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/* elision-lock.c: Elided pthread mutex lock.
Copyright (C) 2015-2022 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
<https://www.gnu.org/licenses/>. */
#include <stdio.h>
#include <pthread.h>
#include <pthreadP.h>
#include <lowlevellock.h>
#include <elision-conf.h>
#include "htm.h"
#ifndef EXTRAARG
# define EXTRAARG
#endif
#ifndef LLL_LOCK
# define LLL_LOCK(a,b) lll_lock(a,b), 0
#endif
#define aconf __elision_aconf
/* Adaptive lock using transactions.
By default the lock region is run as a transaction, and when it
aborts or the lock is busy the lock adapts itself. */
int
__lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
{
/* adapt_count is accessed concurrently but is just a hint. Thus,
use atomic accesses but relaxed MO is sufficient. */
if (atomic_load_relaxed (adapt_count) > 0)
{
goto use_lock;
}
for (int i = aconf.try_tbegin; i > 0; i--)
{
if (__libc_tbegin (0))
{
if (*lock == 0)
return 0;
/* Lock was busy. Fall back to normal locking. */
__libc_tabort (_ABORT_LOCK_BUSY);
}
else
{
/* 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 (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
{
if (aconf.skip_lock_internal_abort > 0)
atomic_store_relaxed (adapt_count,
aconf.skip_lock_internal_abort);
goto use_lock;
}
}
}
/* Fall back to locks for a bit if retries have been exhausted */
if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
atomic_store_relaxed (adapt_count,
aconf.skip_lock_out_of_tbegin_retries);
use_lock:
return LLL_LOCK ((*lock), pshared);
}
libc_hidden_def (__lll_lock_elision)
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