internal/ceres/parallel_for_openmp.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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// Author: vitus@google.com (Michael Vitus)

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

#if defined(CERES_USE_OPENMP)

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

namespace ceres {
namespace internal {

int MaxNumThreadsAvailable() { return omp_get_max_threads(); }

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

#ifdef CERES_USE_OPENMP
#pragma omp parallel for num_threads(num_threads) \
    schedule(dynamic) if (num_threads > 1)
#endif  // CERES_USE_OPENMP
  for (int i = start; i < end; ++i) {
    function(i);
  }
}

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

  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  // defined(CERES_USE_OPENMP)