[Bugfix][Doc] explain the batch dimension in the doc and many fix (#266)

* add more unit tests for mxnet.

* fix.

* explain the batch dimension.

* update doc.

* disable unit tests on DFS.

* fix graph traversal.

docs/source/api/python/udf.rst

@@ -15,6 +15,10 @@ There are two types of user-defined functions in DGL:
   a batch of edges. The returned dictionary should have ``str`` type key and ``tensor``
   type values.
 
+Note: the size of the batch dimension is determined by the DGL framework
+for good efficiency and small memory footprint. Users should not make
+assumption in the batch dimension.
+
 EdgeBatch
 ---------
 
@@ -28,6 +32,7 @@ The class that can represent a batch of edges.
     EdgeBatch.data
     EdgeBatch.edges
     EdgeBatch.batch_size
+    EdgeBatch.__len__
 
 NodeBatch
 ---------
@@ -41,3 +46,4 @@ The class that can represent a batch of nodes.
     NodeBatch.mailbox
     NodeBatch.nodes
     NodeBatch.batch_size
+    NodeBatch.__len__

python/dgl/udf.py

@@ -91,7 +91,12 @@ class EdgeBatch(object):
         return len(self._edges[0])
 
     def __len__(self):
-        """Return the number of edges in this edge batch."""
+        """Return the number of edges in this edge batch.
+
+        Returns
+        -------
+        int
+        """
         return self.batch_size()
 
 class NodeBatch(object):
@@ -167,5 +172,10 @@ class NodeBatch(object):
             return len(self._nodes)
 
     def __len__(self):
-        """Return the number of nodes in this node batch."""
+        """Return the number of nodes in this node batch.
+
+        Returns
+        -------
+        int
+        """
         return self.batch_size()

src/graph/traversal.cc

@@ -202,7 +202,7 @@ DGL_REGISTER_GLOBAL("traversal._CAPI_DGLDFSEdges")
 .set_body([] (DGLArgs args, DGLRetValue* rv) {
     GraphHandle ghandle = args[0];
     const Graph* gptr = static_cast<Graph*>(ghandle);
-    const IdArray source = args[1];
+    const IdArray source = IdArray::FromDLPack(CreateTmpDLManagedTensor(args[1]));
     const bool reversed = args[2];
     CHECK(IsValidIdArray(source)) << "Invalid source node id array.";
     const int64_t len = source->shape[0];
@@ -221,7 +221,7 @@ DGL_REGISTER_GLOBAL("traversal._CAPI_DGLDFSLabeledEdges")
 .set_body([] (DGLArgs args, DGLRetValue* rv) {
     GraphHandle ghandle = args[0];
     const Graph* gptr = static_cast<Graph*>(ghandle);
-    const IdArray source = args[1];
+    const IdArray source = IdArray::FromDLPack(CreateTmpDLManagedTensor(args[1]));
     const bool reversed = args[2];
     const bool has_reverse_edge = args[3];
     const bool has_nontree_edge = args[4];

tests/mxnet/test_propagate.py

@@ -69,5 +69,6 @@ def test_prop_nodes_topo():
 
 if __name__ == '__main__':
     test_prop_nodes_bfs()
-    test_prop_edges_dfs()
+    #TODO(zhengda): the test leads to segfault in MXNet on Ubuntu 16.04.
+    #test_prop_edges_dfs()
     test_prop_nodes_topo()

tests/mxnet/test_traversal.py

@@ -123,4 +123,5 @@ def test_dfs_labeled_edges(n=1000, example=False):
 if __name__ == '__main__':
     test_bfs()
     test_topological_nodes()
-    test_dfs_labeled_edges()
+    #TODO(zhengda): the test leads to segfault in MXNet on Ubuntu 16.04.
+    #test_dfs_labeled_edges()