mirror of git://sourceware.org/git/glibc.git
104 lines
3.2 KiB
C
104 lines
3.2 KiB
C
/* sem_post -- post to a POSIX semaphore. Generic futex-using version.
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Copyright (C) 2003-2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <atomic.h>
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#include <errno.h>
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#include <sysdep.h>
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#include <lowlevellock.h> /* lll_futex* used by the old code. */
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#include <futex-internal.h>
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#include <internaltypes.h>
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#include <semaphore.h>
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#include <shlib-compat.h>
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/* See sem_wait for an explanation of the algorithm. */
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int
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__new_sem_post (sem_t *sem)
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{
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struct new_sem *isem = (struct new_sem *) sem;
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int private = isem->private;
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#if __HAVE_64B_ATOMICS
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/* Add a token to the semaphore. We use release MO to make sure that a
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thread acquiring this token synchronizes with us and other threads that
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added tokens before (the release sequence includes atomic RMW operations
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by other threads). */
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/* TODO Use atomic_fetch_add to make it scale better than a CAS loop? */
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uint64_t d = atomic_load_relaxed (&isem->data);
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do
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{
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if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX)
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{
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__set_errno (EOVERFLOW);
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return -1;
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}
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}
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while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1));
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/* If there is any potentially blocked waiter, wake one of them. */
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if ((d >> SEM_NWAITERS_SHIFT) > 0)
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futex_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, 1, private);
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#else
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/* Add a token to the semaphore. Similar to 64b version. */
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unsigned int v = atomic_load_relaxed (&isem->value);
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do
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{
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if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX)
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{
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__set_errno (EOVERFLOW);
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return -1;
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}
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}
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while (!atomic_compare_exchange_weak_release
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(&isem->value, &v, v + (1 << SEM_VALUE_SHIFT)));
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/* If there is any potentially blocked waiter, wake one of them. */
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if ((v & SEM_NWAITERS_MASK) != 0)
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futex_wake (&isem->value, 1, private);
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#endif
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return 0;
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}
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versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
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#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
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int
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attribute_compat_text_section
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__old_sem_post (sem_t *sem)
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{
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int *futex = (int *) sem;
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/* We must need to synchronize with consumers of this token, so the atomic
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increment must have release MO semantics. */
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atomic_write_barrier ();
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(void) atomic_increment_val (futex);
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/* We always have to assume it is a shared semaphore. */
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int err = lll_futex_wake (futex, 1, LLL_SHARED);
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if (__builtin_expect (err, 0) < 0)
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{
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__set_errno (-err);
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return -1;
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}
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return 0;
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}
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compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
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#endif
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