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51 lines
2.6 KiB
C
51 lines
2.6 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 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/intrin/atomic.h"
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#include "libc/thread/thread.h"
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#include "third_party/nsync/mu.h"
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/**
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* Acquires write 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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errno_t pthread_rwlock_wrlock(pthread_rwlock_t *rwlock) {
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#if PTHREAD_USE_NSYNC
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// use nsync if possible
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if (!rwlock->_pshared) {
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nsync_mu_lock((nsync_mu *)rwlock->_nsync);
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rwlock->_iswrite = 1;
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return 0;
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}
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#endif
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// naive implementation
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uint32_t w = 0;
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for (;;) {
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if (atomic_compare_exchange_weak_explicit(
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&rwlock->_word, &w, 1, memory_order_acquire, memory_order_relaxed))
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return 0;
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atomic_fetch_add(&rwlock->_waiters, 1);
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for (;;)
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if (!(w = atomic_load_explicit(&rwlock->_word, memory_order_relaxed)))
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break;
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atomic_fetch_sub(&rwlock->_waiters, 1);
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}
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}
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