projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 5a414ff7 | 1 | /* Elided pthread mutex trylock. |
| b168057a | 2 | Copyright (C) 2014-2015 Free Software Foundation, Inc. |
| 5a414ff7 DV |
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 | ||
| 19 | #include <pthread.h> | |
| 20 | #include <pthreadP.h> | |
| 21 | #include <lowlevellock.h> | |
| 22 | #include <htmintrin.h> | |
| 23 | #include <elision-conf.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 | __asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t" | |
| 34 | ".machine \"all\"" | |
| 35 | : : : "memory"); | |
| 36 | ||
| 37 | /* Implement POSIX semantics by forbiding nesting elided trylocks. | |
| 38 | Sorry. After the abort the code is re-executed | |
| 39 | non transactional and if the lock was already locked | |
| 40 | return an error. */ | |
| 41 | if (__builtin_tx_nesting_depth () > 0) | |
| 42 | { | |
| 43 | /* Note that this abort may terminate an outermost transaction that | |
| 44 | was created outside glibc. | |
| 45 | This persistently aborts the current transactions to force | |
| 46 | them to use the default lock instead of retrying transactions | |
| 47 | until their try_tbegin is zero. | |
| 48 | */ | |
| 49 | __builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1); | |
| 50 | } | |
| 51 | ||
| 52 | /* Only try a transaction if it's worth it. */ | |
| 53 | if (*adapt_count <= 0) | |
| 54 | { | |
| 55 | unsigned status; | |
| 56 | ||
| 57 | if (__builtin_expect | |
| 58 | ((status = __builtin_tbegin ((void *)0)) == _HTM_TBEGIN_STARTED, 1)) | |
| 59 | { | |
| 60 | if (*futex == 0) | |
| 61 | return 0; | |
| 62 | /* Lock was busy. Fall back to normal locking. */ | |
| 63 | /* Since we are in a non-nested transaction there is no need to abort, | |
| 64 | which is expensive. */ | |
| 65 | __builtin_tend (); | |
| 66 | /* Note: Changing the adapt_count here might abort a transaction on a | |
| 67 | different cpu, but that could happen anyway when the futex is | |
| 68 | acquired, so there's no need to check the nesting depth here. */ | |
| 69 | if (aconf.skip_lock_busy > 0) | |
| 70 | *adapt_count = aconf.skip_lock_busy; | |
| 71 | } | |
| 72 | else | |
| 73 | { | |
| 74 | if (status != _HTM_TBEGIN_TRANSIENT) | |
| 75 | { | |
| 76 | /* A persistent abort (cc 1 or 3) indicates that a retry is | |
| 77 | probably futile. Use the normal locking now and for the | |
| 78 | next couple of calls. | |
| 79 | Be careful to avoid writing to the lock. */ | |
| 80 | if (aconf.skip_trylock_internal_abort > 0) | |
| 81 | *adapt_count = aconf.skip_trylock_internal_abort; | |
| 82 | } | |
| 83 | } | |
| 84 | /* Could do some retries here. */ | |
| 85 | } | |
| 86 | else | |
| 87 | { | |
| 88 | /* Lost updates are possible, but harmless. Due to races this might lead | |
| 89 | to *adapt_count becoming less than zero. */ | |
| 90 | (*adapt_count)--; | |
| 91 | } | |
| 92 | ||
| 93 | return lll_trylock (*futex); | |
| 94 | } |