text: //
  // Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2019
  //
  // Distributed under the Boost Software License, Version 1.0. (See accompanying
  // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  //
  #pragma once
  
  #include "td/utils/port/thread.h"
  
  #include <atomic>
  #include <memory>
  
  namespace td {
  
  class SpinLock {
    struct Unlock {
      void operator()(SpinLock *ptr) {
        ptr->unlock();
      }
    };
  
    class InfBackoff {
      int cnt = 0;
  
     public:
      bool next() {
        cnt++;
        if (cnt < 50) {
          return true;
        } else {
          td::this_thread::yield();
          return true;
        }
      }
    };
  
   public:
    using Lock = std::unique_ptr<SpinLock, Unlock>;
  
    Lock lock() {
      InfBackoff backoff;
      while (!try_lock()) {
        backoff.next();
      }
      return Lock(this);
    }
    bool try_lock() {
      return !flag_.test_and_set(std::memory_order_acquire);
    }
  
   private:
    std::atomic_flag flag_ = ATOMIC_FLAG_INIT;
    void unlock() {
      flag_.clear(std::memory_order_release);
    }
  };
  
  }  // namespace td
  