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Support process shared pthread_rwlock

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Cosmo now has a non-nsync implementation of POSIX read-write locks. It's
possible to call pthread_rwlockattr_setpshared in PTHREAD_PROCESS_SHARED
mode. Furthermore, if cosmo is built with PTHREAD_USE_NSYNC set to zero,
then Cosmo shouldn't use nsync at all. That's helpful if you want to not
link any Apache 2.0 licensed code.
This commit is contained in:
Justine Tunney 2024-12-13 02:50:19 -08:00
parent c22b413ac4
commit 2d43d400c6
No known key found for this signature in database
GPG key ID: BE714B4575D6E328
11 changed files with 179 additions and 35 deletions
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25
libc/thread/pthread_rwlock_rdlock.c
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@ -16,6 +16,7 @@
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/intrin/atomic.h"
#include "libc/thread/thread.h"
#include "third_party/nsync/mu.h"
@ -24,7 +25,25 @@
*
* @return 0 on success, or errno on error
*/
errno_t pthread_rwlock_rdlock(pthread_rwlock_t *rwlock) {
nsync_mu_rlock((nsync_mu *)rwlock);
return 0;
errno_t pthread_rwlock_rdlock(pthread_rwlock_t *lk) {
#if PTHREAD_USE_NSYNC
// use nsync if possible
if (!lk->_pshared) {
nsync_mu_rlock((nsync_mu *)lk->_nsync);
return 0;
}
#endif
// naive implementation
uint32_t w = 0;
for (;;) {
if (w & 1)
for (;;)
if (~(w = atomic_load_explicit(&lk->_word, memory_order_relaxed)) & 1)
break;
if (atomic_compare_exchange_weak_explicit(
&lk->_word, &w, w + 2, memory_order_acquire, memory_order_relaxed))
return 0;
}
}