mirror of
https://github.com/jart/cosmopolitan.git
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90 lines
3.9 KiB
C
90 lines
3.9 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/calls/calls.h"
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#include "libc/dce.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/strace.h"
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#include "libc/intrin/weaken.h"
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#include "libc/runtime/internal.h"
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#include "libc/thread/lock.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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* Releases mutex.
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*
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* This function does nothing in vfork() children.
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*
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* @return 0 on success or error number on failure
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* @raises EPERM if in error check mode and not owned by caller
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* @vforksafe
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*/
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errno_t pthread_mutex_unlock(pthread_mutex_t *mutex) {
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int me;
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uint64_t word, lock;
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LOCKTRACE("pthread_mutex_unlock(%t)", mutex);
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// get current state of lock
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word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
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#if PTHREAD_USE_NSYNC
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// use fancy nsync mutex if possible
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if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL && //
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MUTEX_PSHARED(word) == PTHREAD_PROCESS_PRIVATE && //
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_weaken(nsync_mu_unlock)) {
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_weaken(nsync_mu_unlock)((nsync_mu *)mutex);
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return 0;
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}
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#endif
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// implement barebones normal mutexes
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if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {
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lock = MUTEX_UNLOCK(word);
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atomic_store_explicit(&mutex->_word, lock, memory_order_release);
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return 0;
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}
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// implement recursive mutex unlocking
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me = gettid();
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for (;;) {
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// we allow unlocking an initialized lock that wasn't locked, but we
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// don't allow unlocking a lock held by another thread, or unlocking
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// recursive locks from a forked child, since it should be re-init'd
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if (MUTEX_OWNER(word) && (MUTEX_OWNER(word) != me || mutex->_pid != __pid))
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return EPERM;
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// check if this is a nested lock with signal safety
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if (MUTEX_DEPTH(word)) {
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if (atomic_compare_exchange_weak_explicit(
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&mutex->_word, &word, MUTEX_DEC_DEPTH(word), memory_order_relaxed,
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memory_order_relaxed))
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return 0;
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continue;
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}
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// actually unlock the mutex
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if (atomic_compare_exchange_weak_explicit(
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&mutex->_word, &word, MUTEX_UNLOCK(word), memory_order_release,
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memory_order_relaxed))
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return 0;
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}
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}
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