mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-27 07:20:11 +00:00
76 lines
2.5 KiB
C
76 lines
2.5 KiB
C
/* elision-trylock.c: Lock eliding trylock for pthreads.
|
|
Copyright (C) 2013-2020 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 "hle.h"
|
|
#include <elision-conf.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
|
|
trylock. Sorry. After the abort the code is re-executed
|
|
non transactional and if the lock was already locked
|
|
return an error. */
|
|
_xabort (_ABORT_NESTED_TRYLOCK);
|
|
|
|
/* Only try a transaction if it's worth it. See __lll_lock_elision for
|
|
why we need atomic accesses. Relaxed MO is sufficient because this is
|
|
just a hint. */
|
|
if (atomic_load_relaxed (adapt_count) <= 0)
|
|
{
|
|
unsigned status;
|
|
|
|
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))
|
|
{
|
|
/* Internal abort. No chance for retry. For future
|
|
locks don't try speculation for some time. See above for MO. */
|
|
if (atomic_load_relaxed (adapt_count)
|
|
!= aconf.skip_lock_internal_abort)
|
|
atomic_store_relaxed (adapt_count, aconf.skip_lock_internal_abort);
|
|
}
|
|
/* Could do some retries here. */
|
|
}
|
|
else
|
|
{
|
|
/* Lost updates are possible but harmless (see above). */
|
|
atomic_store_relaxed (adapt_count,
|
|
atomic_load_relaxed (adapt_count) - 1);
|
|
}
|
|
|
|
return lll_trylock (*futex);
|
|
}
|