overhaul rwlocks to address several issues

[musl] / src / thread / pthread_rwlock_trywrlock.c

#include "pthread_impl.h"

int pthread_rwlock_trywrlock(pthread_rwlock_t *rw)
{
        if (a_cas(&rw->_rw_lock, 0, 0x7fffffff)) return EBUSY;
        return 0;
}