libgomp/config/linux/bar.h

   1 /* Copyright (C) 2005-2023 Free Software Foundation, Inc.
   2    Contributed by Richard Henderson <rth@redhat.com>.
   3
   4    This file is part of the GNU Offloading and Multi Processing Library
   5    (libgomp).
   6
   7    Libgomp is free software; you can redistribute it and/or modify it
   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.
  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
  14    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  15    more details.
  16
  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/>.  */
  25
  26 /* This is a Linux specific implementation of a barrier synchronization
  27    mechanism for libgomp.  This type is private to the library.  This
  28    implementation uses atomic instructions and the futex syscall.  */
  29
  30 #ifndef GOMP_BARRIER_H
  31 #define GOMP_BARRIER_H 1
  32
  33 #include "mutex.h"
  34
  35 typedef struct
  36 {
  37   /* Make sure total/generation is in a mostly read cacheline, while
  38      awaited in a separate cacheline.  */
  39   unsigned total __attribute__((aligned (64)));
  40   unsigned generation;
  41   unsigned awaited __attribute__((aligned (64)));
  42   unsigned awaited_final;
  43 } gomp_barrier_t;
  44
  45 typedef unsigned int gomp_barrier_state_t;
  46
  47 /* The generation field contains a counter in the high bits, with a few
  48    low bits dedicated to flags.  Note that TASK_PENDING and WAS_LAST can
  49    share space because WAS_LAST is never stored back to generation.  */
  50 #define BAR_TASK_PENDING        1
  51 #define BAR_WAS_LAST            1
  52 #define BAR_WAITING_FOR_TASK    2
  53 #define BAR_CANCELLED           4
  54 #define BAR_INCR                8
  55
  56 static inline void gomp_barrier_init (gomp_barrier_t *bar, unsigned count)
  57 {
  58   bar->total = count;
  59   bar->awaited = count;
  60   bar->awaited_final = count;
  61   bar->generation = 0;
  62 }
  63
  64 static inline void gomp_barrier_reinit (gomp_barrier_t *bar, unsigned count)
  65 {
  66   __atomic_add_fetch (&bar->awaited, count - bar->total, MEMMODEL_ACQ_REL);
  67   bar->total = count;
  68 }
  69
  70 static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
  71 {
  72 }
  73
  74 extern void gomp_barrier_wait (gomp_barrier_t *);
  75 extern void gomp_barrier_wait_last (gomp_barrier_t *);
  76 extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
  77 extern void gomp_team_barrier_wait (gomp_barrier_t *);
  78 extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
  79 extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
  80                                         gomp_barrier_state_t);
  81 extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
  82 extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
  83                                                gomp_barrier_state_t);
  84 extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
  85 struct gomp_team;
  86 extern void gomp_team_barrier_cancel (struct gomp_team *);
  87
  88 static inline gomp_barrier_state_t
  89 gomp_barrier_wait_start (gomp_barrier_t *bar)
  90 {
  91   unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
  92   ret &= -BAR_INCR | BAR_CANCELLED;
  93   /* A memory barrier is needed before exiting from the various forms
  94      of gomp_barrier_wait, to satisfy OpenMP API version 3.1 section
  95      2.8.6 flush Construct, which says there is an implicit flush during
  96      a barrier region.  This is a convenient place to add the barrier,
  97      so we use MEMMODEL_ACQ_REL here rather than MEMMODEL_ACQUIRE.  */
  98   if (__atomic_add_fetch (&bar->awaited, -1, MEMMODEL_ACQ_REL) == 0)
  99     ret |= BAR_WAS_LAST;
 100   return ret;
 101 }
 102
 103 static inline gomp_barrier_state_t
 104 gomp_barrier_wait_cancel_start (gomp_barrier_t *bar)
 105 {
 106   return gomp_barrier_wait_start (bar);
 107 }
 108
 109 /* This is like gomp_barrier_wait_start, except it decrements
 110    bar->awaited_final rather than bar->awaited and should be used
 111    for the gomp_team_end barrier only.  */
 112 static inline gomp_barrier_state_t
 113 gomp_barrier_wait_final_start (gomp_barrier_t *bar)
 114 {
 115   unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
 116   ret &= -BAR_INCR | BAR_CANCELLED;
 117   /* See above gomp_barrier_wait_start comment.  */
 118   if (__atomic_add_fetch (&bar->awaited_final, -1, MEMMODEL_ACQ_REL) == 0)
 119     ret |= BAR_WAS_LAST;
 120   return ret;
 121 }
 122
 123 static inline bool
 124 gomp_barrier_last_thread (gomp_barrier_state_t state)
 125 {
 126   return state & BAR_WAS_LAST;
 127 }
 128
 129 /* All the inlines below must be called with team->task_lock
 130    held.  */
 131
 132 static inline void
 133 gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
 134 {
 135   bar->generation |= BAR_TASK_PENDING;
 136 }
 137
 138 static inline void
 139 gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
 140 {
 141   bar->generation &= ~BAR_TASK_PENDING;
 142 }
 143
 144 static inline void
 145 gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
 146 {
 147   bar->generation |= BAR_WAITING_FOR_TASK;
 148 }
 149
 150 static inline bool
 151 gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
 152 {
 153   return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
 154 }
 155
 156 static inline bool
 157 gomp_team_barrier_cancelled (gomp_barrier_t *bar)
 158 {
 159   return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
 160 }
 161
 162 static inline void
 163 gomp_team_barrier_done (gomp_barrier_t *bar, gomp_barrier_state_t state)
 164 {
 165   bar->generation = (state & -BAR_INCR) + BAR_INCR;
 166 }
 167
 168 #endif /* GOMP_BARRIER_H */