60 lines
2.0 KiB
C
60 lines
2.0 KiB
C
/* Concurrent allocation and initialization of a pointer.
|
|
Copyright (C) 2018-2022 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library 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
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
#include <allocate_once.h>
|
|
#include <stdlib.h>
|
|
#include <stdbool.h>
|
|
|
|
void *
|
|
__libc_allocate_once_slow (void **place, void *(*allocate) (void *closure),
|
|
void (*deallocate) (void *closure, void *ptr),
|
|
void *closure)
|
|
{
|
|
void *result = allocate (closure);
|
|
if (result == NULL)
|
|
return NULL;
|
|
|
|
/* This loop implements a strong CAS on *place, with acquire-release
|
|
MO semantics, from a weak CAS with relaxed-release MO. */
|
|
while (true)
|
|
{
|
|
/* Synchronizes with the acquire MO load in allocate_once. */
|
|
void *expected = NULL;
|
|
if (atomic_compare_exchange_weak_release (place, &expected, result))
|
|
return result;
|
|
|
|
/* The failed CAS has relaxed MO semantics, so perform another
|
|
acquire MO load. */
|
|
void *other_result = atomic_load_acquire (place);
|
|
if (other_result == NULL)
|
|
/* Spurious failure. Try again. */
|
|
continue;
|
|
|
|
/* We lost the race. Free what we allocated and return the
|
|
other result. */
|
|
if (deallocate == NULL)
|
|
free (result);
|
|
else
|
|
deallocate (closure, result);
|
|
return other_result;
|
|
}
|
|
|
|
return result;
|
|
}
|
|
libc_hidden_def (__libc_allocate_once_slow)
|