[core] add GraphVisitMessage exceptions mecanism

allow to stop branch or graph visit by throwing specific exceptions in visitor callbacks

meshroom/core/exception.py

@@ -28,3 +28,18 @@ class NodeUpgradeError(GraphException):
         if details:
             msg += ": {}".format(details)
         super(NodeUpgradeError, self).__init__(msg)
+
+
+class GraphVisitMessage(GraphException):
+    """ Base class for sending messages via exceptions during a graph visit. """
+    pass
+
+
+class StopGraphVisit(GraphVisitMessage):
+    """ Immediately interrupt graph visit. """
+    pass
+
+
+class StopBranchVisit(GraphVisitMessage):
+    """ Immediately stop branch visit. """
+    pass

meshroom/core/graph.py

@@ -14,7 +14,7 @@ import meshroom
 import meshroom.core
 from meshroom.common import BaseObject, DictModel, Slot, Signal, Property
 from meshroom.core.attribute import Attribute, ListAttribute
-from meshroom.core.exception import UnknownNodeTypeError
+from meshroom.core.exception import StopGraphVisit, StopBranchVisit
 from meshroom.core.node import node_factory, Status, Node, CompatibilityNode
 
 # Replace default encoder to support Enums
@@ -586,10 +586,19 @@ class Graph(BaseObject):
             assert not self.dirtyTopology
             nodes = sorted(nodes, key=lambda item: item.depth)
 
+        try:
             for node in nodes:
                 self.dfsVisit(node, visitor, colors, nodeChildren, longestPathFirst)
+        except StopGraphVisit:
+            pass
 
     def dfsVisit(self, u, visitor, colors, nodeChildren, longestPathFirst):
+        try:
+            self._dfsVisit(u, visitor, colors, nodeChildren, longestPathFirst)
+        except StopBranchVisit:
+            pass
+
+    def _dfsVisit(self, u, visitor, colors, nodeChildren, longestPathFirst):
         colors[u] = GRAY
         visitor.discoverVertex(u, self)
         # d_time[u] = time = time + 1