[rabit] Drop support for MPI backend. (#9525)

- Add checks in cmake.
- Remove mpi related code.

CMakeLists.txt

@@ -47,7 +47,6 @@ option(USE_OPENMP "Build with OpenMP support." ON)
 option(BUILD_STATIC_LIB "Build static library" OFF)
 option(BUILD_DEPRECATED_CLI "Build the deprecated command line interface" OFF)
 option(FORCE_SHARED_CRT "Build with dynamic CRT on Windows (/MD)" OFF)
-option(RABIT_BUILD_MPI "Build MPI" OFF)
 ## Bindings
 option(JVM_BINDINGS "Build JVM bindings" OFF)
 option(R_LIB "Build shared library for R package" OFF)
@@ -106,12 +105,6 @@ if (R_LIB AND GOOGLE_TEST)
   message(WARNING "Some C++ unittests will fail with `R_LIB` enabled,
  as R package redirects some functions to R runtime implementation.")
 endif (R_LIB AND GOOGLE_TEST)
-if (USE_AVX)
-  message(SEND_ERROR  "The option 'USE_AVX' is deprecated as experimental AVX features have been removed from XGBoost.")
-endif (USE_AVX)
-if (PLUGIN_LZ4)
-  message(SEND_ERROR  "The option 'PLUGIN_LZ4' is removed from XGBoost.")
-endif (PLUGIN_LZ4)
 if (PLUGIN_RMM AND NOT (USE_CUDA))
   message(SEND_ERROR "`PLUGIN_RMM` must be enabled with `USE_CUDA` flag.")
 endif (PLUGIN_RMM AND NOT (USE_CUDA))
@@ -144,6 +137,26 @@ if (PLUGIN_FEDERATED)
   endif ()
 endif ()
 
+#-- Removed options
+if (USE_AVX)
+  message(SEND_ERROR  "The option `USE_AVX` is deprecated as experimental AVX features have been removed from XGBoost.")
+endif (USE_AVX)
+if (PLUGIN_LZ4)
+  message(SEND_ERROR  "The option `PLUGIN_LZ4` is removed from XGBoost.")
+endif (PLUGIN_LZ4)
+if (RABIT_BUILD_MPI)
+  message(SEND_ERROR "The option `RABIT_BUILD_MPI` has been removed from XGBoost.")
+endif (RABIT_BUILD_MPI)
+if (USE_S3)
+  message(SEND_ERROR "The option `USE_S3` has been removed from XGBoost")
+endif (USE_S3)
+if (USE_AZURE)
+  message(SEND_ERROR "The option `USE_AZURE` has been removed from XGBoost")
+endif (USE_AZURE)
+if (USE_HDFS)
+  message(SEND_ERROR "The option `USE_HDFS` has been removed from XGBoost")
+endif (USE_HDFS)
+
 #-- Sanitizer
 if (USE_SANITIZER)
   include(cmake/Sanitizer.cmake)
@@ -222,9 +235,6 @@ endif (MSVC)
 
 # rabit
 add_subdirectory(rabit)
-if (RABIT_BUILD_MPI)
-  find_package(MPI REQUIRED)
-endif (RABIT_BUILD_MPI)
 
 # core xgboost
 add_subdirectory(${xgboost_SOURCE_DIR}/src)

cmake/Utils.cmake

@@ -295,10 +295,6 @@ macro(xgboost_target_link_libraries target)
     target_link_libraries(${target} PRIVATE CUDA::nvToolsExt)
   endif (USE_NVTX)
 
-  if (RABIT_BUILD_MPI)
-    target_link_libraries(${target} PRIVATE MPI::MPI_CXX)
-  endif (RABIT_BUILD_MPI)
-
   if (MINGW)
     target_link_libraries(${target} PRIVATE wsock32 ws2_32)
   endif (MINGW)

rabit/CMakeLists.txt

@@ -6,9 +6,7 @@ set(RABIT_SOURCES
   ${CMAKE_CURRENT_LIST_DIR}/src/allreduce_base.cc
   ${CMAKE_CURRENT_LIST_DIR}/src/rabit_c_api.cc)
 
-if (RABIT_BUILD_MPI)
+if (RABIT_MOCK)
-  list(APPEND RABIT_SOURCES ${CMAKE_CURRENT_LIST_DIR}/src/engine_mpi.cc)
-elseif (RABIT_MOCK)
   list(APPEND RABIT_SOURCES ${CMAKE_CURRENT_LIST_DIR}/src/engine_mock.cc)
 else ()
   list(APPEND RABIT_SOURCES ${CMAKE_CURRENT_LIST_DIR}/src/engine.cc)

