libgomp/config/linux/bar.h

   1 /* Copyright (C) 2005-2013 Free Software Foundation, Inc.
   2    Contributed by Richard Henderson <rth@redhat.com>.
   3
   4    This file is part of the GNU OpenMP Library (libgomp).
   5
   6    Libgomp is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3, or (at your option)
   9    any later version.
  10
  11    Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
  12    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  13    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14    more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 /* This is a Linux specific implementation of a barrier synchronization
  26    mechanism for libgomp.  This type is private to the library.  This
  27    implementation uses atomic instructions and the futex syscall.  */
  28
  29 #ifndef GOMP_BARRIER_H
  30 #define GOMP_BARRIER_H 1
  31
  32 #include "mutex.h"
  33
  34 typedef struct
  35 {
  36   /* Make sure total/generation is in a mostly read cacheline, while
  37      awaited in a separate cacheline.  */
  38   unsigned total __attribute__((aligned (64)));
  39   unsigned generation;
  40   unsigned awaited __attribute__((aligned (64)));
  41   unsigned awaited_final;
  42 } gomp_barrier_t;
  43
  44 typedef unsigned int gomp_barrier_state_t;
  45
  46 /* The generation field contains a counter in the high bits, with a few
  47    low bits dedicated to flags.  Note that TASK_PENDING and WAS_LAST can
  48    share space because WAS_LAST is never stored back to generation.  */
  49 #define BAR_TASK_PENDING        1
  50 #define BAR_WAS_LAST            1
  51 #define BAR_WAITING_FOR_TASK    2
  52 #define BAR_CANCELLED           4
  53 #define BAR_INCR                8
  54
  55 static inline void gomp_barrier_init (gomp_barrier_t *bar, unsigned count)
  56 {
  57   bar->total = count;
  58   bar->awaited = count;
  59   bar->awaited_final = count;
  60   bar->generation = 0;
  61 }
  62
  63 static inline void gomp_barrier_reinit (gomp_barrier_t *bar, unsigned count)
  64 {
  65   __atomic_add_fetch (&bar->awaited, count - bar->total, MEMMODEL_ACQ_REL);
  66   bar->total = count;
  67 }
  68
  69 static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
  70 {
  71 }
  72
  73 extern void gomp_barrier_wait (gomp_barrier_t *);
  74 extern void gomp_barrier_wait_last (gomp_barrier_t *);
  75 extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
  76 extern void gomp_team_barrier_wait (gomp_barrier_t *);
  77 extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
  78 extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
  79                                         gomp_barrier_state_t);
  80 extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
  81 extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
  82                                                gomp_barrier_state_t);
  83 extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
  84 struct gomp_team;
  85 extern void gomp_team_barrier_cancel (struct gomp_team *);
  86
  87 static inline gomp_barrier_state_t
  88 gomp_barrier_wait_start (gomp_barrier_t *bar)
  89 {
  90   unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
  91   ret &= -BAR_INCR | BAR_CANCELLED;
  92   /* A memory barrier is needed before exiting from the various forms
  93      of gomp_barrier_wait, to satisfy OpenMP API version 3.1 section
  94      2.8.6 flush Construct, which says there is an implicit flush during
  95      a barrier region.  This is a convenient place to add the barrier,
  96      so we use MEMMODEL_ACQ_REL here rather than MEMMODEL_ACQUIRE.  */
  97   if (__atomic_add_fetch (&bar->awaited, -1, MEMMODEL_ACQ_REL) == 0)
  98     ret |= BAR_WAS_LAST;
  99   return ret;
 100 }
 101
 102 static inline gomp_barrier_state_t
 103 gomp_barrier_wait_cancel_start (gomp_barrier_t *bar)
 104 {
 105   return gomp_barrier_wait_start (bar);
 106 }
 107
 108 /* This is like gomp_barrier_wait_start, except it decrements
 109    bar->awaited_final rather than bar->awaited and should be used
 110    for the gomp_team_end barrier only.  */
 111 static inline gomp_barrier_state_t
 112 gomp_barrier_wait_final_start (gomp_barrier_t *bar)
 113 {
 114   unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
 115   ret &= -BAR_INCR | BAR_CANCELLED;
 116   /* See above gomp_barrier_wait_start comment.  */
 117   if (__atomic_add_fetch (&bar->awaited_final, -1, MEMMODEL_ACQ_REL) == 0)
 118     ret |= BAR_WAS_LAST;
 119   return ret;
 120 }
 121
 122 static inline bool
 123 gomp_barrier_last_thread (gomp_barrier_state_t state)
 124 {
 125   return state & BAR_WAS_LAST;
 126 }
 127
 128 /* All the inlines below must be called with team->task_lock
 129    held.  */
 130
 131 static inline void
 132 gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
 133 {
 134   bar->generation |= BAR_TASK_PENDING;
 135 }
 136
 137 static inline void
 138 gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
 139 {
 140   bar->generation &= ~BAR_TASK_PENDING;
 141 }
 142
 143 static inline void
 144 gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
 145 {
 146   bar->generation |= BAR_WAITING_FOR_TASK;
 147 }
 148
 149 static inline bool
 150 gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
 151 {
 152   return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
 153 }
 154
 155 static inline bool
 156 gomp_team_barrier_cancelled (gomp_barrier_t *bar)
 157 {
 158   return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
 159 }
 160
 161 static inline void
 162 gomp_team_barrier_done (gomp_barrier_t *bar, gomp_barrier_state_t state)
 163 {
 164   bar->generation = (state & -BAR_INCR) + BAR_INCR;
 165 }
 166
 167 #endif /* GOMP_BARRIER_H */