60 lines
2.0 KiB
C
60 lines
2.0 KiB
C
/* Concurrent allocation and initialization of a pointer.
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Copyright (C) 2018-2019 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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<http://www.gnu.org/licenses/>. */
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#include <allocate_once.h>
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#include <stdlib.h>
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#include <stdbool.h>
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void *
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__libc_allocate_once_slow (void **place, void *(*allocate) (void *closure),
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void (*deallocate) (void *closure, void *ptr),
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void *closure)
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{
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void *result = allocate (closure);
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if (result == NULL)
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return NULL;
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/* This loop implements a strong CAS on *place, with acquire-release
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MO semantics, from a weak CAS with relaxed-release MO. */
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while (true)
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{
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/* Synchronizes with the acquire MO load in allocate_once. */
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void *expected = NULL;
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if (atomic_compare_exchange_ptr_weak_release (place, &expected, result))
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return result;
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/* The failed CAS has relaxed MO semantics, so perform another
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acquire MO load. */
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void *other_result = atomic_load_ptr_acquire (place);
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if (other_result == NULL)
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/* Spurious failure. Try again. */
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continue;
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/* We lost the race. Free what we allocated and return the
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other result. */
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if (deallocate == NULL)
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free (result);
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else
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deallocate (closure, result);
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return other_result;
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}
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return result;
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}
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libc_hidden_def (__libc_allocate_once_slow)
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