| /* elision-trylock.c: Lock eliding trylock for pthreads. |
| Copyright (C) 2015-2018 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include <pthread.h> |
| #include <pthreadP.h> |
| #include <lowlevellock.h> |
| #include <elision-conf.h> |
| #include "htm.h" |
| |
| #define aconf __elision_aconf |
| |
| /* Try to elide a futex trylock. FUTEX is the futex variable. ADAPT_COUNT is |
| the adaptation counter in the mutex. */ |
| |
| int |
| __lll_trylock_elision (int *futex, short *adapt_count) |
| { |
| #ifndef __SPE__ |
| /* Implement POSIX semantics by forbiding nesting elided trylocks. */ |
| __libc_tabort (_ABORT_NESTED_TRYLOCK); |
| |
| /* Only try a transaction if it's worth it. */ |
| if (atomic_load_relaxed (adapt_count) > 0) |
| { |
| goto use_lock; |
| } |
| |
| if (__libc_tbegin (0)) |
| { |
| if (*futex == 0) |
| return 0; |
| |
| /* Lock was busy. This is never a nested transaction. |
| End it, and set the adapt count. */ |
| __libc_tend (0); |
| |
| if (aconf.skip_lock_busy > 0) |
| atomic_store_relaxed (adapt_count, aconf.skip_lock_busy); |
| } |
| else |
| { |
| if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ())) |
| { |
| /* A persistent failure indicates that a retry will probably |
| result in another failure. Use normal locking now and |
| for the next couple of calls. */ |
| if (aconf.skip_trylock_internal_abort > 0) |
| atomic_store_relaxed (adapt_count, |
| aconf.skip_trylock_internal_abort); |
| } |
| } |
| |
| use_lock: |
| #endif |
| return lll_trylock (*futex); |
| } |