internal/ceres/parallel_for_tbb.cc

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2018 Google Inc. All rights reserved.
// http://ceres-solver.org/
//
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// modification, are permitted provided that the following conditions are met:
//
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//   this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
//   and/or other materials provided with the distribution.
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// Author: vitus@google.com (Michael Vitus)

// This include must come before any #ifndef check on Ceres compile options.
#include "ceres/internal/port.h"

#ifdef CERES_USE_TBB

#include "ceres/parallel_for.h"

#include <tbb/parallel_for.h>
#include <tbb/task_arena.h>

#include "ceres/scoped_thread_token.h"
#include "ceres/thread_token_provider.h"
#include "glog/logging.h"

namespace ceres {
namespace internal {

void ParallelFor(ContextImpl* context,
                 int start,
                 int end,
                 int num_threads,
                 const std::function<void(int)>& function) {
  CHECK_GT(num_threads, 0);
  CHECK(context != NULL);
  if (end <= start) {
    return;
  }

  // Fast path for when it is single threaded.
  if (num_threads == 1) {
    for (int i = start; i < end; ++i) {
      function(i);
    }
    return;
  }

  tbb::task_arena task_arena(num_threads);
  task_arena.execute([&]{
      tbb::parallel_for(start, end, function);
    });
}

void ParallelFor(ContextImpl* context,
                 int start,
                 int end,
                 int num_threads,
                 const std::function<void(int thread_id, int i)>& function) {
  CHECK(context != NULL);

  ThreadTokenProvider thread_token_provider(num_threads);
  ParallelFor(context, start, end, num_threads, [&](int i) {
    const ScopedThreadToken scoped_thread_token(&thread_token_provider);
    const int thread_id = scoped_thread_token.token();
    function(thread_id, i);
  });
}


}  // namespace internal
}  // namespace ceres

#endif // CERES_USE_TBB