1/* elide.h: Generic lock elision support.
2 Copyright (C) 2014-2016 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18#ifndef ELIDE_H
19#define ELIDE_H 1
20
21#include <hle.h>
22#include <elision-conf.h>
23
24#define ACCESS_ONCE(x) (* (volatile typeof(x) *) &(x))
25
26/* Adapt elision with ADAPT_COUNT and STATUS and decide retries. */
27
28static inline bool
29elision_adapt(signed char *adapt_count, unsigned int status)
30{
31 if (status & _XABORT_RETRY)
32 return false;
33 if ((status & _XABORT_EXPLICIT)
34 && _XABORT_CODE (status) == _ABORT_LOCK_BUSY)
35 {
36 /* Right now we skip here. Better would be to wait a bit
37 and retry. This likely needs some spinning. Be careful
38 to avoid writing the lock. */
39 if (*adapt_count != __elision_aconf.skip_lock_busy)
40 ACCESS_ONCE (*adapt_count) = __elision_aconf.skip_lock_busy;
41 }
42 /* Internal abort. There is no chance for retry.
43 Use the normal locking and next time use lock.
44 Be careful to avoid writing to the lock. */
45 else if (*adapt_count != __elision_aconf.skip_lock_internal_abort)
46 ACCESS_ONCE (*adapt_count) = __elision_aconf.skip_lock_internal_abort;
47 return true;
48}
49
50/* is_lock_free must be executed inside the transaction */
51
52/* Returns true if lock defined by IS_LOCK_FREE was elided.
53 ADAPT_COUNT is a pointer to per-lock state variable. */
54
55#define ELIDE_LOCK(adapt_count, is_lock_free) \
56 ({ \
57 int ret = 0; \
58 \
59 if ((adapt_count) <= 0) \
60 { \
61 for (int i = __elision_aconf.retry_try_xbegin; i > 0; i--) \
62 { \
63 unsigned int status; \
64 if ((status = _xbegin ()) == _XBEGIN_STARTED) \
65 { \
66 if (is_lock_free) \
67 { \
68 ret = 1; \
69 break; \
70 } \
71 _xabort (_ABORT_LOCK_BUSY); \
72 } \
73 if (!elision_adapt (&(adapt_count), status)) \
74 break; \
75 } \
76 } \
77 else \
78 (adapt_count)--; /* missing updates ok */ \
79 ret; \
80 })
81
82/* Returns true if lock defined by IS_LOCK_FREE was try-elided.
83 ADAPT_COUNT is a pointer to per-lock state variable. */
84
85#define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) ({ \
86 int ret = 0; \
87 if (__elision_aconf.retry_try_xbegin > 0) \
88 { \
89 if (write) \
90 _xabort (_ABORT_NESTED_TRYLOCK); \
91 ret = ELIDE_LOCK (adapt_count, is_lock_free); \
92 } \
93 ret; \
94 })
95
96/* Returns true if lock defined by IS_LOCK_FREE was elided. The call
97 to _xend crashes if the application incorrectly tries to unlock a
98 lock which has not been locked. */
99
100#define ELIDE_UNLOCK(is_lock_free) \
101 ({ \
102 int ret = 0; \
103 if (is_lock_free) \
104 { \
105 _xend (); \
106 ret = 1; \
107 } \
108 ret; \
109 })
110
111#endif
112