MySQL  8.0.26
Source Code Documentation
my_atomic.h
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1 #ifndef MY_ATOMIC_INCLUDED
2 #define MY_ATOMIC_INCLUDED
3 
4 /* Copyright (c) 2006, 2021, Oracle and/or its affiliates.
5 
6  This program is free software; you can redistribute it and/or modify
7  it under the terms of the GNU General Public License, version 2.0,
8  as published by the Free Software Foundation.
9 
10  This program is also distributed with certain software (including
11  but not limited to OpenSSL) that is licensed under separate terms,
12  as designated in a particular file or component or in included license
13  documentation. The authors of MySQL hereby grant you an additional
14  permission to link the program and your derivative works with the
15  separately licensed software that they have included with MySQL.
16 
17  This program is distributed in the hope that it will be useful,
18  but WITHOUT ANY WARRANTY; without even the implied warranty of
19  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20  GNU General Public License, version 2.0, for more details.
21 
22  You should have received a copy of the GNU General Public License
23  along with this program; if not, write to the Free Software
24  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
25 
26 /**
27  @file include/my_atomic.h
28 */
29 
30 #if defined(_MSC_VER)
31 
32 #include <windows.h>
33 
34 /*
35  my_yield_processor (equivalent of x86 PAUSE instruction) should be used
36  to improve performance on hyperthreaded CPUs. Intel recommends to use it in
37  spin loops also on non-HT machines to reduce power consumption (see e.g
38  http://softwarecommunity.intel.com/articles/eng/2004.htm)
39 
40  Running benchmarks for spinlocks implemented with InterlockedCompareExchange
41  and YieldProcessor shows that much better performance is achieved by calling
42  YieldProcessor in a loop - that is, yielding longer. On Intel boxes setting
43  loop count in the range 200-300 brought best results.
44  */
45 #define YIELD_LOOPS 200
46 
47 static inline int my_yield_processor() {
48  int i;
49  for (i = 0; i < YIELD_LOOPS; i++) {
50  YieldProcessor();
51  }
52  return 1;
53 }
54 
55 #define LF_BACKOFF my_yield_processor()
56 
57 #else // !defined(_MSC_VER)
58 
59 #define LF_BACKOFF (1)
60 
61 #endif
62 
63 #endif /* MY_ATOMIC_INCLUDED */