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/* elision-trylock.c: Lock eliding trylock for pthreads.
Copyright (C) 2015-2020 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 <pthread.h>
#include <pthreadP.h>
#include <lowlevellock.h>
#include <elision-conf.h>
#include "htm.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 elided trylocks. */
__libc_tabort (_ABORT_NESTED_TRYLOCK);
/* Only try a transaction if it's worth it. */
if (atomic_load_relaxed (adapt_count) > 0)
{
goto use_lock;
}
if (__libc_tbegin (0))
{
if (*futex == 0)
return 0;
/* Lock was busy. This is never a nested transaction.
End it, and set the adapt count. */
__libc_tend (0);
if (aconf.skip_lock_busy > 0)
atomic_store_relaxed (adapt_count, aconf.skip_lock_busy);
}
else
{
if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
{
/* 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 (aconf.skip_trylock_internal_abort > 0)
atomic_store_relaxed (adapt_count,
aconf.skip_trylock_internal_abort);
}
}
use_lock:
return lll_trylock (*futex);
}
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