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1cdbe579 | 1 | /* elision-lock.c: Elided pthread mutex lock. |
b168057a | 2 | Copyright (C) 2011-2015 Free Software Foundation, Inc. |
1cdbe579 AK |
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 | |
075b9322 | 17 | <http://www.gnu.org/licenses/>. */ |
1cdbe579 AK |
18 | |
19 | #include <pthread.h> | |
20 | #include "pthreadP.h" | |
21 | #include "lowlevellock.h" | |
22 | #include "hle.h" | |
23 | #include <elision-conf.h> | |
24 | ||
25 | #if !defined(LLL_LOCK) && !defined(EXTRAARG) | |
26 | /* Make sure the configuration code is always linked in for static | |
27 | libraries. */ | |
28 | #include "elision-conf.c" | |
29 | #endif | |
30 | ||
31 | #ifndef EXTRAARG | |
32 | #define EXTRAARG | |
33 | #endif | |
34 | #ifndef LLL_LOCK | |
35 | #define LLL_LOCK(a,b) lll_lock(a,b), 0 | |
36 | #endif | |
37 | ||
38 | #define aconf __elision_aconf | |
39 | ||
40 | /* Adaptive lock using transactions. | |
41 | By default the lock region is run as a transaction, and when it | |
42 | aborts or the lock is busy the lock adapts itself. */ | |
43 | ||
44 | int | |
45 | __lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private) | |
46 | { | |
47 | if (*adapt_count <= 0) | |
48 | { | |
49 | unsigned status; | |
50 | int try_xbegin; | |
51 | ||
52 | for (try_xbegin = aconf.retry_try_xbegin; | |
53 | try_xbegin > 0; | |
54 | try_xbegin--) | |
55 | { | |
56 | if ((status = _xbegin()) == _XBEGIN_STARTED) | |
57 | { | |
58 | if (*futex == 0) | |
59 | return 0; | |
60 | ||
075b9322 | 61 | /* Lock was busy. Fall back to normal locking. |
1cdbe579 AK |
62 | Could also _xend here but xabort with 0xff code |
63 | is more visible in the profiler. */ | |
64 | _xabort (_ABORT_LOCK_BUSY); | |
65 | } | |
66 | ||
67 | if (!(status & _XABORT_RETRY)) | |
68 | { | |
69 | if ((status & _XABORT_EXPLICIT) | |
70 | && _XABORT_CODE (status) == _ABORT_LOCK_BUSY) | |
71 | { | |
075b9322 DV |
72 | /* Right now we skip here. Better would be to wait a bit |
73 | and retry. This likely needs some spinning. */ | |
1cdbe579 AK |
74 | if (*adapt_count != aconf.skip_lock_busy) |
75 | *adapt_count = aconf.skip_lock_busy; | |
76 | } | |
075b9322 | 77 | /* Internal abort. There is no chance for retry. |
1cdbe579 AK |
78 | Use the normal locking and next time use lock. |
79 | Be careful to avoid writing to the lock. */ | |
80 | else if (*adapt_count != aconf.skip_lock_internal_abort) | |
81 | *adapt_count = aconf.skip_lock_internal_abort; | |
82 | break; | |
83 | } | |
84 | } | |
85 | } | |
86 | else | |
87 | { | |
88 | /* Use a normal lock until the threshold counter runs out. | |
89 | Lost updates possible. */ | |
90 | (*adapt_count)--; | |
91 | } | |
92 | ||
93 | /* Use a normal lock here. */ | |
94 | return LLL_LOCK ((*futex), private); | |
95 | } |