MS BFS python APIs + EgoNet updates (#1469)

There are various things in this PR.

Multi-Seed (MS) BFS: 
- API tentative 
- Saving research on memory feasability helper function (not in production)
- Saving research on running the current BFS concurrently with streams and threads for analysis perf comparison (not in production)

EgoNet:
- Multithreading in EgoNet which deserializes execution and comes with mild performance improvements on large sizes
- Some cleanup

Authors:
  - Alex Fender (@afender)

Approvers:
  - Chuck Hastings (@ChuckHastings)
  - @Iroy30
  - Brad Rees (@BradReesWork)

URL: #1469

cpp/src/community/egonet.cu

@@ -79,23 +79,26 @@ extract(
 
   // Streams will allocate concurrently later
   std::vector<rmm::device_uvector<vertex_t>> reached{};
-  reached.reserve(handle.get_num_internal_streams());
+  reached.reserve(n_subgraphs);
+  for (vertex_t i = 0; i < n_subgraphs; i++) {
+    // Allocations and operations are attached to the worker stream
+    rmm::device_uvector<vertex_t> local_reach(v, handle.get_internal_stream_view(i));
+    reached.push_back(std::move(local_reach));
+  }
 
   // h_source_vertex[i] is used by other streams in the for loop
   user_stream_view.synchronize();
 #ifdef TIMING
   HighResTimer hr_timer;
   hr_timer.start("ego_neighbors");
 #endif
+
+#pragma omp parallel for
   for (vertex_t i = 0; i < n_subgraphs; i++) {
     // get light handle from worker pool
     raft::handle_t light_handle(handle, i);
     auto worker_stream_view = light_handle.get_stream_view();
 
-    // Allocations and operations are attached to the worker stream
-    rmm::device_uvector<vertex_t> local_reach(v, worker_stream_view);
-    reached.push_back(std::move(local_reach));
-
     // BFS with cutoff
     // consider adding a device API to BFS (ie. accept source on the device)
     rmm::device_uvector<vertex_t> predecessors(v, worker_stream_view);  // not used
@@ -149,10 +152,10 @@ extract(
   neighbors.resize(h_neighbors_offsets[n_subgraphs]);
   user_stream_view.synchronize();
 
-  // Construct the neighboors list concurrently
+// Construct the neighboors list concurrently
+#pragma omp parallel for
   for (vertex_t i = 0; i < n_subgraphs; i++) {
-    raft::handle_t light_handle(handle, i);
-    auto worker_stream_view = light_handle.get_stream_view();
+    auto worker_stream_view = handle.get_internal_stream_view(i);
     thrust::copy(rmm::exec_policy(worker_stream_view),
                  reached[i].begin(),
                  reached[i].end(),

cpp/tests/CMakeLists.txt

@@ -318,6 +318,13 @@ set(MST_TEST_SRC
 
 ConfigureTest(MST_TEST "${MST_TEST_SRC}")
 
+###################################################################################################
+# - Experimental stream tests -----------------------------------------------------
+
+set(EXPERIMENTAL_STREAM_SRCS
+    "${CMAKE_CURRENT_SOURCE_DIR}/experimental/streams.cu")
+
+ConfigureTest(EXPERIMENTAL_STREAM "${EXPERIMENTAL_STREAM_SRCS}" "")
 
 ###################################################################################################
 # - Experimental R-mat graph generation tests -----------------------------------------------------
@@ -375,6 +382,15 @@ set(EXPERIMENTAL_BFS_TEST_SRCS
 
 ConfigureTest(EXPERIMENTAL_BFS_TEST "${EXPERIMENTAL_BFS_TEST_SRCS}")
 
