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90 lines
2.5 KiB
C
90 lines
2.5 KiB
C
/* Copyright (C) 2004-2014 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 License as
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published by the Free Software Foundation; either version 2.1 of the
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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 "pthreadP.h"
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#include <lowlevellock.h>
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unsigned long int __fork_generation attribute_hidden;
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static void
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clear_once_control (void *arg)
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{
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pthread_once_t *once_control = (pthread_once_t *) arg;
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*once_control = 0;
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lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
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}
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int
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__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
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{
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for (;;)
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{
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int oldval;
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int newval;
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/* Pseudo code:
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newval = __fork_generation | 1;
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oldval = *once_control;
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if ((oldval & 2) == 0)
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*once_control = newval;
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Do this atomically. */
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do
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{
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newval = __fork_generation | 1;
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oldval = *once_control;
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if (oldval & 2)
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break;
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} while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval);
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/* Check if the initializer has already been done. */
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if ((oldval & 2) != 0)
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return 0;
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/* Check if another thread already runs the initializer. */
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if ((oldval & 1) == 0)
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break;
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/* Check whether the initializer execution was interrupted by a fork. */
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if (oldval != newval)
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break;
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/* Same generation, some other thread was faster. Wait. */
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lll_futex_wait (once_control, oldval, LLL_PRIVATE);
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}
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/* This thread is the first here. Do the initialization.
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Register a cleanup handler so that in case the thread gets
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interrupted the initialization can be restarted. */
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pthread_cleanup_push (clear_once_control, once_control);
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init_routine ();
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pthread_cleanup_pop (0);
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/* Say that the initialisation is done. */
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*once_control = __fork_generation | 2;
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/* Wake up all other threads. */
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lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
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return 0;
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}
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weak_alias (__pthread_once, pthread_once)
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hidden_def (__pthread_once)
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