mirror of
https://github.com/jart/cosmopolitan.git
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78 lines
3.5 KiB
C
78 lines
3.5 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/assert.h"
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#include "libc/calls/calls.h"
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#include "libc/errno.h"
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#include "libc/intrin/atomic.h"
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#include "libc/intrin/likely.h"
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#include "libc/intrin/weaken.h"
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#include "libc/thread/thread.h"
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#include "libc/thread/tls.h"
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#include "third_party/nsync/mu.h"
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/**
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* Locks mutex if it isn't locked already.
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*
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* Unlike pthread_mutex_lock() this function won't block and instead
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* returns an error immediately if the lock couldn't be acquired.
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*
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* @return 0 on success, or errno on error
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* @raise EBUSY if lock is already held
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* @raise ENOTRECOVERABLE if `mutex` is corrupted
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*/
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int pthread_mutex_trylock(pthread_mutex_t *mutex) {
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int c, d, t;
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if (LIKELY(__tls_enabled && //
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mutex->_type == PTHREAD_MUTEX_NORMAL && //
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mutex->_pshared == PTHREAD_PROCESS_PRIVATE && //
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weaken(nsync_mu_trylock))) {
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if (weaken(nsync_mu_trylock)((nsync_mu *)mutex)) {
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return 0;
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} else {
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return EBUSY;
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}
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}
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if (mutex->_type == PTHREAD_MUTEX_NORMAL) {
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c = 0;
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if (atomic_compare_exchange_strong_explicit(
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&mutex->_lock, &c, 1, memory_order_acquire, memory_order_relaxed)) {
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return 0;
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} else {
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return EBUSY;
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}
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}
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c = 0;
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t = gettid();
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d = 0x10100000 | t;
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if (!atomic_compare_exchange_strong_explicit(
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&mutex->_lock, &c, d, memory_order_acquire, memory_order_relaxed)) {
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if ((c & 0x000fffff) != t || mutex->_type == PTHREAD_MUTEX_ERRORCHECK) {
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return EBUSY;
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}
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if ((c & 0x0ff00000) == 0x0ff00000) {
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return EAGAIN;
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}
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atomic_fetch_add_explicit(&mutex->_lock, 0x00100000, memory_order_relaxed);
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}
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return 0;
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}
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