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90460ceb3c
While we have always licked glibc and musl libc on gnu/systemd sadly the Apple Libc implementation of pthread_mutex_t is better than ours. It may be due to how the XNU kernel and M2 microprocessor are in league when it comes to scheduling processes and the NSYNC behavior is being penalized. We can solve this by leaning more heavily on ulock using Drepper's algo. It's kind of ironic that Linux's official mutexes work terribly on Linux but almost as good as Apple Libc if used on MacOS.
63 lines
3.4 KiB
C
63 lines
3.4 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/intrin/strace.h"
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#include "libc/thread/thread.h"
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/**
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* Acquires spin lock, e.g.
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*
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* pthread_spinlock_t lock;
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* pthread_spin_init(&lock, PTHREAD_PROCESS_PRIVATE);
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* pthread_spin_lock(&lock);
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* // do work...
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* pthread_spin_unlock(&lock);
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* pthread_spin_destroy(&lock);
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*
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* This function has undefined behavior when `spin` wasn't intialized or
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* was destroyed, and if the lock is already held by the calling thread.
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*
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* You can debug locks the acquisition of locks by building your program
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* with `cosmocc -mdbg` and passing the `--strace` flag to your program.
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* This will cause a line to be logged each time a mutex or spin lock is
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* locked or unlocked. When locking, this is printed after the lock gets
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* acquired. The entry to the lock operation will be logged too but only
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* if the lock couldn't be immediately acquired. Lock logging works best
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* when `mutex` refers to a static variable, in which case its name will
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* be printed in the log.
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*
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* @return 0 on success, or errno on error
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* @see pthread_spin_trylock
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* @see pthread_spin_unlock
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* @see pthread_spin_init
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*/
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errno_t pthread_spin_lock(pthread_spinlock_t *spin) {
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if (atomic_exchange_explicit(&spin->_lock, 1, memory_order_acquire)) {
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LOCKTRACE("acquiring pthread_spin_lock(%t)...", spin);
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for (;;) {
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for (;;)
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if (!atomic_load_explicit(&spin->_lock, memory_order_relaxed))
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break;
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if (!atomic_exchange_explicit(&spin->_lock, 1, memory_order_acquire))
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break;
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}
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}
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LOCKTRACE("pthread_spin_lock(%t)", spin);
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return 0;
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}
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