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https://github.com/jart/cosmopolitan.git
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61 lines
3 KiB
C
61 lines
3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 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/dce.h"
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#include "libc/intrin/atomic.h"
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#include "libc/intrin/futex.internal.h"
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#include "libc/intrin/pthread.h"
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static int pthread_rwlock_rdlock_spin(pthread_rwlock_t *rwlock, int expect,
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int tries) {
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if (tries < 7) {
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volatile int i;
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for (i = 0; i != 1 << tries; i++) {
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}
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tries++;
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} else if (IsLinux() || IsOpenbsd()) {
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atomic_fetch_add(&rwlock->waits, 1);
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_futex_wait_private(&rwlock->lock, expect, &(struct timespec){1});
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atomic_fetch_sub(&rwlock->waits, 1);
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} else {
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pthread_yield();
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}
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return tries;
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}
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/**
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* Acquires read lock on read-write lock.
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*
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* @return 0 on success, or errno on error
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*/
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int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock) {
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int old, tries;
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for (tries = 0;;) {
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old = atomic_load_explicit(&rwlock->lock, memory_order_relaxed);
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if (old >= 0) {
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do {
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if (atomic_compare_exchange_weak_explicit(&rwlock->lock, &old, old + 1,
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memory_order_acquire,
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memory_order_relaxed)) {
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return 0;
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}
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} while (old >= 0);
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}
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tries = pthread_rwlock_rdlock_spin(rwlock, old, tries);
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}
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}
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