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https://github.com/jart/cosmopolitan.git
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2d43d400c6
Cosmo now has a non-nsync implementation of POSIX read-write locks. It's possible to call pthread_rwlockattr_setpshared in PTHREAD_PROCESS_SHARED mode. Furthermore, if cosmo is built with PTHREAD_USE_NSYNC set to zero, then Cosmo shouldn't use nsync at all. That's helpful if you want to not link any Apache 2.0 licensed code.
60 lines
2.9 KiB
C
60 lines
2.9 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/errno.h"
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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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* Unlocks read-write lock.
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*
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* @return 0 on success, or errno on error
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* @raise EINVAL if lock is in a bad state
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*/
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errno_t pthread_rwlock_unlock(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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if (rwlock->_iswrite) {
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rwlock->_iswrite = 0;
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nsync_mu_unlock((nsync_mu *)rwlock->_nsync);
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} else {
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nsync_mu_runlock((nsync_mu *)rwlock->_nsync);
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}
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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 word = atomic_load_explicit(&rwlock->_word, memory_order_relaxed);
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for (;;) {
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if (word & 1) {
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atomic_store_explicit(&rwlock->_word, 0, memory_order_release);
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return 0;
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} else if (word) {
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if (atomic_compare_exchange_weak_explicit(&rwlock->_word, &word, word - 2,
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memory_order_release,
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memory_order_relaxed))
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return 0;
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} else {
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return EPERM;
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}
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}
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}
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