Common interface for collective communication (#8057)

* implement broadcast for federated communicator

* implement allreduce

* add communicator factory

* add device adapter

* add device communicator to factory

* add rabit communicator

* add rabit communicator to the factory

* add nccl device communicator

* add synchronize to device communicator

* add back print and getprocessorname

* add python wrapper and c api

* clean up types

* fix non-gpu build

* try to fix ci

* fix std::size_t

* portable string compare ignore case

* c style size_t

* fix lint errors

* cross platform setenv

* fix memory leak

* fix lint errors

* address review feedback

* add python test for rabit communicator

* fix failing gtest

* use json to configure communicators

* fix lint error

* get rid of factories

* fix cpu build

* fix include

* fix python import

* don't export collective.py yet

* skip collective communicator pytest on windows

* add review feedback

* update documentation

* remove mpi communicator type

* fix tests

* shutdown the communicator separately

Co-authored-by: Hyunsu Cho <chohyu01@cs.washington.edu>

tests/cpp/plugin/test_federated_communicator.cc

@@ -0,0 +1,119 @@
+/*!
+ * Copyright 2022 XGBoost contributors
+ */
+#include <dmlc/parameter.h>
+#include <grpcpp/server_builder.h>
+#include <gtest/gtest.h>
+
+#include <thread>
+
+#include "../../../plugin/federated/federated_communicator.h"
+#include "../../../plugin/federated/federated_server.h"
+
+namespace xgboost {
+namespace collective {
+
+std::string const kServerAddress{"localhost:56789"};  // NOLINT(cert-err58-cpp)
+
+class FederatedCommunicatorTest : public ::testing::Test {
+ public:
+  static void VerifyAllreduce(int rank) {
+    FederatedCommunicator comm{kWorldSize, rank, kServerAddress};
+    CheckAllreduce(comm);
+  }
+
+  static void VerifyBroadcast(int rank) {
+    FederatedCommunicator comm{kWorldSize, rank, kServerAddress};
+    CheckBroadcast(comm, rank);
+  }
+
+ protected:
+  void SetUp() override {
+    server_thread_.reset(new std::thread([this] {
+      grpc::ServerBuilder builder;
+      federated::FederatedService service{kWorldSize};
+      builder.AddListeningPort(kServerAddress, grpc::InsecureServerCredentials());
+      builder.RegisterService(&service);
+      server_ = builder.BuildAndStart();
+      server_->Wait();
+    }));
+  }
+
+  void TearDown() override {
+    server_->Shutdown();
+    server_thread_->join();
+  }
+
+  static void CheckAllreduce(FederatedCommunicator &comm) {
+    int buffer[] = {1, 2, 3, 4, 5};
+    comm.AllReduce(buffer, sizeof(buffer) / sizeof(buffer[0]), DataType::kInt32, Operation::kSum);
+    int expected[] = {3, 6, 9, 12, 15};
+    for (auto i = 0; i < 5; i++) {
+      EXPECT_EQ(buffer[i], expected[i]);
+    }
+  }
+
+  static void CheckBroadcast(FederatedCommunicator &comm, int rank) {
+    if (rank == 0) {
+      std::string buffer{"hello"};
+      comm.Broadcast(&buffer[0], buffer.size(), 0);
+      EXPECT_EQ(buffer, "hello");
+    } else {
+      std::string buffer{"     "};
+      comm.Broadcast(&buffer[0], buffer.size(), 0);
+      EXPECT_EQ(buffer, "hello");
+    }
+  }
+
+  static int const kWorldSize{3};
+  std::unique_ptr<std::thread> server_thread_;
+  std::unique_ptr<grpc::Server> server_;
+};
+
+TEST(FederatedCommunicatorSimpleTest, ThrowOnWorldSizeTooSmall) {
+  auto construct = []() { FederatedCommunicator comm{0, 0, kServerAddress, "", "", ""}; };
+  EXPECT_THROW(construct(), dmlc::Error);
+}
+
+TEST(FederatedCommunicatorSimpleTest, ThrowOnRankTooSmall) {
+  auto construct = []() { FederatedCommunicator comm{1, -1, kServerAddress, "", "", ""}; };
+  EXPECT_THROW(construct(), dmlc::Error);
+}
+
+TEST(FederatedCommunicatorSimpleTest, ThrowOnRankTooBig) {
+  auto construct = []() { FederatedCommunicator comm{1, 1, kServerAddress, "", "", ""}; };
+  EXPECT_THROW(construct(), dmlc::Error);
+}
+
+TEST(FederatedCommunicatorSimpleTest, GetWorldSizeAndRank) {
+  FederatedCommunicator comm{6, 3, kServerAddress};
+  EXPECT_EQ(comm.GetWorldSize(), 6);
+  EXPECT_EQ(comm.GetRank(), 3);
+}
+
+TEST(FederatedCommunicatorSimpleTest, IsDistributed) {
+  FederatedCommunicator comm{2, 1, kServerAddress};
+  EXPECT_TRUE(comm.IsDistributed());
+}
+
+TEST_F(FederatedCommunicatorTest, Allreduce) {
+  std::vector<std::thread> threads;
+  for (auto rank = 0; rank < kWorldSize; rank++) {
+    threads.emplace_back(std::thread(&FederatedCommunicatorTest::VerifyAllreduce, rank));
+  }
+  for (auto &thread : threads) {
+    thread.join();
+  }
+}
+
+TEST_F(FederatedCommunicatorTest, Broadcast) {
+  std::vector<std::thread> threads;
+  for (auto rank = 0; rank < kWorldSize; rank++) {
+    threads.emplace_back(std::thread(&FederatedCommunicatorTest::VerifyBroadcast, rank));
+  }
+  for (auto &thread : threads) {
+    thread.join();
+  }
+}
+}  // namespace collective
+}  // namespace xgboost