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/* Copyright (C) 2011-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Chris Metcalf <cmetcalf@tilera.com>, 2011.
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"
#include <arch/spr_def.h>
#include <atomic.h>
/* Bound point for bounded exponential backoff */
#define BACKOFF_MAX 2048
/* Initial cycle delay for exponential backoff */
#define BACKOFF_START 32
/* Use cmpexch() after the initial fast-path exch to avoid
invalidating the cache line of the lock holder. */
#define TNS(p) atomic_exchange_acq((p), 1)
#define CMPTNS(p) atomic_compare_and_exchange_val_acq((p), 1, 0)
int
pthread_spin_lock (pthread_spinlock_t *lock)
{
if (__builtin_expect (TNS (lock) != 0, 0))
{
unsigned int backoff = BACKOFF_START;
while (CMPTNS (lock) != 0)
{
unsigned int start = __insn_mfspr (SPR_CYCLE);
while (__insn_mfspr (SPR_CYCLE) - start < backoff)
;
if (backoff < BACKOFF_MAX)
backoff *= 2;
}
}
return 0;
}
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