my_atomic.h

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#ifndef MY_ATOMIC_INCLUDED
#define MY_ATOMIC_INCLUDED
 
/* Copyright (c) 2006, 2024, Oracle and/or its affiliates.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
   This program is designed to work with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have either included with
   the program or referenced in the documentation.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
/**
  @file include/my_atomic.h
*/
 
#if defined(_MSC_VER)
 
#include <windows.h>
 
/*
  my_yield_processor (equivalent of x86 PAUSE instruction) should be used
  to improve performance on hyperthreaded CPUs. Intel recommends to use it in
  spin loops also on non-HT machines to reduce power consumption (see e.g
  http://softwarecommunity.intel.com/articles/eng/2004.htm)
 
  Running benchmarks for spinlocks implemented with InterlockedCompareExchange
  and YieldProcessor shows that much better performance is achieved by calling
  YieldProcessor in a loop - that is, yielding longer. On Intel boxes setting
  loop count in the range 200-300 brought best results.
 */
#define YIELD_LOOPS 200
 
static inline int my_yield_processor() {
  int i;
  for (i = 0; i < YIELD_LOOPS; i++) {
    YieldProcessor();
  }
  return 1;
}
 
#define LF_BACKOFF my_yield_processor()
 
#else  // !defined(_MSC_VER)
 
#define LF_BACKOFF (1)
 
#endif
 
#endif /* MY_ATOMIC_INCLUDED */