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1 /* Copyright (C) 2005-2017 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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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 barrier 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 #ifndef GOMP_BARRIER_H
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31 #define GOMP_BARRIER_H 1
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32
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33 #include "mutex.h"
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34
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35 typedef struct
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36 {
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37 /* Make sure total/generation is in a mostly read cacheline, while
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38 awaited in a separate cacheline. */
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39 unsigned total __attribute__((aligned (64)));
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40 unsigned generation;
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41 unsigned awaited __attribute__((aligned (64)));
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42 unsigned awaited_final;
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43 } gomp_barrier_t;
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44
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45 typedef unsigned int gomp_barrier_state_t;
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46
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47 /* The generation field contains a counter in the high bits, with a few
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48 low bits dedicated to flags. Note that TASK_PENDING and WAS_LAST can
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49 share space because WAS_LAST is never stored back to generation. */
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50 #define BAR_TASK_PENDING 1
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51 #define BAR_WAS_LAST 1
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52 #define BAR_WAITING_FOR_TASK 2
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53 #define BAR_CANCELLED 4
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54 #define BAR_INCR 8
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55
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56 static inline void gomp_barrier_init (gomp_barrier_t *bar, unsigned count)
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57 {
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58 bar->total = count;
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59 bar->awaited = count;
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60 bar->awaited_final = count;
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61 bar->generation = 0;
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62 }
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63
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64 static inline void gomp_barrier_reinit (gomp_barrier_t *bar, unsigned count)
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65 {
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66 __atomic_add_fetch (&bar->awaited, count - bar->total, MEMMODEL_ACQ_REL);
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67 bar->total = count;
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68 }
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69
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70 static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
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71 {
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72 }
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73
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74 extern void gomp_barrier_wait (gomp_barrier_t *);
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75 extern void gomp_barrier_wait_last (gomp_barrier_t *);
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76 extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
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77 extern void gomp_team_barrier_wait (gomp_barrier_t *);
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78 extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
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79 extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
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80 gomp_barrier_state_t);
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81 extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
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82 extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
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83 gomp_barrier_state_t);
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84 extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
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85 struct gomp_team;
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86 extern void gomp_team_barrier_cancel (struct gomp_team *);
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87
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88 static inline gomp_barrier_state_t
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89 gomp_barrier_wait_start (gomp_barrier_t *bar)
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90 {
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91 unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
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92 ret &= -BAR_INCR | BAR_CANCELLED;
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93 /* A memory barrier is needed before exiting from the various forms
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94 of gomp_barrier_wait, to satisfy OpenMP API version 3.1 section
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95 2.8.6 flush Construct, which says there is an implicit flush during
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96 a barrier region. This is a convenient place to add the barrier,
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97 so we use MEMMODEL_ACQ_REL here rather than MEMMODEL_ACQUIRE. */
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98 if (__atomic_add_fetch (&bar->awaited, -1, MEMMODEL_ACQ_REL) == 0)
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99 ret |= BAR_WAS_LAST;
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100 return ret;
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101 }
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102
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103 static inline gomp_barrier_state_t
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104 gomp_barrier_wait_cancel_start (gomp_barrier_t *bar)
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105 {
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106 return gomp_barrier_wait_start (bar);
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107 }
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108
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109 /* This is like gomp_barrier_wait_start, except it decrements
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110 bar->awaited_final rather than bar->awaited and should be used
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111 for the gomp_team_end barrier only. */
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112 static inline gomp_barrier_state_t
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113 gomp_barrier_wait_final_start (gomp_barrier_t *bar)
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114 {
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115 unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
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116 ret &= -BAR_INCR | BAR_CANCELLED;
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117 /* See above gomp_barrier_wait_start comment. */
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118 if (__atomic_add_fetch (&bar->awaited_final, -1, MEMMODEL_ACQ_REL) == 0)
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119 ret |= BAR_WAS_LAST;
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120 return ret;
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121 }
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122
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123 static inline bool
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124 gomp_barrier_last_thread (gomp_barrier_state_t state)
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125 {
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126 return state & BAR_WAS_LAST;
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127 }
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128
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129 /* All the inlines below must be called with team->task_lock
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130 held. */
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131
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132 static inline void
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133 gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
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134 {
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135 bar->generation |= BAR_TASK_PENDING;
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136 }
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137
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138 static inline void
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139 gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
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140 {
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141 bar->generation &= ~BAR_TASK_PENDING;
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142 }
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143
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144 static inline void
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145 gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
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146 {
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147 bar->generation |= BAR_WAITING_FOR_TASK;
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148 }
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149
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150 static inline bool
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151 gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
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152 {
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153 return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
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154 }
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155
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156 static inline bool
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157 gomp_team_barrier_cancelled (gomp_barrier_t *bar)
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158 {
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159 return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
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160 }
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161
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162 static inline void
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163 gomp_team_barrier_done (gomp_barrier_t *bar, gomp_barrier_state_t state)
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164 {
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165 bar->generation = (state & -BAR_INCR) + BAR_INCR;
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166 }
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167
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168 #endif /* GOMP_BARRIER_H */
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