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70 lines
2.1 KiB
C
70 lines
2.1 KiB
C
/* elision-trylock.c: Lock eliding trylock for pthreads.
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Copyright (C) 2015-2020 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 <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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#define aconf __elision_aconf
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/* Try to elide a futex trylock. FUTEX is the futex variable. ADAPT_COUNT is
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the adaptation counter in the mutex. */
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int
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__lll_trylock_elision (int *futex, short *adapt_count)
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{
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/* Implement POSIX semantics by forbiding nesting elided trylocks. */
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__libc_tabort (_ABORT_NESTED_TRYLOCK);
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/* Only try a transaction if it's worth it. */
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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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if (__libc_tbegin (0))
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{
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if (*futex == 0)
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return 0;
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/* Lock was busy. This is never a nested transaction.
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End it, and set the adapt count. */
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__libc_tend (0);
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if (aconf.skip_lock_busy > 0)
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atomic_store_relaxed (adapt_count, aconf.skip_lock_busy);
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}
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else
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{
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if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
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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 (aconf.skip_trylock_internal_abort > 0)
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atomic_store_relaxed (adapt_count,
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aconf.skip_trylock_internal_abort);
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}
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}
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use_lock:
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return lll_trylock (*futex);
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}
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