internal/ceres/parallel_for_cxx.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.
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//   and/or other materials provided with the distribution.
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// Author: vitus@google.com (Michael Vitus)

#include <algorithm>
#include <atomic>
#include <cmath>
#include <condition_variable>
#include <memory>
#include <mutex>
#include <tuple>

#include "ceres/internal/config.h"
#include "ceres/parallel_for.h"
#include "glog/logging.h"

namespace ceres::internal {

BlockUntilFinished::BlockUntilFinished(int num_total_jobs)
    : num_total_jobs_finished_(0), num_total_jobs_(num_total_jobs) {}

void BlockUntilFinished::Finished(int num_jobs_finished) {
  if (num_jobs_finished == 0) return;
  std::lock_guard<std::mutex> lock(mutex_);
  num_total_jobs_finished_ += num_jobs_finished;
  CHECK_LE(num_total_jobs_finished_, num_total_jobs_);
  if (num_total_jobs_finished_ == num_total_jobs_) {
    condition_.notify_one();
  }
}

void BlockUntilFinished::Block() {
  std::unique_lock<std::mutex> lock(mutex_);
  condition_.wait(
      lock, [&]() { return num_total_jobs_finished_ == num_total_jobs_; });
}

ThreadPoolState::ThreadPoolState(int start,
                                 int end,
                                 int num_work_blocks)
    : start(start),
      end(end),
      num_work_blocks(num_work_blocks),
      base_block_size((end - start) / num_work_blocks),
      num_base_p1_sized_blocks((end - start) % num_work_blocks),
      block_id(0),
      thread_id(0),
      block_until_finished(num_work_blocks) {}

int MaxNumThreadsAvailable() { return ThreadPool::MaxNumThreadsAvailable(); }

void ParallelSetZero(ContextImpl* context,
                     int num_threads,
                     double* values,
                     int num_values) {
  ParallelFor(context,
              0,
              num_values,
              num_threads,
              [values](std::tuple<int, int> range) {
                auto [start, end] = range;
                std::fill(values + start, values + end, 0.);
              });
}

}  // namespace ceres::internal