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The elision interfaces are closely aligned between the targets that implement them, so declare them in the generic <lowlevellock.h> file. Empty .c stubs are provided, so that fewer makefile updates under sysdeps are needed. Also simplify initialization via __libc_early_init. The symbols __lll_clocklock_elision, __lll_lock_elision, __lll_trylock_elision, __lll_unlock_elision, __pthread_force_elision move into libc. For the time being, non-hidden references are used from libpthread to access them, but once that part of libpthread is moved into libc, hidden symbols will be used again. (Hidden references seem desirable to reduce the likelihood of transactions aborts.)
82 lines
2.4 KiB
C
82 lines
2.4 KiB
C
/* elision-lock.c: Elided pthread mutex lock.
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Copyright (C) 2015-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <pthread.h>
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#include <pthreadP.h>
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#include <lowlevellock.h>
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#include <elision-conf.h>
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#include "htm.h"
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#ifndef EXTRAARG
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# define EXTRAARG
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#endif
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#ifndef LLL_LOCK
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# define LLL_LOCK(a,b) lll_lock(a,b), 0
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#endif
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#define aconf __elision_aconf
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/* Adaptive lock using transactions.
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By default the lock region is run as a transaction, and when it
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aborts or the lock is busy the lock adapts itself. */
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int
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__lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
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{
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/* adapt_count is accessed concurrently but is just a hint. Thus,
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use atomic accesses but relaxed MO is sufficient. */
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if (atomic_load_relaxed (adapt_count) > 0)
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{
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goto use_lock;
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}
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for (int i = aconf.try_tbegin; i > 0; i--)
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{
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if (__libc_tbegin (0))
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{
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if (*lock == 0)
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return 0;
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/* Lock was busy. Fall back to normal locking. */
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__libc_tabort (_ABORT_LOCK_BUSY);
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}
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else
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{
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/* A persistent failure indicates that a retry will probably
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result in another failure. Use normal locking now and
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for the next couple of calls. */
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if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
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{
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if (aconf.skip_lock_internal_abort > 0)
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atomic_store_relaxed (adapt_count,
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aconf.skip_lock_internal_abort);
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goto use_lock;
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}
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}
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}
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/* Fall back to locks for a bit if retries have been exhausted */
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if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
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atomic_store_relaxed (adapt_count,
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aconf.skip_lock_out_of_tbegin_retries);
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use_lock:
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return LLL_LOCK ((*lock), pshared);
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}
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libc_hidden_def (__lll_lock_elision)
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