| /* Copyright (C) 2006-2018 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 "pthreadP.h" |
| |
| int |
| pthread_spin_init (pthread_spinlock_t *lock, int pshared) |
| { |
| /* CONCURRENCTY NOTES: |
| |
| The atomic_exchange_rel synchronizes-with the atomic_exhange_acq in |
| pthread_spin_lock. |
| |
| On hppa we must not use a plain `stw` to reset the guard lock. This |
| has to do with the kernel compare-and-swap helper that is used to |
| implement all of the atomic operations. |
| |
| The kernel CAS helper uses its own internal locks and that means that |
| to create a true happens-before relationship between any two threads, |
| the second thread must observe the internal lock having a value of 0 |
| (it must attempt to take the lock with ldcw). This creates the |
| ordering required for a second thread to observe the effects of the |
| RMW of the kernel CAS helper in any other thread. |
| |
| Therefore if a variable is used in an atomic macro it must always be |
| manipulated with atomic macros in order for memory ordering rules to |
| be preserved. */ |
| atomic_exchange_rel (lock, 0); |
| return 0; |
| } |