rabit/src/engine_mpi.cc

@@ -1,162 +0,0 @@
-/*!
- *  Copyright (c) 2014 by Contributors
- * \file engine_mpi.cc
- * \brief this file gives an implementation of engine interface using MPI,
- *   this will allow rabit program to run with MPI, but do not comes with fault tolerant
- *
- * \author Tianqi Chen
- */
-#define NOMINMAX
-#include <mpi.h>
-#include <rabit/base.h>
-#include <cstdio>
-#include <string>
-#include "rabit/internal/engine.h"
-#include "rabit/internal/utils.h"
-
-namespace rabit {
-namespace engine {
-/*! \brief implementation of engine using MPI */
-class MPIEngine : public IEngine {
- public:
-  MPIEngine(void) {
-    version_number = 0;
-  }
-  void Allgather(void *sendrecvbuf_, size_t total_size, size_t slice_begin,
-                 size_t slice_end, size_t size_prev_slice) override {
-    utils::Error("MPIEngine:: Allgather is not supported");
-  }
-  void Allreduce(void *sendrecvbuf_, size_t type_nbytes, size_t count,
-                 ReduceFunction reducer, PreprocFunction prepare_fun,
-                 void *prepare_arg) override {
-    utils::Error("MPIEngine:: Allreduce is not supported,"\
-                 "use Allreduce_ instead");
-  }
-  int GetRingPrevRank(void) const override {
-    utils::Error("MPIEngine:: GetRingPrevRank is not supported");
-    return -1;
-  }
-  void Broadcast(void *sendrecvbuf_, size_t size, int root) override {
-    MPI::COMM_WORLD.Bcast(sendrecvbuf_, size, MPI::CHAR, root);
-  }
-  virtual void InitAfterException(void) {
-    utils::Error("MPI is not fault tolerant");
-  }
-  virtual int LoadCheckPoint(Serializable *global_model,
-                             Serializable *local_model = NULL) {
-    return 0;
-  }
-  virtual void CheckPoint(const Serializable *global_model,
-                          const Serializable *local_model = NULL) {
-    version_number += 1;
-  }
-  virtual void LazyCheckPoint(const Serializable *global_model) {
-    version_number += 1;
-  }
-  virtual int VersionNumber(void) const {
-    return version_number;
-  }
-  /*! \brief get rank of current node */
-  virtual int GetRank(void) const {
-    return MPI::COMM_WORLD.Get_rank();
-  }
-  /*! \brief get total number of */
-  virtual int GetWorldSize(void) const {
-    return MPI::COMM_WORLD.Get_size();
-  }
-  /*! \brief whether it is distributed */
-  virtual bool IsDistributed(void) const {
-    return true;
-  }
-  /*! \brief get the host name of current node */
-  virtual std::string GetHost(void) const {
-    int len;
-    char name[MPI_MAX_PROCESSOR_NAME];
-    MPI::Get_processor_name(name, len);
-    name[len] = '\0';
-    return std::string(name);
-  }
-  virtual void TrackerPrint(const std::string &msg) {
-    // simply print information into the tracker
-    if (GetRank() == 0) {
-      utils::Printf("%s", msg.c_str());
-    }
-  }
-
- private:
-  int version_number;
-};
-
-// singleton sync manager
-MPIEngine manager;
-
-/*! \brief initialize the synchronization module */
-bool Init(int argc, char *argv[]) {
-  try {
-    MPI::Init(argc, argv);
-    return true;
-  } catch (const std::exception& e) {
-    fprintf(stderr, " failed in MPI Init %s\n", e.what());
-    return false;
-  }
-}
-/*! \brief finalize syncrhonization module */
-bool Finalize(void) {
-  try {
-    MPI::Finalize();
-    return true;
-  } catch (const std::exception& e) {
-    fprintf(stderr, "failed in MPI shutdown %s\n", e.what());
-    return false;
-  }
-}
-
-/*! \brief singleton method to get engine */
-IEngine *GetEngine(void) {
-  return &manager;
-}
-// transform enum to MPI data type
-inline MPI::Datatype GetType(mpi::DataType dtype) {
-  using namespace mpi;
-  switch (dtype) {
-    case kChar: return MPI::CHAR;
-    case kUChar: return MPI::BYTE;
-    case kInt: return MPI::INT;
-    case kUInt: return MPI::UNSIGNED;
-    case kLong: return MPI::LONG;
-    case kULong: return MPI::UNSIGNED_LONG;
-    case kFloat: return MPI::FLOAT;
-    case kDouble: return MPI::DOUBLE;
-    case kLongLong: return MPI::LONG_LONG;
-    case kULongLong: return MPI::UNSIGNED_LONG_LONG;
-  }
-  utils::Error("unknown mpi::DataType");
-  return MPI::CHAR;
-}
-// transform enum to MPI OP
-inline MPI::Op GetOp(mpi::OpType otype) {
-  using namespace mpi;
-  switch (otype) {
-    case kMax: return MPI::MAX;
-    case kMin: return MPI::MIN;
-    case kSum: return MPI::SUM;
-    case kBitwiseOR: return MPI::BOR;
-  }
-  utils::Error("unknown mpi::OpType");
-  return MPI::MAX;
-}
-// perform in-place allreduce, on sendrecvbuf
-void Allreduce_(void *sendrecvbuf,
-                size_t type_nbytes,
-                size_t count,
-                IEngine::ReduceFunction red,
-                mpi::DataType dtype,
-                mpi::OpType op,
-                IEngine::PreprocFunction prepare_fun,
-                void *prepare_arg) {
-  if (prepare_fun != NULL) prepare_fun(prepare_arg);
-  MPI::COMM_WORLD.Allreduce(MPI_IN_PLACE, sendrecvbuf,
-                            count, GetType(dtype), GetOp(op));
-}
-}  // namespace engine
-}  // namespace rabit