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fbd26352 | 1 | /* Copyright (C) 2005-2019 Free Software Foundation, Inc. |
1e8e9920 | 2 | Contributed by Richard Henderson <rth@redhat.com>. |
3 | ||
c35c9a62 | 4 | This file is part of the GNU Offloading and Multi Processing Library |
5 | (libgomp). | |
1e8e9920 | 6 | |
7 | Libgomp is free software; you can redistribute it and/or modify it | |
6bc9506f | 8 | under the terms of the GNU General Public License as published by |
9 | the Free Software Foundation; either version 3, or (at your option) | |
10 | any later version. | |
1e8e9920 | 11 | |
12 | Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY | |
13 | WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS | |
6bc9506f | 14 | FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
1e8e9920 | 15 | more details. |
16 | ||
6bc9506f | 17 | Under Section 7 of GPL version 3, you are granted additional |
18 | permissions described in the GCC Runtime Library Exception, version | |
19 | 3.1, as published by the Free Software Foundation. | |
20 | ||
21 | You should have received a copy of the GNU General Public License and | |
22 | a copy of the GCC Runtime Library Exception along with this program; | |
23 | see the files COPYING3 and COPYING.RUNTIME respectively. If not, see | |
24 | <http://www.gnu.org/licenses/>. */ | |
1e8e9920 | 25 | |
26 | /* This is a Linux specific implementation of a mutex synchronization | |
27 | mechanism for libgomp. This type is private to the library. This | |
28 | implementation uses atomic instructions and the futex syscall. */ | |
29 | ||
fd6481cf | 30 | #include "wait.h" |
1e8e9920 | 31 | |
11d92d93 | 32 | int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG; |
33 | int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG; | |
1e8e9920 | 34 | |
35 | void | |
4dcd09ad | 36 | gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval) |
1e8e9920 | 37 | { |
a28ddb67 | 38 | /* First loop spins a while. */ |
4dcd09ad | 39 | while (oldval == 1) |
1e8e9920 | 40 | { |
4dcd09ad | 41 | if (do_spin (mutex, 1)) |
42 | { | |
a28ddb67 | 43 | /* Spin timeout, nothing changed. Set waiting flag. */ |
44 | oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE); | |
4dcd09ad | 45 | if (oldval == 0) |
46 | return; | |
a28ddb67 | 47 | futex_wait (mutex, -1); |
4dcd09ad | 48 | break; |
49 | } | |
50 | else | |
51 | { | |
a28ddb67 | 52 | /* Something changed. If now unlocked, we're good to go. */ |
53 | oldval = 0; | |
54 | if (__atomic_compare_exchange_n (mutex, &oldval, 1, false, | |
55 | MEMMODEL_ACQUIRE, MEMMODEL_RELAXED)) | |
4dcd09ad | 56 | return; |
57 | } | |
1e8e9920 | 58 | } |
a28ddb67 | 59 | |
60 | /* Second loop waits until mutex is unlocked. We always exit this | |
61 | loop with wait flag set, so next unlock will awaken a thread. */ | |
62 | while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE))) | |
63 | do_wait (mutex, -1); | |
1e8e9920 | 64 | } |
65 | ||
66 | void | |
67 | gomp_mutex_unlock_slow (gomp_mutex_t *mutex) | |
68 | { | |
69 | futex_wake (mutex, 1); | |
70 | } |