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Introduce cosmo_futex_wait and cosmo_futex_wake

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Cosmopolitan Futexes are now exposed as a public API.
This commit is contained in:
Justine Tunney 2024-11-22 11:08:29 -08:00
parent 729f7045e3
commit 9ddbfd921e
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GPG key ID: BE714B4575D6E328
66 changed files with 886 additions and 917 deletions
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26
libc/intrin/pthread_mutex_lock.c
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@ -19,6 +19,7 @@
#include "libc/calls/blockcancel.internal.h"
#include "libc/calls/calls.h"
#include "libc/calls/state.internal.h"
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/errno.h"
#include "libc/intrin/atomic.h"
@ -28,25 +29,8 @@
#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 void pthread_mutex_lock_spin(atomic_int *word) {
int backoff = 0;
if (atomic_exchange_explicit(word, 1, memory_order_acquire)) {
LOCKTRACE("acquiring pthread_mutex_lock_spin(%t)...", word);
for (;;) {
for (;;) {
if (!atomic_load_explicit(word, memory_order_relaxed))
break;
backoff = pthread_delay_np(word, backoff);
}
if (!atomic_exchange_explicit(word, 1, memory_order_acquire))
break;
}
}
}
// 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) {
@ -59,7 +43,7 @@ static void pthread_mutex_lock_drepper(atomic_int *futex, char pshare) {
word = atomic_exchange_explicit(futex, 2, memory_order_acquire);
BLOCK_CANCELATION;
while (word > 0) {
_weaken(nsync_futex_wait_)(futex, 2, pshare, 0, 0);
cosmo_futex_wait(futex, 2, pshare, 0, 0);
word = atomic_exchange_explicit(futex, 2, memory_order_acquire);
}
ALLOW_CANCELATION;
@ -164,11 +148,7 @@ static errno_t pthread_mutex_lock_impl(pthread_mutex_t *mutex) {
// 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_spin(&mutex->_futex);
}
pthread_mutex_lock_drepper(&mutex->_futex, MUTEX_PSHARED(word));
return 0;
}