glibc/misc/allocate_once.c
Paul Eggert 581c785bf3 Update copyright dates with scripts/update-copyrights
I used these shell commands:

../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")

and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 7061 files FOO.

I then removed trailing white space from math/tgmath.h,
support/tst-support-open-dev-null-range.c, and
sysdeps/x86_64/multiarch/strlen-vec.S, to work around the following
obscure pre-commit check failure diagnostics from Savannah.  I don't
know why I run into these diagnostics whereas others evidently do not.

remote: *** 912-#endif
remote: *** 913:
remote: *** 914-
remote: *** error: lines with trailing whitespace found
...
remote: *** error: sysdeps/unix/sysv/linux/statx_cp.c: trailing lines
2022-01-01 11:40:24 -08:00

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)