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/* Copyright (C) 2004, 2005 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */ #include "pthreadP.h" #include <lowlevellock.h> unsigned long int __fork_generation attribute_hidden; static void clear_once_control (void *arg) { pthread_once_t *once_control = (pthread_once_t *) arg; *once_control = 0; lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); } int attribute_protected __pthread_once (pthread_once_t *once_control, void (*init_routine) (void)) { for (;;) { int oldval; int newval; /* Pseudo code: newval = __fork_generation | 1; oldval = *once_control; if ((oldval & 2) == 0) *once_control = newval; Do this atomically. */ do { newval = __fork_generation | 1; oldval = *once_control; if (oldval & 2) break; } while (atomic_compare_and_exchange_val_acq (once_control, newval, oldval) != oldval); /* Check if the initializer has already been done. */ if ((oldval & 2) != 0) return 0; /* Check if another thread already runs the initializer. */ if ((oldval & 1) == 0) break; /* Check whether the initializer execution was interrupted by a fork. */ if (oldval != newval) break; /* Same generation, some other thread was faster. Wait. */ lll_futex_wait (once_control, oldval, LLL_PRIVATE); } /* This thread is the first here. Do the initialization. Register a cleanup handler so that in case the thread gets interrupted the initialization can be restarted. */ pthread_cleanup_push (clear_once_control, once_control); init_routine (); pthread_cleanup_pop (0); /* Say that the initialisation is done. */ *once_control = __fork_generation | 2; /* Wake up all other threads. */ lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE); return 0; } weak_alias (__pthread_once, pthread_once) strong_alias (__pthread_once, __pthread_once_internal) #if defined(__USING_SJLJ_EXCEPTIONS__) && !defined(__PIC__) /* When statically linked, if pthread_create is used, this file will be brought in. The exception handling code in GCC assumes that if pthread_create is available, so are these. */ const void *include_pthread_getspecific attribute_hidden = pthread_getspecific; const void *include_pthread_setspecific attribute_hidden = pthread_setspecific; const void *include_pthread_key_create attribute_hidden = pthread_key_create; #endif |