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1 | /* elide.h: Generic lock elision support. |
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2 | Copyright (C) 2014-2022 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 | <https://www.gnu.org/licenses/>. */ |
18 | #ifndef ELIDE_H |
19 | #define ELIDE_H 1 |
20 | |
21 | #include <hle.h> |
22 | #include <elision-conf.h> |
23 | #include <atomic.h> |
24 | |
25 | |
26 | /* Adapt elision with ADAPT_COUNT and STATUS and decide retries. */ |
27 | |
28 | static inline bool |
29 | elision_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 | Using relaxed MO and separate atomic accesses is sufficient because |
40 | adapt_count is just a hint. */ |
41 | if (atomic_load_relaxed (adapt_count) != __elision_aconf.skip_lock_busy) |
42 | atomic_store_relaxed (adapt_count, __elision_aconf.skip_lock_busy); |
43 | } |
44 | /* Internal abort. There is no chance for retry. |
45 | Use the normal locking and next time use lock. |
46 | Be careful to avoid writing to the lock. See above for MO. */ |
47 | else if (atomic_load_relaxed (adapt_count) |
48 | != __elision_aconf.skip_lock_internal_abort) |
49 | atomic_store_relaxed (adapt_count, |
50 | __elision_aconf.skip_lock_internal_abort); |
51 | return true; |
52 | } |
53 | |
54 | /* is_lock_free must be executed inside the transaction */ |
55 | |
56 | /* Returns true if lock defined by IS_LOCK_FREE was elided. |
57 | ADAPT_COUNT is a per-lock state variable; it must be accessed atomically |
58 | to avoid data races but is just a hint, so using relaxed MO and separate |
59 | atomic loads and stores instead of atomic read-modify-write operations is |
60 | sufficient. */ |
61 | |
62 | #define ELIDE_LOCK(adapt_count, is_lock_free) \ |
63 | ({ \ |
64 | int ret = 0; \ |
65 | \ |
66 | if (atomic_load_relaxed (&(adapt_count)) <= 0) \ |
67 | { \ |
68 | for (int i = __elision_aconf.retry_try_xbegin; i > 0; i--) \ |
69 | { \ |
70 | unsigned int status; \ |
71 | if ((status = _xbegin ()) == _XBEGIN_STARTED) \ |
72 | { \ |
73 | if (is_lock_free) \ |
74 | { \ |
75 | ret = 1; \ |
76 | break; \ |
77 | } \ |
78 | _xabort (_ABORT_LOCK_BUSY); \ |
79 | } \ |
80 | if (!elision_adapt (&(adapt_count), status)) \ |
81 | break; \ |
82 | } \ |
83 | } \ |
84 | else \ |
85 | atomic_store_relaxed (&(adapt_count), \ |
86 | atomic_load_relaxed (&(adapt_count)) - 1); \ |
87 | ret; \ |
88 | }) |
89 | |
90 | /* Returns true if lock defined by IS_LOCK_FREE was try-elided. |
91 | ADAPT_COUNT is a per-lock state variable. */ |
92 | |
93 | #define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) ({ \ |
94 | int ret = 0; \ |
95 | if (__elision_aconf.retry_try_xbegin > 0) \ |
96 | { \ |
97 | if (write) \ |
98 | _xabort (_ABORT_NESTED_TRYLOCK); \ |
99 | ret = ELIDE_LOCK (adapt_count, is_lock_free); \ |
100 | } \ |
101 | ret; \ |
102 | }) |
103 | |
104 | /* Returns true if lock defined by IS_LOCK_FREE was elided. The call |
105 | to _xend crashes if the application incorrectly tries to unlock a |
106 | lock which has not been locked. */ |
107 | |
108 | #define ELIDE_UNLOCK(is_lock_free) \ |
109 | ({ \ |
110 | int ret = 0; \ |
111 | if (is_lock_free) \ |
112 | { \ |
113 | _xend (); \ |
114 | ret = 1; \ |
115 | } \ |
116 | ret; \ |
117 | }) |
118 | |
119 | #endif |
120 |
Warning: That file was not part of the compilation database. It may have many parsing errors.