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/* elision-lock.c: Elided pthread mutex lock.
Copyright (C) 2011-2016 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 <pthread.h>
#include "pthreadP.h"
#include "lowlevellock.h"
#include "hle.h"
#include <elision-conf.h>
#if !defined(LLL_LOCK) && !defined(EXTRAARG)
/* Make sure the configuration code is always linked in for static
libraries. */
#include "elision-conf.c"
#endif
#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 *futex, short *adapt_count, EXTRAARG int private)
{
if (*adapt_count <= 0)
{
unsigned status;
int try_xbegin;
for (try_xbegin = aconf.retry_try_xbegin;
try_xbegin > 0;
try_xbegin--)
{
if ((status = _xbegin()) == _XBEGIN_STARTED)
{
if (*futex == 0)
return 0;
/* Lock was busy. Fall back to normal locking.
Could also _xend here but xabort with 0xff code
is more visible in the profiler. */
_xabort (_ABORT_LOCK_BUSY);
}
if (!(status & _XABORT_RETRY))
{
if ((status & _XABORT_EXPLICIT)
&& _XABORT_CODE (status) == _ABORT_LOCK_BUSY)
{
/* Right now we skip here. Better would be to wait a bit
and retry. This likely needs some spinning. */
if (*adapt_count != aconf.skip_lock_busy)
*adapt_count = aconf.skip_lock_busy;
}
/* Internal abort. There is no chance for retry.
Use the normal locking and next time use lock.
Be careful to avoid writing to the lock. */
else if (*adapt_count != aconf.skip_lock_internal_abort)
*adapt_count = aconf.skip_lock_internal_abort;
break;
}
}
}
else
{
/* Use a normal lock until the threshold counter runs out.
Lost updates possible. */
(*adapt_count)--;
}
/* Use a normal lock here. */
return LLL_LOCK ((*futex), private);
}
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