1 /* Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
2
3 This program is free software; you can redistribute it and/or modify
4 it under the terms of the GNU General Public License, version 2.0,
5 as published by the Free Software Foundation.
6
7 This program is also distributed with certain software (including
8 but not limited to OpenSSL) that is licensed under separate terms,
9 as designated in a particular file or component or in included license
10 documentation. The authors of MySQL hereby grant you an additional
11 permission to link the program and your derivative works with the
12 separately licensed software that they have included with MySQL.
13
14 This program is distributed in the hope that it will be useful,
15 but WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 GNU General Public License, version 2.0, for more details.
18
19 You should have received a copy of the GNU General Public License
20 along with this program; if not, write to the Free Software
21 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA */
22
23 #ifndef NDB_SEQLOCK_HPP
24 #define NDB_SEQLOCK_HPP
25
26 #include <ndb_types.h>
27 #include "mt-asm.h"
28
29 #if defined (NDB_HAVE_RMB) && defined(NDB_HAVE_WMB)
30 struct NdbSeqLock
31 {
NdbSeqLockNdbSeqLock32 NdbSeqLock() { m_seq = 0;}
33 volatile Uint32 m_seq;
34
35 void write_lock();
36 void write_unlock();
37
38 Uint32 read_lock();
39 bool read_unlock(Uint32 val) const;
40 };
41
42 inline
43 void
write_lock()44 NdbSeqLock::write_lock()
45 {
46 assert((m_seq & 1) == 0);
47 m_seq++;
48 wmb();
49 }
50
51 inline
52 void
write_unlock()53 NdbSeqLock::write_unlock()
54 {
55 assert((m_seq & 1) == 1);
56 wmb();
57 m_seq++;
58 }
59
60 inline
61 Uint32
read_lock()62 NdbSeqLock::read_lock()
63 {
64 loop:
65 Uint32 val = m_seq;
66 rmb();
67 if (unlikely(val & 1))
68 {
69 #ifdef NDB_HAVE_CPU_PAUSE
70 cpu_pause();
71 #endif
72 goto loop;
73 }
74 return val;
75 }
76
77 inline
78 bool
read_unlock(Uint32 val) const79 NdbSeqLock::read_unlock(Uint32 val) const
80 {
81 rmb();
82 return val == m_seq;
83 }
84 #else /** ! rmb() or wmb() */
85 /**
86 * Only for ndbd...
87 */
88
89 struct NdbSeqLock
90 {
NdbSeqLockNdbSeqLock91 NdbSeqLock() { }
92
write_lockNdbSeqLock93 void write_lock() {}
write_unlockNdbSeqLock94 void write_unlock() {}
95
read_lockNdbSeqLock96 Uint32 read_lock() { return 0; }
read_unlockNdbSeqLock97 bool read_unlock(Uint32 val) const { return true;}
98 };
99
100 #endif
101
102 #endif
103