| 1 | /* elision-trylock.c: Lock eliding trylock for pthreads. |
|---|---|
| 2 | Copyright (C) 2015-2022 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 | |
| 19 | #include <pthread.h> |
| 20 | #include <pthreadP.h> |
| 21 | #include <lowlevellock.h> |
| 22 | #include <elision-conf.h> |
| 23 | #include "htm.h" |
| 24 | |
| 25 | #define aconf __elision_aconf |
| 26 | |
| 27 | /* Try to elide a futex trylock. FUTEX is the futex variable. ADAPT_COUNT is |
| 28 | the adaptation counter in the mutex. */ |
| 29 | |
| 30 | int |
| 31 | __lll_trylock_elision (int *futex, short *adapt_count) |
| 32 | { |
| 33 | /* Implement POSIX semantics by forbiding nesting elided trylocks. */ |
| 34 | __libc_tabort (_ABORT_NESTED_TRYLOCK); |
| 35 | |
| 36 | /* Only try a transaction if it's worth it. */ |
| 37 | if (atomic_load_relaxed (adapt_count) > 0) |
| 38 | { |
| 39 | goto use_lock; |
| 40 | } |
| 41 | |
| 42 | if (__libc_tbegin (0)) |
| 43 | { |
| 44 | if (*futex == 0) |
| 45 | return 0; |
| 46 | |
| 47 | /* Lock was busy. This is never a nested transaction. |
| 48 | End it, and set the adapt count. */ |
| 49 | __libc_tend (0); |
| 50 | |
| 51 | if (aconf.skip_lock_busy > 0) |
| 52 | atomic_store_relaxed (adapt_count, aconf.skip_lock_busy); |
| 53 | } |
| 54 | else |
| 55 | { |
| 56 | if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ())) |
| 57 | { |
| 58 | /* A persistent failure indicates that a retry will probably |
| 59 | result in another failure. Use normal locking now and |
| 60 | for the next couple of calls. */ |
| 61 | if (aconf.skip_trylock_internal_abort > 0) |
| 62 | atomic_store_relaxed (adapt_count, |
| 63 | aconf.skip_trylock_internal_abort); |
| 64 | } |
| 65 | } |
| 66 | |
| 67 | use_lock: |
| 68 | return lll_trylock (*futex); |
| 69 | } |
| 70 | libc_hidden_def (__lll_trylock_elision) |
| 71 |