1 /* elision-lock.c: Elided pthread mutex lock.
2 Copyright (C) 2015-2019 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
22 #include <lowlevellock.h>
23 #include <elision-conf.h>
26 #if !defined(LLL_LOCK) && !defined(EXTRAARG)
27 /* Make sure the configuration code is always linked in for static
29 #include "elision-conf.c"
36 # define LLL_LOCK(a,b) lll_lock(a,b), 0
39 #define aconf __elision_aconf
41 /* Adaptive lock using transactions.
42 By default the lock region is run as a transaction, and when it
43 aborts or the lock is busy the lock adapts itself. */
46 __lll_lock_elision (int *lock, short *adapt_count, EXTRAARG int pshared)
48 /* adapt_count is accessed concurrently but is just a hint. Thus,
49 use atomic accesses but relaxed MO is sufficient. */
50 if (atomic_load_relaxed (adapt_count) > 0)
55 for (int i = aconf.try_tbegin; i > 0; i--)
57 if (__libc_tbegin (0))
61 /* Lock was busy. Fall back to normal locking. */
62 __libc_tabort (_ABORT_LOCK_BUSY);
66 /* A persistent failure indicates that a retry will probably
67 result in another failure. Use normal locking now and
68 for the next couple of calls. */
69 if (_TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
71 if (aconf.skip_lock_internal_abort > 0)
72 atomic_store_relaxed (adapt_count,
73 aconf.skip_lock_internal_abort);
79 /* Fall back to locks for a bit if retries have been exhausted */
80 if (aconf.try_tbegin > 0 && aconf.skip_lock_out_of_tbegin_retries > 0)
81 atomic_store_relaxed (adapt_count,
82 aconf.skip_lock_out_of_tbegin_retries);
85 return LLL_LOCK ((*lock), pshared);