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120 lines
3.6 KiB
C
120 lines
3.6 KiB
C
/* Elided pthread mutex lock.
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Copyright (C) 2014-2015 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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<http://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 <htmintrin.h>
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#include <elision-conf.h>
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#include <stdint.h>
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#if !defined(LLL_LOCK) && !defined(EXTRAARG)
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/* Make sure the configuration code is always linked in for static
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libraries. */
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#include "elision-conf.c"
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#endif
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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 *futex, short *adapt_count, EXTRAARG int private)
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{
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if (*adapt_count > 0)
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{
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/* Lost updates are possible, but harmless. Due to races this might lead
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to *adapt_count becoming less than zero. */
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(*adapt_count)--;
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goto use_lock;
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}
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__asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t"
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".machine \"all\""
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: : : "memory");
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int try_tbegin;
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for (try_tbegin = aconf.try_tbegin;
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try_tbegin > 0;
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try_tbegin--)
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{
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unsigned status;
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if (__builtin_expect
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((status = __builtin_tbegin((void *)0)) == _HTM_TBEGIN_STARTED, 1))
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{
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if (*futex == 0)
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return 0;
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/* Lock was busy. Fall back to normal locking. */
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if (__builtin_expect (__builtin_tx_nesting_depth (), 1))
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{
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/* In a non-nested transaction there is no need to abort,
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which is expensive. */
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__builtin_tend ();
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if (aconf.skip_lock_busy > 0)
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*adapt_count = aconf.skip_lock_busy;
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goto use_lock;
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}
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else /* nesting depth is > 1 */
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{
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/* A nested transaction will abort eventually because it
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cannot make any progress before *futex changes back to 0.
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So we may as well abort immediately.
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This persistently aborts the outer transaction to force
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the outer mutex use the default lock instead of retrying
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with transactions until the try_tbegin of the outer mutex
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is zero.
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The adapt_count of this inner mutex is not changed,
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because using the default lock with the inner mutex
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would abort the outer transaction.
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*/
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__builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1);
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}
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}
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else
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{
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if (status != _HTM_TBEGIN_TRANSIENT)
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{
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/* A persistent abort (cc 1 or 3) indicates that a retry is
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probably futile. Use the normal locking now and for the
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next couple of calls.
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Be careful to avoid writing to the lock. */
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if (aconf.skip_lock_internal_abort > 0)
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*adapt_count = 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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/* Same logic as above, but for for a number of temporary failures in a
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row. */
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if (aconf.skip_lock_out_of_tbegin_retries > 0 && aconf.try_tbegin > 0)
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*adapt_count = aconf.skip_lock_out_of_tbegin_retries;
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use_lock:
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return LLL_LOCK ((*futex), private);
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}
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