| 1 | /* elision-lock.c: Elided pthread mutex lock. |
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| 2 | Copyright (C) 2015-2024 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | The GNU C Library is distributed in the hope that it will be useful, |
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 13 | Lesser General Public License for more details. |
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| 14 | |
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| 15 | You should have received a copy of the GNU Lesser General Public |
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| 16 | License along with the GNU C Library; if not, see |
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| 17 | <https://www.gnu.org/licenses/>. */ |
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| 18 | |
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| 19 | #include <stdio.h> |
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| 20 | #include <pthread.h> |
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| 21 | #include <pthreadP.h> |
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| 22 | #include <lowlevellock.h> |
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| 23 | #include <elision-conf.h> |
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| 24 | #include "htm.h" |
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| 25 | |
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| 26 | #ifndef EXTRAARG |
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| 27 | # define |
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| 28 | #endif |
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| 29 | #ifndef LLL_LOCK |
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| 30 | # define LLL_LOCK(a,b) lll_lock(a,b), 0 |
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| 31 | #endif |
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| 32 | |
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| 33 | #define aconf __elision_aconf |
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| 34 | |
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| 35 | /* Adaptive lock using transactions. |
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| 36 | By default the lock region is run as a transaction, and when it |
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| 37 | aborts or the lock is busy the lock adapts itself. */ |
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| 38 | |
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| 39 | int |
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| 40 | __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared) |
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| 41 | { |
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| 42 | /* adapt_count is accessed concurrently but is just a hint. Thus, |
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| 43 | use atomic accesses but relaxed MO is sufficient. */ |
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| 44 | if (atomic_load_relaxed (adapt_count) > 0) |
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| 45 | { |
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| 46 | goto use_lock; |
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| 47 | } |
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| 48 | |
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| 49 | for (int i = aconf.try_tbegin; i > 0; i--) |
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| 50 | { |
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| 51 | if (__libc_tbegin (0)) |
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| 52 | { |
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| 53 | if (*lock == 0) |
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| 54 | return 0; |
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| 55 | /* Lock was busy. Fall back to normal locking. */ |
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| 56 | __libc_tabort (_ABORT_LOCK_BUSY); |
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| 57 | } |
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| 58 | else |
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| 59 | { |
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| 60 | /* A persistent failure indicates that a retry will probably |
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| 61 | result in another failure. Use normal locking now and |
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| 62 | for the next couple of calls. */ |
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| 63 | if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ())) |
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| 64 | { |
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| 65 | if (aconf.skip_lock_internal_abort > 0) |
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| 66 | atomic_store_relaxed (adapt_count, |
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| 67 | aconf.skip_lock_internal_abort); |
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| 68 | goto use_lock; |
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| 69 | } |
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| 70 | } |
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| 71 | } |
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| 72 | |
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| 73 | /* Fall back to locks for a bit if retries have been exhausted */ |
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| 74 | if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0) |
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| 75 | atomic_store_relaxed (adapt_count, |
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| 76 | aconf.skip_lock_out_of_tbegin_retries); |
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| 77 | |
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| 78 | use_lock: |
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| 79 | return LLL_LOCK ((*lock), pshared); |
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| 80 | } |
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| 81 | libc_hidden_def (__lll_lock_elision) |
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| 82 | |
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