diff --git a/meshroom/core/desc.py b/meshroom/core/desc.py
index 510df4c1..e5df6d54 100755
--- a/meshroom/core/desc.py
+++ b/meshroom/core/desc.py
@@ -2,6 +2,7 @@ from meshroom.common import BaseObject, Property, Variant
 from enum import Enum  # available by default in python3. For python2: "pip install enum34"
 import collections
 import os
+import psutil
 
 
 class Attribute(BaseObject):
@@ -195,7 +196,52 @@ class Node(object):
     def __init__(self):
         pass
 
+    def stop(self, node):
+        pass
+
+    def process(self, node):
+        raise NotImplementedError('No process implementation on this node')
+
 
 class CommandLineNode(Node):
     """
     """
+
+    def buildCommandLine(self, node):
+        cmdPrefix = ''
+        if 'REZ_ENV' in os.environ:
+            cmdPrefix = '{rez} {packageFullName} -- '.format(rez=os.environ.get('REZ_ENV'), packageFullName=node.packageFullName)
+        return cmdPrefix + node.nodeDesc.commandLine.format(**node._cmdVars)
+
+    def stop(self, node):
+        if node.subprocess:
+            node.subprocess.terminate()
+
+    def process(self, node):
+        try:
+            with open(node.logFile(), 'w') as logF:
+                cmd = self.buildCommandLine(node)
+                print(' - commandLine:', cmd)
+                print(' - logFile:', node.logFile())
+                node.subprocess = psutil.Popen(cmd, stdout=logF, stderr=logF, shell=True)
+
+                # store process static info into the status file
+                node.status.commandLine = cmd
+                # node.status.env = node.proc.environ()
+                # node.status.createTime = node.proc.create_time()
+
+                node.statThread.proc = node.subprocess
+                stdout, stderr = node.subprocess.communicate()
+                node.subprocess.wait()
+
+                node.status.returnCode = node.subprocess.returncode
+
+            if node.subprocess.returncode != 0:
+                with open(node.logFile(), 'r') as logF:
+                    logContent = ''.join(logF.readlines())
+                raise RuntimeError('Error on node "{}":\nLog:\n{}'.format(node.name, logContent))
+        except:
+            raise
+        finally:
+            node.subprocess = None
+
diff --git a/meshroom/core/graph.py b/meshroom/core/graph.py
index 92e8fc30..6edd378d 100644
--- a/meshroom/core/graph.py
+++ b/meshroom/core/graph.py
@@ -51,6 +51,9 @@ else:
 
 stringIsLinkRe = re.compile('^\{.+\}$')
 
+def isCollection(v):
+    return isinstance(v, collections.Iterable) and not isinstance(v, basestring)
+
 @contextmanager
 def GraphModification(graph):
     """
@@ -510,6 +513,7 @@ class Node(BaseObject):
     def updateInternals(self):
         self._cmdVars = {
             'cache': self.graph.cacheDir,
+            'nodeType': self.nodeType,
         }
         for uidIndex, associatedAttributes in self.attributesPerUid.items():
             assAttr = [(a.getName(), a.uid(uidIndex)) for a in associatedAttributes]
@@ -541,10 +545,8 @@ class Node(BaseObject):
             if attr.isInput:
                 continue  # skip inputs
             attr.value = attr.attributeDesc.value.format(
-                nodeType=self.nodeType,
                 **self._cmdVars)
             attr._invalidationValue = attr.attributeDesc.value.format(
-                nodeType=self.nodeType,
                 **cmdVarsNoCache)
             v = attr.value
 
@@ -559,13 +561,7 @@ class Node(BaseObject):
 
     @property
     def internalFolder(self):
-        return self.nodeDesc.internalFolder.format(nodeType=self.nodeType, **self._cmdVars)
-
-    def commandLine(self):
-        cmdPrefix = ''
-        if 'REZ_ENV' in os.environ:
-            cmdPrefix = '{rez} {packageFullName} -- '.format(rez=os.environ.get('REZ_ENV'), packageFullName=self.packageFullName)
-        return cmdPrefix + self.nodeDesc.commandLine.format(nodeType=self.nodeType, **self._cmdVars)
+        return self.nodeDesc.internalFolder.format(**self._cmdVars)
 
     def statusFile(self):
         return os.path.join(self.graph.cacheDir, self.internalFolder, 'status')
@@ -648,48 +644,26 @@ class Node(BaseObject):
         self.upgradeStatusTo(Status.SUBMITTED_LOCAL)
 
     def stopProcess(self):
-        if self._subprocess:
-            self._subprocess.terminate()
+        self.nodeDesc.stop(self)
 
     def process(self):
         global runningProcesses
         runningProcesses[self.name] = self
         self.upgradeStatusTo(Status.RUNNING)
-        statThread = stats.StatisticsThread(self)
-        statThread.start()
+        self.statThread = stats.StatisticsThread(self)
+        self.statThread.start()
         startTime = time.time()
         try:
-            with open(self.logFile(), 'w') as logF:
-                cmd = self.commandLine()
-                print(' - commandLine:', cmd)
-                print(' - logFile:', self.logFile())
-                self._subprocess = psutil.Popen(cmd, stdout=logF, stderr=logF, shell=True)
-
-                # store process static info into the status file
-                self.status.commandLine = cmd
-                # self.status.env = self.proc.environ()
-                # self.status.createTime = self.proc.create_time()
-
-                statThread.proc = self._subprocess
-                stdout, stderr = self._subprocess.communicate()
-                self._subprocess.wait()
-
-                self.status.returnCode = self._subprocess.returncode
-
-            if self._subprocess.returncode != 0:
-                with open(self.logFile(), 'r') as logF:
-                    logContent = ''.join(logF.readlines())
-                raise RuntimeError('Error on node "{}":\nLog:\n{}'.format(self.name, logContent))
+            self.nodeDesc.process(self)
         except BaseException:
             self.upgradeStatusTo(Status.ERROR)
             raise
         finally:
             elapsedTime = time.time() - startTime
             print(' - elapsed time:', elapsedTime)
-            self._subprocess = None
             # ask and wait for the stats thread to stop
-            statThread.stopRequest()
-            statThread.join()
+            self.statThread.stopRequest()
+            self.statThread.join()
             del runningProcesses[self.name]
 
         self.upgradeStatusTo(Status.SUCCESS)
diff --git a/meshroom/core/stats.py b/meshroom/core/stats.py
index 6d988cd2..d9ef5e38 100644
--- a/meshroom/core/stats.py
+++ b/meshroom/core/stats.py
@@ -190,7 +190,7 @@ class StatisticsThread(threading.Thread):
     def __init__(self, node):
         threading.Thread.__init__(self)
         self.node = node
-        self.proc = None
+        self.proc = psutil.Process()  # by default current process pid
         self.statistics = self.node.statistics
         self._stopFlag = threading.Event()