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1 /*
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2 * Copyright (c) 2003, 2007-14 Matteo Frigo
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3 * Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology
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4 *
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5 * This program is free software; you can redistribute it and/or modify
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6 * it under the terms of the GNU General Public License as published by
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7 * the Free Software Foundation; either version 2 of the License, or
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8 * (at your option) any later version.
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9 *
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10 * This program is distributed in the hope that it will be useful,
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11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 * GNU General Public License for more details.
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14 *
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15 * You should have received a copy of the GNU General Public License
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16 * along with this program; if not, write to the Free Software
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17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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18 *
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19 */
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20
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21 /* openmp.c: thread spawning via OpenMP */
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22
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23 #include "threads.h"
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24
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25 #if !defined(_OPENMP)
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26 #error OpenMP enabled but not using an OpenMP compiler
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27 #endif
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28
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29 int X(ithreads_init)(void)
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30 {
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31 return 0; /* no error */
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32 }
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33
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34 /* Distribute a loop from 0 to loopmax-1 over nthreads threads.
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35 proc(d) is called to execute a block of iterations from d->min
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36 to d->max-1. d->thr_num indicate the number of the thread
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37 that is executing proc (from 0 to nthreads-1), and d->data is
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38 the same as the data parameter passed to X(spawn_loop).
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39
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40 This function returns only after all the threads have completed. */
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41 void X(spawn_loop)(int loopmax, int nthr, spawn_function proc, void *data)
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42 {
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43 int block_size;
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44 spawn_data d;
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45 int i;
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46
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47 A(loopmax >= 0);
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48 A(nthr > 0);
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49 A(proc);
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50
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51 if (!loopmax) return;
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52
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53 /* Choose the block size and number of threads in order to (1)
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54 minimize the critical path and (2) use the fewest threads that
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55 achieve the same critical path (to minimize overhead).
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56 e.g. if loopmax is 5 and nthr is 4, we should use only 3
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57 threads with block sizes of 2, 2, and 1. */
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58 block_size = (loopmax + nthr - 1) / nthr;
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59 nthr = (loopmax + block_size - 1) / block_size;
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60
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61 THREAD_ON; /* prevent debugging mode from failing under threads */
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62 #pragma omp parallel for private(d)
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63 for (i = 0; i < nthr; ++i) {
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64 d.max = (d.min = i * block_size) + block_size;
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65 if (d.max > loopmax)
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66 d.max = loopmax;
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67 d.thr_num = i;
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68 d.data = data;
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69 proc(&d);
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70 }
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71 THREAD_OFF; /* prevent debugging mode from failing under threads */
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72 }
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73
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74 void X(threads_cleanup)(void)
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75 {
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76 }
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77
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78 /* FIXME [Matteo Frigo 2015-05-25] What does "thread-safe"
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79 mean for openmp? */
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80 void X(threads_register_planner_hooks)(void)
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81 {
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82 }
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