Documentation/4.1/Developers/Tutorials/MemoryManagement - Revision history

UpdateBot: Prepend documentation/versioncheck template. See http://na-mic.org/Mantis/view.php?id=2887

2013-06-14T07:21:23Z

Prepend documentation/versioncheck template. See http://na-mic.org/Mantis/view.php?id=2887

Finetjul at 14:57, 9 October 2012

2012-10-09T14:57:40Z

JChris.FillionR: 4.0 -> 4.1

2012-04-12T04:45:10Z

4.0 -> 4.1

New page

From http://massmail.spl.harvard.edu/public-archives/slicer-devel/2011/007513.html

Like VTK, Slicer contains some "factory" methods:
- vtkMRMLScene::CreateNodeByClass()
- vtkMRMLScene::GetNodesByClass()
- ...
Like in C++, it means that the functions return an object with a reference
count of 1 that nobody "owns" and the caller must take care of releasing
the object to avoid memory leak.

While there is workaround for some methods (
slicer.mrmlScene.CreateNodeByClass('vtkMRMLModelNode') should be replaced
by slicer.vtkMRMLModelNode() ) there is currently no automatic/clean
mechanism to release the object created by such methods.

The only "hack" that exists for now is to decrease the reference count
manually in your code:
nodes = slicer.mrmlScene.GetNodesByClass('vtkMRMLLinearTransformNode')
nodes.SetReferenceCount(1) # ----> (was 2, keep 1 for the python
reference)
...

In C++, the following would apply:
vtkCollection* nodes =
mrmlScene->GetNodesByClass("vtkMRMLLinearTransformNode");
...
nodes->Delete();

or using vtkSmartPointer:
vtkSmartPointer<vtkCollection> nodes;
nodes.TakeReference(mrmlScene->GetNodesByClass("vtkMRMLLinearTransformNode"));
...

Amendment from JC http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=19772

The reference count shouldn't be decreased using the naive approach where
it is set to one. Indeed, internally, the reference count could be any
number greater than one. It doesn't have to be 2.

Considering this last remark, using the following approach is *REQUIRED*,
otherwise it will lead to a CRASH of the application.

n = slicer.mrmlScene.CreateNodeByClass('vtkMRMLViewNode')
slicer.mrmlScene.addNode(n)
n.SetReferenceCount(n.GetReferenceCount() - 1)

Even better, this specific example can be simplified using the following
syntax, this is the *RECOMMENDED* approach, it will prevent bug, memory
leaks and crashes:

n = slicer.mrmlScene.addNode(slicer.vtkMRMLViewNode())

And if the name of the node is generated at runtime, this could be done:

n = eval('slicer.mrmlScene.AddNode(slicer.%s())' % 'vtkMRMLViewNode')

← Older revision		Revision as of 07:21, 14 June 2013
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		+	<noinclude>{{documentation/versioncheck}}</noinclude>
	From http://massmail.spl.harvard.edu/public-archives/slicer-devel/2011/007513.html		From http://massmail.spl.harvard.edu/public-archives/slicer-devel/2011/007513.html

@@ Line 17: / Line 17: @@
 manually in your code:
 nodes = slicer.mrmlScene.GetNodesByClass('vtkMRMLLinearTransformNode')
-nodes.SetReferenceCount(1)      # ----> (was 2, keep 1 for the python
+nodes.UnRegister(slicer.mrmlScene)      # ----> (reference count was 2, keep 1 for the python reference)
 ...
@@ Line 43: / Line 42: @@
   n = slicer.mrmlScene.CreateNodeByClass('vtkMRMLViewNode')
   slicer.mrmlScene.addNode(n)
-  n.SetReferenceCount(n.GetReferenceCount() - 1)
+  n.UnRegister(slicer.mrmlScene)
 Even better, this specific example can be simplified using the following