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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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26
libc/thread/pthread_rwlock_tryrdlock.c
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@ -17,6 +17,7 @@
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/errno.h"
#include "libc/intrin/atomic.h"
#include "libc/thread/thread.h"
#include "third_party/nsync/mu.h"
@ -29,9 +30,26 @@
* @raise EINVAL if `rwlock` doesn't refer to an initialized r/w lock
*/
errno_t pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock) {
if (nsync_mu_rtrylock((nsync_mu *)rwlock)) {
return 0;
} else {
return EBUSY;
#if PTHREAD_USE_NSYNC
// use nsync if possible
if (!rwlock->_pshared) {
if (nsync_mu_rtrylock((nsync_mu *)rwlock->_nsync)) {
return 0;
} else {
return EBUSY;
}
}
#endif
// naive implementation
uint32_t word = 0;
for (;;) {
if (word & 1)
return EBUSY;
if (atomic_compare_exchange_weak_explicit(&rwlock->_word, &word, word + 2,
memory_order_acquire,
memory_order_relaxed))
return 0;
}
}