Re: [Discuss-gnuradio] FG probe generation of thread.start() race conditions (python tutorials)

[Martin Braun]

James,

thanks for pointing that out!

On 03/29/2017 10:22 AM, James Shimer wrote:
> Sorry if this is a duplicate/newbie question (didn't find anything
> searching).  When going thru the python examples.  I came across a race
> condition where the thread would start to run prior to object's
> constructor completing.  The fix is to manually move the code generated
> for starting the probe thread to the very end of the constructor.
> 
> 
> If this "bug" is open already thanks for your time, if not here are some
> more details:
> 
> 
> Tutorial 3, section 3.1.5, you're asked to modify the probe thread to
> reference members of the class to set_ampl and set_freq, those functions
> in-turn access members of the object, which may not have been
> initialized yet because the thread runs while the constructor is still
> running.
> 
> https://wiki.gnuradio.org/index.php/Guided_Tutorial_GNU_Radio_in_Python
> 
> The symptom:
> 
> Exception in thread Thread-1:
> 
> Traceback (most recent call last):
> 
>   File
> "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py",
> line 801, in __bootstrap_inner
> 
>     self.run()
> 
>   File
> "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py",
> line 754, in run
> 
>     self.__target(*self.__args, **self.__kwargs)
> 
>   File "power.py", line 95, in _variable_function_probe_0_probe
> 
>     self.set_ampl(0.3)
> 
>   File "power.py", line 174, in set_ampl
> 
>     self.analog_sig_source_x_0.set_amplitude(self.ampl)
> 
>   File
> "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/gnuradio/gr/hier_block2.py",
> line 92, in __getattr__
> 
>     return getattr(self._impl, name)
> 
> AttributeError: 'top_block_sptr' object has no attribute
> 'analog_sig_source_x_0'
> 
> 
> The resolution:
> 
> diff -rupN if_else.py if_else2.py 
> 
> --- if_else.py2017-03-29 13:20:32.000000000 -0400
> 
> +++ if_else2.py2017-03-29 13:19:37.000000000 -0400
> 
> @@ -101,7 +101,6 @@ class if_else(gr.top_block, Qt.QWidget):
> 
>                  time.sleep(1.0 / (10))
> 
>          _variable_function_probe_0_thread =
> threading.Thread(target=_variable_function_probe_0_probe)
> 
>          _variable_function_probe_0_thread.daemon = True
> 
> -        _variable_function_probe_0_thread.start()
> 
>  
> 
>          self.qtgui_time_sink_x_0 = qtgui.time_sink_f(
> 
>          1024, #size
> 
> @@ -160,6 +159,7 @@ class if_else(gr.top_block, Qt.QWidget):
> 
>          self.connect((self.analog_sig_source_x_0, 0),
> (self.blocks_throttle_0, 0))
> 
>          self.connect((self.analog_sig_source_x_1, 0),
> (self.qtgui_time_sink_x_0, 0))
> 
>          self.connect((self.blocks_throttle_0, 0), (self.probe, 0))
> 
> +        _variable_function_probe_0_thread.start()
> 
>  
> 
>      def closeEvent(self, event):
> 
>          self.settings = Qt.QSettings("GNU Radio", "if_else")
> 
> 
> 
> Thanks
> 
> 
> 
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