glibc/nptl/sem_post.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

101 lines
3.2 KiB
C

/* sem_post -- post to a POSIX semaphore. Generic futex-using version.
Copyright (C) 2003-2022 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 <atomic.h>
#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h> /* lll_futex* used by the old code. */
#include <futex-internal.h>
#include <internaltypes.h>
#include <semaphore.h>
#include <shlib-compat.h>
/* See sem_wait for an explanation of the algorithm. */
int
__new_sem_post (sem_t *sem)
{
struct new_sem *isem = (struct new_sem *) sem;
int private = isem->private;
#if __HAVE_64B_ATOMICS
/* Add a token to the semaphore. We use release MO to make sure that a
thread acquiring this token synchronizes with us and other threads that
added tokens before (the release sequence includes atomic RMW operations
by other threads). */
/* TODO Use atomic_fetch_add to make it scale better than a CAS loop? */
uint64_t d = atomic_load_relaxed (&isem->data);
do
{
if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX)
{
__set_errno (EOVERFLOW);
return -1;
}
}
while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1));
/* If there is any potentially blocked waiter, wake one of them. */
if ((d >> SEM_NWAITERS_SHIFT) > 0)
futex_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, 1, private);
#else
/* Add a token to the semaphore. Similar to 64b version. */
unsigned int v = atomic_load_relaxed (&isem->value);
do
{
if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX)
{
__set_errno (EOVERFLOW);
return -1;
}
}
while (!atomic_compare_exchange_weak_release
(&isem->value, &v, v + (1 << SEM_VALUE_SHIFT)));
/* If there is any potentially blocked waiter, wake one of them. */
if ((v & SEM_NWAITERS_MASK) != 0)
futex_wake (&isem->value, 1, private);
#endif
return 0;
}
versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_34);
#if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
compat_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
#endif
#if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
int
attribute_compat_text_section
__old_sem_post (sem_t *sem)
{
unsigned int *futex = (unsigned int *) sem;
/* We must need to synchronize with consumers of this token, so the atomic
increment must have release MO semantics. */
atomic_write_barrier ();
(void) atomic_increment_val (futex);
/* We always have to assume it is a shared semaphore. */
futex_wake (futex, 1, LLL_SHARED);
return 0;
}
compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
#endif