diff --git a/internal/ceres/parallel_invoke.cc b/internal/ceres/parallel_invoke.cc
new file mode 100644
index 0000000..0e387c5
--- /dev/null
+++ b/internal/ceres/parallel_invoke.cc
@@ -0,0 +1,77 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2023 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   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.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// 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 "ceres/parallel_vector_ops.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, [this]() { return num_total_jobs_finished_ == num_total_jobs_; });
+}
+
+ParallelInvokeState::ParallelInvokeState(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) {}
+
+}  // namespace ceres::internal