libcxx/include/__thread/timed_backoff_policy.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___THREAD_TIMED_BACKOFF_POLICY_H
  11 #define _LIBCPP___THREAD_TIMED_BACKOFF_POLICY_H
  12
  13 #include <__config>
  14
  15 #ifndef _LIBCPP_HAS_NO_THREADS
  16
  17 #  include <__chrono/duration.h>
  18 #  include <__threading_support>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_BEGIN_NAMESPACE_STD
  25
  26 struct __libcpp_timed_backoff_policy {
  27   _LIBCPP_INLINE_VISIBILITY
  28   bool operator()(chrono::nanoseconds __elapsed) const
  29   {
  30       if(__elapsed > chrono::milliseconds(128))
  31           __libcpp_thread_sleep_for(chrono::milliseconds(8));
  32       else if(__elapsed > chrono::microseconds(64))
  33           __libcpp_thread_sleep_for(__elapsed / 2);
  34       else if(__elapsed > chrono::microseconds(4))
  35         __libcpp_thread_yield();
  36       else
  37         {} // poll
  38       return false;
  39   }
  40 };
  41
  42 _LIBCPP_END_NAMESPACE_STD
  43
  44 #endif // _LIBCPP_HAS_NO_THREADS
  45
  46 #endif // _LIBCPP___THREAD_TIMED_BACKOFF_POLICY_H