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glibc/sysdeps/hppa/nptl/pthread_spin_init.c
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/* Copyright (C) 2006-2016 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; | |
} |