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1 /* Copyright (C) 2005-2020 Free Software Foundation, Inc.
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2 Contributed by Richard Henderson <rth@redhat.com>.
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3
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111
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4 This file is part of the GNU Offloading and Multi Processing Library
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5 (libgomp).
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6
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7 Libgomp is free software; you can redistribute it and/or modify it
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8 under the terms of the GNU General Public License as published by
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9 the Free Software Foundation; either version 3, or (at your option)
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10 any later version.
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11
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12 Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
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13 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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14 FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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15 more details.
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16
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17 Under Section 7 of GPL version 3, you are granted additional
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18 permissions described in the GCC Runtime Library Exception, version
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19 3.1, as published by the Free Software Foundation.
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20
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21 You should have received a copy of the GNU General Public License and
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22 a copy of the GCC Runtime Library Exception along with this program;
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23 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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24 <http://www.gnu.org/licenses/>. */
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25
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26 /* This is a Linux specific implementation of a mutex synchronization
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27 mechanism for libgomp. This type is private to the library. This
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28 implementation uses atomic instructions and the futex syscall. */
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29
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30 #include "wait.h"
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31
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32 int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG;
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33 int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG;
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0
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34
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35 void
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36 gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval)
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37 {
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38 /* First loop spins a while. */
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39 while (oldval == 1)
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0
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40 {
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41 if (do_spin (mutex, 1))
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42 {
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43 /* Spin timeout, nothing changed. Set waiting flag. */
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44 oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE);
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45 if (oldval == 0)
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46 return;
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47 futex_wait (mutex, -1);
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48 break;
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49 }
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50 else
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51 {
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52 /* Something changed. If now unlocked, we're good to go. */
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53 oldval = 0;
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54 if (__atomic_compare_exchange_n (mutex, &oldval, 1, false,
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55 MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
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56 return;
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57 }
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0
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58 }
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111
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59
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60 /* Second loop waits until mutex is unlocked. We always exit this
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61 loop with wait flag set, so next unlock will awaken a thread. */
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62 while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE)))
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63 do_wait (mutex, -1);
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64 }
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65
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66 void
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67 gomp_mutex_unlock_slow (gomp_mutex_t *mutex)
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68 {
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69 futex_wake (mutex, 1);
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70 }
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