mirror of
https://github.com/jart/cosmopolitan.git
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65 lines
3.1 KiB
C
65 lines
3.1 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/atomic.h"
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#include "libc/cosmo.h"
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#include "libc/errno.h"
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#include "libc/intrin/atomic.h"
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#include "libc/thread/thread.h"
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#define INIT 0
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#define CALLING 1
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#define FINISHED 2
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/**
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* Ensures initialization function is called exactly once.
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*
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* This is the same as `pthread_once` except that it always uses a tiny
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* spinlock implementation and won't make any system calls. It's needed
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* since this function is an upstream dependency of both pthread_once()
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* and nsync_once(). Most code should favor calling those functions.
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*
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* @return 0 on success, or errno on error
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*/
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errno_t cosmo_once(atomic_uint *once, void init(void)) {
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uint32_t old;
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switch ((old = atomic_load_explicit(once, memory_order_acquire))) {
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case INIT:
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if (atomic_compare_exchange_strong_explicit(once, &old, CALLING,
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memory_order_acquire,
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memory_order_relaxed)) {
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init();
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atomic_store_explicit(once, FINISHED, memory_order_release);
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return 0;
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}
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// fallthrough
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case CALLING:
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for (;;) {
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if (atomic_load_explicit(once, memory_order_acquire) != CALLING) {
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break;
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}
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}
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return 0;
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case FINISHED:
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return 0;
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default:
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return EINVAL;
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}
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}
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__weak_reference(cosmo_once, call_once);
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