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Make more improvements to threads and mappings

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- NetBSD should now have faster synchronization
- POSIX barriers may now be shared across processes
- An edge case with memory map tracking has been fixed
- Grand Central Dispatch is no longer used on MacOS ARM64
- POSIX mutexes in normal mode now use futexes across processes
This commit is contained in:
Justine Tunney 2024-07-24 01:05:00 -07:00
parent 2187d6d2dd
commit e398f3887c
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GPG key ID: BE714B4575D6E328
20 changed files with 566 additions and 171 deletions
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92
libc/intrin/pthread_mutex_lock.c
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@ -27,41 +27,47 @@
#include "libc/runtime/internal.h"
#include "libc/thread/lock.h"
#include "libc/thread/thread.h"
#include "third_party/nsync/futex.internal.h"
#include "third_party/nsync/mu.h"
static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
int me;
static void pthread_mutex_lock_naive(pthread_mutex_t *mutex, uint64_t word) {
int backoff = 0;
uint64_t word, lock;
// get current state of lock
word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
#if PTHREAD_USE_NSYNC
// use fancy nsync mutex if possible
if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL && //
MUTEX_PSHARED(word) == PTHREAD_PROCESS_PRIVATE && //
_weaken(nsync_mu_lock)) {
_weaken(nsync_mu_lock)((nsync_mu *)mutex);
return 0;
uint64_t lock;
for (;;) {
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);
}
#endif
}
// implement barebones normal mutexes
if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {
for (;;) {
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 0;
backoff = pthread_delay_np(mutex, backoff);
}
// see "take 3" algorithm in "futexes are tricky" by ulrich drepper
// slightly improved to attempt acquiring multiple times b4 syscall
static void pthread_mutex_lock_drepper(atomic_int *futex, char pshare) {
int word;
for (int i = 0; i < 4; ++i) {
word = 0;
if (atomic_compare_exchange_strong_explicit(
futex, &word, 1, memory_order_acquire, memory_order_acquire))
return;
pthread_pause_np();
}
if (word == 1)
word = atomic_exchange_explicit(futex, 2, memory_order_acquire);
while (word > 0) {
_weaken(nsync_futex_wait_)(futex, 2, pshare, 0);
word = atomic_exchange_explicit(futex, 2, memory_order_acquire);
}
}
// implement recursive mutexes
me = gettid();
static errno_t pthread_mutex_lock_recursive(pthread_mutex_t *mutex,
uint64_t word) {
uint64_t lock;
int backoff = 0;
int me = gettid();
for (;;) {
if (MUTEX_OWNER(word) == me) {
if (MUTEX_TYPE(word) != PTHREAD_MUTEX_ERRORCHECK) {
@ -91,6 +97,36 @@ static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
}
}
static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
uint64_t word;
// get current state of lock
word = atomic_load_explicit(&mutex->_word, memory_order_relaxed);
#if PTHREAD_USE_NSYNC
// use superior mutexes if possible
if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL && //
MUTEX_PSHARED(word) == PTHREAD_PROCESS_PRIVATE && //
_weaken(nsync_mu_lock)) {
_weaken(nsync_mu_lock)((nsync_mu *)mutex);
return 0;
}
#endif
// handle normal mutexes
if (MUTEX_TYPE(word) == PTHREAD_MUTEX_NORMAL) {
if (_weaken(nsync_futex_wait_)) {
pthread_mutex_lock_drepper(&mutex->_futex, MUTEX_PSHARED(word));
} else {
pthread_mutex_lock_naive(mutex, word);
}
return 0;
}
// handle recursive and error checking mutexes
return pthread_mutex_lock_recursive(mutex, word);
}
/**
* Locks mutex.
*