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042e1521c7
This commit fixes semaphore destruction by either using 64b atomic operations (where available), or by using two separate fields when only 32b atomic operations are available. In the latter case, we keep a conservative estimate of whether there are any waiting threads in one bit of the field that counts the number of available tokens, thus allowing sem_post to atomically both add a token and determine whether it needs to call futex_wake. See: https://sourceware.org/ml/libc-alpha/2014-12/msg00155.html
99 lines
2.6 KiB
C
99 lines
2.6 KiB
C
/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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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 <errno.h>
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#include <semaphore.h>
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#include <shlib-compat.h>
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#include "semaphoreP.h"
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#include <kernel-features.h>
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/* Returns FUTEX_PRIVATE if pshared is zero and private futexes are supported;
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returns FUTEX_SHARED otherwise.
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TODO Remove when cleaning up the futex API throughout glibc. */
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static __always_inline int
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futex_private_if_supported (int pshared)
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{
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if (pshared != 0)
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return LLL_SHARED;
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#ifdef __ASSUME_PRIVATE_FUTEX
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return LLL_PRIVATE;
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#else
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return THREAD_GETMEM (THREAD_SELF, header.private_futex)
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^ FUTEX_PRIVATE_FLAG;
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#endif
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}
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int
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__new_sem_init (sem_t *sem, int pshared, unsigned int value)
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{
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/* Parameter sanity check. */
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if (__glibc_unlikely (value > SEM_VALUE_MAX))
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{
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__set_errno (EINVAL);
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return -1;
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}
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/* Map to the internal type. */
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struct new_sem *isem = (struct new_sem *) sem;
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/* Use the values the caller provided. */
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#if __HAVE_64B_ATOMICS
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isem->data = value;
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#else
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isem->value = value << SEM_VALUE_SHIFT;
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isem->nwaiters = 0;
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#endif
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isem->private = futex_private_if_supported (pshared);
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return 0;
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}
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versioned_symbol (libpthread, __new_sem_init, sem_init, 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_init (sem, pshared, value)
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sem_t *sem;
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int pshared;
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unsigned int value;
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{
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/* Parameter sanity check. */
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if (__glibc_unlikely (value > SEM_VALUE_MAX))
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{
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__set_errno (EINVAL);
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return -1;
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}
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/* Map to the internal type. */
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struct old_sem *isem = (struct old_sem *) sem;
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/* Use the value the user provided. */
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isem->value = value;
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/* We cannot store the PSHARED attribute. So we always use the
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operations needed for shared semaphores. */
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return 0;
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}
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compat_symbol (libpthread, __old_sem_init, sem_init, GLIBC_2_0);
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#endif
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