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/* Copyright (C) 2005-2022 Free Software Foundation, Inc.
Contributed by Richard Henderson <rth@redhat.com>.
This file is part of the GNU Offloading and Multi Processing Library
(libgomp).
Libgomp is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
/* This is a Linux specific implementation of a barrier synchronization
mechanism for libgomp. This type is private to the library. This
implementation uses atomic instructions and the futex syscall. */
#ifndef GOMP_BARRIER_H
#define GOMP_BARRIER_H 1
#include "mutex.h"
typedef struct
{
/* Make sure total/generation is in a mostly read cacheline, while
awaited in a separate cacheline. */
unsigned total __attribute__((aligned (64)));
unsigned generation;
unsigned awaited __attribute__((aligned (64)));
unsigned awaited_final;
} gomp_barrier_t;
typedef unsigned int gomp_barrier_state_t;
/* The generation field contains a counter in the high bits, with a few
low bits dedicated to flags. Note that TASK_PENDING and WAS_LAST can
share space because WAS_LAST is never stored back to generation. */
#define BAR_TASK_PENDING 1
#define BAR_WAS_LAST 1
#define BAR_WAITING_FOR_TASK 2
#define BAR_CANCELLED 4
#define BAR_INCR 8
static inline void gomp_barrier_init (gomp_barrier_t *bar, unsigned count)
{
bar->total = count;
bar->awaited = count;
bar->awaited_final = count;
bar->generation = 0;
}
static inline void gomp_barrier_reinit (gomp_barrier_t *bar, unsigned count)
{
__atomic_add_fetch (&bar->awaited, count - bar->total, MEMMODEL_ACQ_REL);
bar->total = count;
}
static inline void gomp_barrier_destroy (gomp_barrier_t *bar)
{
}
extern void gomp_barrier_wait (gomp_barrier_t *);
extern void gomp_barrier_wait_last (gomp_barrier_t *);
extern void gomp_barrier_wait_end (gomp_barrier_t *, gomp_barrier_state_t);
extern void gomp_team_barrier_wait (gomp_barrier_t *);
extern void gomp_team_barrier_wait_final (gomp_barrier_t *);
extern void gomp_team_barrier_wait_end (gomp_barrier_t *,
gomp_barrier_state_t);
extern bool gomp_team_barrier_wait_cancel (gomp_barrier_t *);
extern bool gomp_team_barrier_wait_cancel_end (gomp_barrier_t *,
gomp_barrier_state_t);
extern void gomp_team_barrier_wake (gomp_barrier_t *, int);
struct gomp_team;
extern void gomp_team_barrier_cancel (struct gomp_team *);
static inline gomp_barrier_state_t
gomp_barrier_wait_start (gomp_barrier_t *bar)
{
unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
ret &= -BAR_INCR | BAR_CANCELLED;
/* A memory barrier is needed before exiting from the various forms
of gomp_barrier_wait, to satisfy OpenMP API version 3.1 section
2.8.6 flush Construct, which says there is an implicit flush during
a barrier region. This is a convenient place to add the barrier,
so we use MEMMODEL_ACQ_REL here rather than MEMMODEL_ACQUIRE. */
if (__atomic_add_fetch (&bar->awaited, -1, MEMMODEL_ACQ_REL) == 0)
ret |= BAR_WAS_LAST;
return ret;
}
static inline gomp_barrier_state_t
gomp_barrier_wait_cancel_start (gomp_barrier_t *bar)
{
return gomp_barrier_wait_start (bar);
}
/* This is like gomp_barrier_wait_start, except it decrements
bar->awaited_final rather than bar->awaited and should be used
for the gomp_team_end barrier only. */
static inline gomp_barrier_state_t
gomp_barrier_wait_final_start (gomp_barrier_t *bar)
{
unsigned int ret = __atomic_load_n (&bar->generation, MEMMODEL_ACQUIRE);
ret &= -BAR_INCR | BAR_CANCELLED;
/* See above gomp_barrier_wait_start comment. */
if (__atomic_add_fetch (&bar->awaited_final, -1, MEMMODEL_ACQ_REL) == 0)
ret |= BAR_WAS_LAST;
return ret;
}
static inline bool
gomp_barrier_last_thread (gomp_barrier_state_t state)
{
return state & BAR_WAS_LAST;
}
/* All the inlines below must be called with team->task_lock
held. */
static inline void
gomp_team_barrier_set_task_pending (gomp_barrier_t *bar)
{
bar->generation |= BAR_TASK_PENDING;
}
static inline void
gomp_team_barrier_clear_task_pending (gomp_barrier_t *bar)
{
bar->generation &= ~BAR_TASK_PENDING;
}
static inline void
gomp_team_barrier_set_waiting_for_tasks (gomp_barrier_t *bar)
{
bar->generation |= BAR_WAITING_FOR_TASK;
}
static inline bool
gomp_team_barrier_waiting_for_tasks (gomp_barrier_t *bar)
{
return (bar->generation & BAR_WAITING_FOR_TASK) != 0;
}
static inline bool
gomp_team_barrier_cancelled (gomp_barrier_t *bar)
{
return __builtin_expect ((bar->generation & BAR_CANCELLED) != 0, 0);
}
static inline void
gomp_team_barrier_done (gomp_barrier_t *bar, gomp_barrier_state_t state)
{
bar->generation = (state & -BAR_INCR) + BAR_INCR;
}
#endif /* GOMP_BARRIER_H */
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