mirrors/cosmopolitan
1
0
Fork 0
mirror of https://github.com/jart/cosmopolitan.git synced 2025-04-16 11:54:58 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 1

Avoid pthread_rwlock_wrlock() starvation

Browse source
This commit is contained in:
Justine Tunney 2024-12-24 10:30:11 -08:00
parent 55b7aa1632
commit ec2db4e40e
No known key found for this signature in database
GPG key ID: BE714B4575D6E328
3 changed files with 6 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
libc/thread/pthread_rwlock_rdlock.c
View file

@ -42,6 +42,9 @@ errno_t pthread_rwlock_rdlock(pthread_rwlock_t *lk) {
for (;;) for (;;)
if (~(w = atomic_load_explicit(&lk->_word, memory_order_relaxed)) & 1) if (~(w = atomic_load_explicit(&lk->_word, memory_order_relaxed)) & 1)
break; break;
// xxx: avoid writer starvation in pthread_rwlock_rdlock_test
while (atomic_load(&lk->_waiters))
pthread_yield_np();
if (atomic_compare_exchange_weak_explicit( if (atomic_compare_exchange_weak_explicit(
&lk->_word, &w, w + 2, memory_order_acquire, memory_order_relaxed)) &lk->_word, &w, w + 2, memory_order_acquire, memory_order_relaxed))
return 0; return 0;

2
libc/thread/pthread_rwlock_wrlock.c
View file

@ -42,8 +42,10 @@ errno_t pthread_rwlock_wrlock(pthread_rwlock_t *rwlock) {
if (atomic_compare_exchange_weak_explicit( if (atomic_compare_exchange_weak_explicit(
&rwlock->_word, &w, 1, memory_order_acquire, memory_order_relaxed)) &rwlock->_word, &w, 1, memory_order_acquire, memory_order_relaxed))
return 0; return 0;
atomic_fetch_add(&rwlock->_waiters, 1);
for (;;) for (;;)
if (!(w = atomic_load_explicit(&rwlock->_word, memory_order_relaxed))) if (!(w = atomic_load_explicit(&rwlock->_word, memory_order_relaxed)))
break; break;
atomic_fetch_sub(&rwlock->_waiters, 1);
} }
} }

1
libc/thread/thread.h
View file

@ -111,6 +111,7 @@ typedef struct pthread_rwlock_s {
char _pshared; char _pshared;
char _iswrite; char _iswrite;
_PTHREAD_ATOMIC(uint32_t) _word; _PTHREAD_ATOMIC(uint32_t) _word;
_PTHREAD_ATOMIC(uint32_t) _waiters;
}; };
}; };
} pthread_rwlock_t; } pthread_rwlock_t;