/* elision-trylock.c: Lock eliding trylock for pthreads.

   Copyright (C) 2015-2018 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 <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)

{

#ifndef __SPE__

  /* 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:

#endif

  return lll_trylock (*futex);

}