85 lines
2.7 KiB
C
85 lines
2.7 KiB
C
/* 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 semaphore synchronization
|
|
mechanism for libgomp. This type is private to the library. This
|
|
implementation uses atomic instructions and the futex syscall. */
|
|
|
|
#include "wait.h"
|
|
|
|
void
|
|
gomp_sem_wait_slow (gomp_sem_t *sem, int count)
|
|
{
|
|
/* First loop spins a while. */
|
|
while (count == 0)
|
|
if (do_spin (sem, 0)
|
|
/* Spin timeout, nothing changed. Set waiting flag. */
|
|
&& __atomic_compare_exchange_n (sem, &count, SEM_WAIT, false,
|
|
MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
|
|
{
|
|
futex_wait (sem, SEM_WAIT);
|
|
count = *sem;
|
|
break;
|
|
}
|
|
/* Something changed. If it wasn't the wait flag, we're good to go. */
|
|
else if (__builtin_expect (((count = *sem) & SEM_WAIT) == 0 && count != 0,
|
|
1))
|
|
{
|
|
if (__atomic_compare_exchange_n (sem, &count, count - SEM_INC, false,
|
|
MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
|
|
return;
|
|
}
|
|
|
|
/* Second loop waits until semaphore is posted. We always exit this
|
|
loop with wait flag set, so next post will awaken a thread. */
|
|
while (1)
|
|
{
|
|
unsigned int wake = count & ~SEM_WAIT;
|
|
int newval = SEM_WAIT;
|
|
|
|
if (wake != 0)
|
|
newval |= wake - SEM_INC;
|
|
if (__atomic_compare_exchange_n (sem, &count, newval, false,
|
|
MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
|
|
{
|
|
if (wake != 0)
|
|
{
|
|
/* If we can wake more threads, do so now. */
|
|
if (wake > SEM_INC)
|
|
gomp_sem_post_slow (sem);
|
|
break;
|
|
}
|
|
do_wait (sem, SEM_WAIT);
|
|
count = *sem;
|
|
}
|
|
}
|
|
}
|
|
|
|
void
|
|
gomp_sem_post_slow (gomp_sem_t *sem)
|
|
{
|
|
futex_wake (sem, 1);
|
|
}
|