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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.
123 lines
5 KiB
C
123 lines
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 et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 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/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/futex.internal.h"
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#include "third_party/nsync/mu.h"
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static errno_t pthread_mutex_trylock_spin(atomic_int *word) {
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if (!atomic_exchange_explicit(word, 1, memory_order_acquire))
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return 0;
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return EBUSY;
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}
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static errno_t pthread_mutex_trylock_drepper(atomic_int *futex) {
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int word = 0;
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if (atomic_compare_exchange_strong_explicit(
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futex, &word, 1, memory_order_acquire, memory_order_acquire))
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return 0;
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return EBUSY;
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}
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static errno_t pthread_mutex_trylock_recursive(pthread_mutex_t *mutex,
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uint64_t word) {
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uint64_t lock;
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int me = gettid();
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for (;;) {
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if (MUTEX_OWNER(word) == me) {
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if (MUTEX_TYPE(word) != PTHREAD_MUTEX_ERRORCHECK) {
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if (MUTEX_DEPTH(word) < MUTEX_DEPTH_MAX) {
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if (atomic_compare_exchange_weak_explicit(
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&mutex->_word, &word, MUTEX_INC_DEPTH(word),
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memory_order_relaxed, memory_order_relaxed))
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return 0;
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continue;
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} else {
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return EAGAIN;
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}
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} else {
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return EDEADLK;
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}
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}
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word = MUTEX_UNLOCK(word);
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lock = MUTEX_LOCK(word);
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lock = MUTEX_SET_OWNER(lock, me);
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if (atomic_compare_exchange_weak_explicit(&mutex->_word, &word, lock,
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memory_order_acquire,
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memory_order_relaxed)) {
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mutex->_pid = __pid;
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return 0;
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}
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return EBUSY;
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}
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}
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/**
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* Attempts acquiring lock.
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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 if lock was acquired, otherwise an errno
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* @raise EAGAIN if maximum number of recursive locks is held
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* @raise EBUSY if lock is currently held in read or write mode
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* @raise EINVAL if `mutex` doesn't refer to an initialized lock
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* @raise EDEADLK if `mutex` is `PTHREAD_MUTEX_ERRORCHECK` and the
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* current thread already holds this mutex
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*/
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errno_t pthread_mutex_trylock(pthread_mutex_t *mutex) {
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// get current state of lock
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uint64_t word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
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#if PTHREAD_USE_NSYNC
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// use superior mutexes 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_trylock)) {
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// on apple silicon we should just put our faith in ulock
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// otherwise *nsync gets struck down by the eye of sauron
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if (!IsXnuSilicon()) {
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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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}
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#endif
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// handle normal mutexes
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if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {
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if (_weaken(nsync_futex_wait_)) {
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return pthread_mutex_trylock_drepper(&mutex->_futex);
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} else {
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return pthread_mutex_trylock_spin(&mutex->_futex);
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}
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}
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// handle recursive and error checking mutexes
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return pthread_mutex_trylock_recursive(mutex, word);
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}
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