0500 )edit

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Asked: 2016-06-02 04:17:49 -0500

Seen: 265 times

Last updated: Jun 06 '16