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30891f35fa
We stopped adding "Contributed by" or similar lines in sources in 2012 in favour of git logs and keeping the Contributors section of the glibc manual up to date. Removing these lines makes the license header a bit more consistent across files and also removes the possibility of error in attribution when license blocks or files are copied across since the contributed-by lines don't actually reflect reality in those cases. Move all "Contributed by" and similar lines (Written by, Test by, etc.) into a new file CONTRIBUTED-BY to retain record of these contributions. These contributors are also mentioned in manual/contrib.texi, so we just maintain this additional record as a courtesy to the earlier developers. The following scripts were used to filter a list of files to edit in place and to clean up the CONTRIBUTED-BY file respectively. These were not added to the glibc sources because they're not expected to be of any use in future given that this is a one time task: https://gist.github.com/siddhesh/b5ecac94eabfd72ed2916d6d8157e7dc https://gist.github.com/siddhesh/15ea1f5e435ace9774f485030695ee02 Reviewed-by: Carlos O'Donell <carlos@redhat.com>
101 lines
3.2 KiB
C
101 lines
3.2 KiB
C
/* sem_post -- post to a POSIX semaphore. Generic futex-using version.
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Copyright (C) 2003-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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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<https://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_34);
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#if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
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compat_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
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#endif
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#if OTHER_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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unsigned int *futex = (unsigned 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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futex_wake (futex, 1, LLL_SHARED);
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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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