[vtkusers] VTK memory management

José M. Rodriguez Bacallao jmrbcu at gmail.com
Wed Aug 29 19:42:20 EDT 2012

so, I need to keep using vtk messenger from tvtk?

On Wed, Aug 29, 2012 at 7:14 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> No, the tp_traverse function for PyVTKObject does not traverse the
> object's observers, so observer reference cycles will not be detected
> by the python garbage collector.  This might be fixed in a later
> version of VTK, i.e. VTK six point something (or sooner if someone
> provides a patch).
>  - David
> On Wed, Aug 29, 2012 at 4:28 PM, José M. Rodriguez Bacallao
> <jmrbcu at gmail.com> wrote:
>> with respect to reference cycles, some time ago I was using vtk
>> Messenger from TVTK to get rid of reference cycles when adding
>> observers to any vtk object, this is the reasoning from the source
>> code documentation in this file:
>> """
>> Implements a simple, robust, safe, Messenger class that allows one to
>> register callbacks for a signal/slot (or event/handler) kind of
>> messaging system.  One can basically register a callback
>> function/method to be called when an object sends a particular event.
>> The Messenger class is Borg.  So it is easy to instantiate and use.
>> This module is also reload-safe, so if the module is reloaded the
>> callback information is not lost.  Method callbacks do not have a
>> reference counting problem since weak references are used.
>> The main functionality of this module is provided by three functions,
>> `connect`, `disconnect` and `send`.
>> Here is example usage with VTK::
>>     >>> import messenger, vtk
>>     >>> def cb(obj, evt):
>>     ...  print obj.__class__.__name__, evt
>>     ...
>>     >>> o = vtk.vtkProperty()
>>     >>> o.AddObserver('ModifiedEvent', messenger.send)
>>     1
>>     >>> messenger.connect(o, 'ModifiedEvent', cb)
>>     >>>
>>     >>> o.SetRepresentation(1)
>>     vtkOpenGLProperty ModifiedEvent
>>     >>> messenger.connect(o, 'AnyEvent', cb)
>>     >>> o.SetRepresentation(2)
>>     vtkOpenGLProperty ModifiedEvent
>>     vtkOpenGLProperty ModifiedEvent
>>     >>>
>>     >>> messenger.send(o, 'foo')
>>     vtkOpenGLProperty foo
>>     >>> messenger.disconnect(o, 'AnyEvent')
>>     >>> messenger.send(o, 'foo')
>>     >>>
>> This approach is necessary if you don't want to be bitten by reference
>> cycles.  If you have a Python object holding a reference to a VTK
>> object and pass a method of the object to the AddObserver call, you
>> will get a reference cycle that cannot be collected by the garbage
>> collector.  Using this messenger module gets around the problem.
>> Also note that adding a connection for 'AnyEvent' will trigger a
>> callback no matter what event was generated.  The code above also
>> shows how disconnection works.
>> """
>> right now, has vtk solved this problem?
>> On Wed, Aug 29, 2012 at 4:38 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>> In general python's memory management is fairly deterministic because
>>> it relies on reference counting (i.e. most objects are deleted as soon
>>> as they aren't needed anymore).  But if reference cycles are present,
>>> the behavior can become non-deterministic, because it depends on when
>>> the garbage collector is run.  You can always call gc.collect()
>>> yourself to force the garbage collection to occur at certain times in
>>> your program.
>>>  - David
>>> On Wed, Aug 29, 2012 at 2:03 PM, Thiago Franco Moraes
>>> <tfmoraes at cti.gov.br> wrote:
>>>> Hi,
>>>> I'm doing some tests about memory management in VTK with Python. I
>>>> wrote this little python script [1]. It takes as parameter a filename
>>>> to a vtkPolydata saved in a xml file and do some processings in it. In
>>>> this script I'm taking care of freeing the memory used by each filter
>>>> and intermediate vtkPolydata. I'm using an tool called memory profiler
>>>> (very interesting by the way) [2] to measure the memory used along the
>>>> script execution. The problem is the memory measurement in the end of
>>>> script execution is somewhat strange, because the memory measurement
>>>> is very fluctuating, ranging from 170MB to 500MB. Is this expected?
>>>> I'm freeing memory from vtk objects in the right way? It's a problem
>>>> with Python?
>>>> Thanks!
>>>> [1] - http://pastebin.com/iYUK1jxk
>>>> [2] - https://github.com/fabianp/memory_profiler
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