+###################################################################################################
+# - Experimental BFS tests ------------------------------------------------------------------------
+
+set(EXPERIMENTAL_MSBFS_TEST_SRCS
+    "${CMAKE_CURRENT_SOURCE_DIR}/experimental/ms_bfs_test.cpp")
+
+ConfigureTest(EXPERIMENTAL_MSBFS_TEST "${EXPERIMENTAL_MSBFS_TEST_SRCS}")
+
+
 ###################################################################################################
 # - Experimental SSSP tests -----------------------------------------------------------------------
 

cpp/tests/experimental/streams.cu

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2021, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governin_from_mtxg permissions and
+ * limitations under the License.
+ */
+
+#include <raft/cudart_utils.h>
+#include <thrust/transform.h>
+#include <raft/handle.hpp>
+#include <rmm/device_uvector.hpp>
+#include <rmm/exec_policy.hpp>
+#include <rmm/mr/device/cuda_memory_resource.hpp>
+#include "gtest/gtest.h"
+struct StreamTest : public ::testing::Test {
+};
+TEST_F(StreamTest, basic_test)
+{
+  int n_streams = 4;
+  raft::handle_t handle(n_streams);
+
+  const size_t intput_size = 4096;
+
+#pragma omp parallel for
+  for (int i = 0; i < n_streams; i++) {
+    rmm::device_uvector<int> u(intput_size, handle.get_internal_stream_view(i)),
+      v(intput_size, handle.get_internal_stream_view(i));
+    thrust::transform(rmm::exec_policy(handle.get_internal_stream_view(i)),
+                      u.begin(),
+                      u.end(),
+                      v.begin(),
+                      v.begin(),
+                      2 * thrust::placeholders::_1 + thrust::placeholders::_2);
+  }
+}

python/cugraph/__init__.py

@@ -82,7 +82,9 @@
     shortest_path,
     filter_unreachable,
     shortest_path_length,
-    traveling_salesperson
+    traveling_salesperson,
+    concurrent_bfs,
+    multi_source_bfs,
 )
 
 from cugraph.tree import minimum_spanning_tree, maximum_spanning_tree

python/cugraph/tests/test_egonet.py

@@ -58,29 +58,6 @@ def test_ego_graph_nx(graph_file, seed, radius):
 @pytest.mark.parametrize("seeds", [[0, 5, 13]])
 @pytest.mark.parametrize("radius", [1, 2, 3])
 def test_batched_ego_graphs(graph_file, seeds, radius):
-    """
-    Compute the  induced subgraph of neighbors for each node in seeds
-    within a given radius.
-    Parameters
-    ----------
-    G : cugraph.Graph, networkx.Graph, CuPy or SciPy sparse matrix
-        Graph or matrix object, which should contain the connectivity
-        information. Edge weights, if present, should be single or double
-        precision floating point values.
-    seeds : cudf.Series
-        Specifies the seeds of the induced egonet subgraphs
-    radius: integer, optional
-        Include all neighbors of distance<=radius from n.
-
-    Returns
-    -------
-    ego_edge_lists : cudf.DataFrame
-        GPU data frame containing all induced sources identifiers,
-        destination identifiers, edge weights
-    seeds_offsets: cudf.Series
-        Series containing the starting offset in the returned edge list
-        for each seed.
-    """
     gc.collect()
 
     # Nx
@@ -93,9 +70,8 @@ def test_batched_ego_graphs(graph_file, seeds, radius):
     df, offsets = cugraph.batched_ego_graphs(Gnx, seeds, radius=radius)
     for i in range(len(seeds)):
         ego_nx = nx.ego_graph(Gnx, seeds[i], radius=radius)
-        ego_df = df[offsets[i]:offsets[i+1]]
-        ego_cugraph = nx.from_pandas_edgelist(ego_df,
-                                              source="src",
-                                              target="dst",
-                                              edge_attr="weight")
+        ego_df = df[offsets[i]:offsets[i + 1]]
+        ego_cugraph = nx.from_pandas_edgelist(
+            ego_df, source="src", target="dst", edge_attr="weight"
+        )
     assert nx.is_isomorphic(ego_nx, ego_cugraph)

python/cugraph/traversal/__init__.py

@@ -17,6 +17,8 @@
     sssp,
     shortest_path,
     filter_unreachable,
-    shortest_path_length
+    shortest_path_length,
 )
 from cugraph.traversal.traveling_salesperson import traveling_salesperson
+
+from cugraph.traversal.ms_bfs import concurrent_bfs, multi_source_bfs