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Revert "Make spin locks go faster"

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This reverts commit c8e25d811c.
This commit is contained in:
Justine Tunney 2024-07-25 22:24:32 -07:00
parent 0679cfeb41
commit 02e1cbcd00
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GPG key ID: BE714B4575D6E328
16 changed files with 122 additions and 149 deletions
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26
libc/intrin/pthread_mutex_lock.c
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@ -31,16 +31,17 @@
#include "third_party/nsync/futex.internal.h"
#include "third_party/nsync/mu.h"
static void pthread_mutex_lock_spin(atomic_int *word) {
static void pthread_mutex_lock_naive(pthread_mutex_t *mutex, uint64_t word) {
int backoff = 0;
uint64_t lock;
for (;;) {
if (!atomic_exchange_explicit(word, 1, memory_order_acquire))
break;
for (;;) {
if (!atomic_load_explicit(word, memory_order_relaxed))
break;
backoff = pthread_delay_np(word, backoff);
}
word = MUTEX_UNLOCK(word);
lock = MUTEX_LOCK(word);
if (atomic_compare_exchange_weak_explicit(&mutex->_word, &word, lock,
memory_order_acquire,
memory_order_relaxed))
return;
backoff = pthread_delay_np(mutex, backoff);
}
}
@ -95,12 +96,7 @@ static errno_t pthread_mutex_lock_recursive(pthread_mutex_t *mutex,
mutex->_pid = __pid;
return 0;
}
for (;;) {
word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
if (!MUTEX_LOCKED(word))
break;
backoff = pthread_delay_np(mutex, backoff);
}
backoff = pthread_delay_np(mutex, backoff);
}
}
@ -125,7 +121,7 @@ static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
if (_weaken(nsync_futex_wait_)) {
pthread_mutex_lock_drepper(&mutex->_futex, MUTEX_PSHARED(word));
} else {
pthread_mutex_lock_spin(&mutex->_futex);
pthread_mutex_lock_naive(mutex, word);
}
return 0;
}