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diff --git a/tools/thread_pool_internal.h b/tools/thread_pool_internal.h
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+// Copyright (c) the JPEG XL Project Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#ifndef TOOLS_THREAD_POOL_INTERNAL_H_
+#define TOOLS_THREAD_POOL_INTERNAL_H_
+
+#include <jxl/thread_parallel_runner_cxx.h>
+#include <stddef.h>
+
+#include <cmath>
+#include <thread>  // NOLINT
+
+#include "lib/jxl/base/data_parallel.h"
+
+namespace jpegxl {
+namespace tools {
+
+using ::jxl::ThreadPool;
+
+// Helper class to pass an internal ThreadPool-like object using threads.
+class ThreadPoolInternal {
+ public:
+  // Starts the given number of worker threads and blocks until they are ready.
+  // "num_worker_threads" defaults to one per hyperthread. If zero, all tasks
+  // run on the main thread.
+  explicit ThreadPoolInternal(
+      size_t num_threads = std::thread::hardware_concurrency()) {
+    runner_ =
+        JxlThreadParallelRunnerMake(/* memory_manager */ nullptr, num_threads);
+    pool_.reset(new ThreadPool(JxlThreadParallelRunner, runner_.get()));
+  }
+
+  ThreadPoolInternal(const ThreadPoolInternal&) = delete;
+  ThreadPoolInternal& operator&(const ThreadPoolInternal&) = delete;
+  ThreadPool* operator&() { return pool_.get(); }
+
+ private:
+  JxlThreadParallelRunnerPtr runner_;
+  std::unique_ptr<ThreadPool> pool_;
+};
+
+}  // namespace tools
+}  // namespace jpegxl
+
+#endif  // TOOLS_THREAD_POOL_INTERNAL_H_