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/* Copyright (C) 2012-2022 Free Software Foundation, Inc.
Contributed by Richard Henderson <rth@redhat.com>.
This file is part of the GNU Atomic Library (libatomic).
Libatomic 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 of the License, or
(at your option) any later version.
Libatomic 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/>. */
#include "libatomic_i.h"
#include <pthread.h>
/* The target page size. Must be no larger than the runtime page size,
lest locking fail with virtual address aliasing (i.e. a page mmaped
at two locations). */
#ifndef PAGE_SIZE
#define PAGE_SIZE 4096
#endif
/* The target cacheline size. This is an optimization; the padding that
should be applied to the locks to keep them from interfering. */
#ifndef CACHLINE_SIZE
#define CACHLINE_SIZE 64
#endif
/* The granularity at which locks are applied. Almost certainly the
cachline size is the right thing to use here. */
#ifndef WATCH_SIZE
#define WATCH_SIZE CACHLINE_SIZE
#endif
struct lock
{
pthread_mutex_t mutex;
char pad[sizeof(pthread_mutex_t) < CACHLINE_SIZE
? CACHLINE_SIZE - sizeof(pthread_mutex_t)
: 0];
};
#define NLOCKS (PAGE_SIZE / WATCH_SIZE)
static struct lock locks[NLOCKS] = {
[0 ... NLOCKS-1].mutex = PTHREAD_MUTEX_INITIALIZER
};
static inline uintptr_t
addr_hash (void *ptr)
{
return ((uintptr_t)ptr / WATCH_SIZE) % NLOCKS;
}
void
libat_lock_1 (void *ptr)
{
pthread_mutex_lock (&locks[addr_hash (ptr)].mutex);
}
void
libat_unlock_1 (void *ptr)
{
pthread_mutex_unlock (&locks[addr_hash (ptr)].mutex);
}
void
libat_lock_n (void *ptr, size_t n)
{
uintptr_t h = addr_hash (ptr);
size_t i = 0;
/* Don't lock more than all the locks we have. */
if (n > PAGE_SIZE)
n = PAGE_SIZE;
do
{
pthread_mutex_lock (&locks[h].mutex);
if (++h == NLOCKS)
h = 0;
i += WATCH_SIZE;
}
while (i < n);
}
void
libat_unlock_n (void *ptr, size_t n)
{
uintptr_t h = addr_hash (ptr);
size_t i = 0;
if (n > PAGE_SIZE)
n = PAGE_SIZE;
do
{
pthread_mutex_unlock (&locks[h].mutex);
if (++h == NLOCKS)
h = 0;
i += WATCH_SIZE;
}
while (i < n);
}
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