69 lines
2.0 KiB
C
69 lines
2.0 KiB
C
/* elision-trylock.c: Lock eliding trylock for pthreads.
|
|
Copyright (C) 2014 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)
|
|
{
|
|
/* Implement POSIX semantics by forbiding nesting elided trylocks. */
|
|
__builtin_tabort (_ABORT_NESTED_TRYLOCK);
|
|
|
|
/* Only try a transaction if it's worth it. */
|
|
if (*adapt_count > 0)
|
|
{
|
|
(*adapt_count)--;
|
|
goto use_lock;
|
|
}
|
|
|
|
if (__builtin_tbegin (0))
|
|
{
|
|
if (*futex == 0)
|
|
return 0;
|
|
|
|
/* Lock was busy. Fall back to normal locking. */
|
|
__builtin_tabort (_ABORT_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)
|
|
*adapt_count = aconf.skip_trylock_internal_abort;
|
|
}
|
|
|
|
if (aconf.skip_lock_busy > 0)
|
|
*adapt_count = aconf.skip_lock_busy;
|
|
}
|
|
|
|
use_lock:
|
|
return lll_trylock (*futex);
|
|
}
|