| /* elision-trylock.c: Lock eliding trylock for pthreads. |
| Copyright (C) 2013-2018 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 "hle.h" |
| #include <elision-conf.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) |
| { |
| /* Implement POSIX semantics by forbiding nesting |
| trylock. Sorry. After the abort the code is re-executed |
| non transactional and if the lock was already locked |
| return an error. */ |
| _xabort (_ABORT_NESTED_TRYLOCK); |
| |
| /* Only try a transaction if it's worth it. See __lll_lock_elision for |
| why we need atomic accesses. Relaxed MO is sufficient because this is |
| just a hint. */ |
| if (atomic_load_relaxed (adapt_count) <= 0) |
| { |
| unsigned status; |
| |
| if ((status = _xbegin()) == _XBEGIN_STARTED) |
| { |
| if (*futex == 0) |
| return 0; |
| |
| /* Lock was busy. Fall back to normal locking. |
| Could also _xend here but xabort with 0xff code |
| is more visible in the profiler. */ |
| _xabort (_ABORT_LOCK_BUSY); |
| } |
| |
| if (!(status & _XABORT_RETRY)) |
| { |
| /* Internal abort. No chance for retry. For future |
| locks don't try speculation for some time. See above for MO. */ |
| if (atomic_load_relaxed (adapt_count) |
| != aconf.skip_lock_internal_abort) |
| atomic_store_relaxed (adapt_count, aconf.skip_lock_internal_abort); |
| } |
| /* Could do some retries here. */ |
| } |
| else |
| { |
| /* Lost updates are possible but harmless (see above). */ |
| atomic_store_relaxed (adapt_count, |
| atomic_load_relaxed (adapt_count) - 1); |
| } |
| |
| return lll_trylock (*futex); |
| } |
