source: azure_iot_hub/trunk/musl-1.1.18/src/thread/pthread_mutex_trylock.c@ 389

#include "pthread_impl.h"

int __pthread_mutex_trylock_owner(pthread_mutex_t *m)
{
        int old, own;
        int type = m->_m_type & 15;
        pthread_t self = __pthread_self();
        int tid = self->tid;

        old = m->_m_lock;
        own = old & 0x7fffffff;
        if (own == tid && (type&3) == PTHREAD_MUTEX_RECURSIVE) {
                if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
                m->_m_count++;
                return 0;
        }
        if (own == 0x7fffffff) return ENOTRECOVERABLE;

        if (m->_m_type & 128) {
                if (!self->robust_list.off) {
                        self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
                        __syscall(SYS_set_robust_list, &self->robust_list, 3*sizeof(long));
                }
                if (m->_m_waiters) tid |= 0x80000000;
                self->robust_list.pending = &m->_m_next;
        }

        if ((own && (!(own & 0x40000000) || !(type & 4)))
            || a_cas(&m->_m_lock, old, tid) != old) {
                self->robust_list.pending = 0;
                return EBUSY;
        }

        volatile void *next = self->robust_list.head;
        m->_m_next = next;
        m->_m_prev = &self->robust_list.head;
        if (next != &self->robust_list.head) *(volatile void *volatile *)
                ((char *)next - sizeof(void *)) = &m->_m_next;
        self->robust_list.head = &m->_m_next;
        self->robust_list.pending = 0;

        if (own) {
                m->_m_count = 0;
                m->_m_type |= 8;
                return EOWNERDEAD;
        }

        return 0;
}

int __pthread_mutex_trylock(pthread_mutex_t *m)
{
        if ((m->_m_type&15) == PTHREAD_MUTEX_NORMAL)
                return a_cas(&m->_m_lock, 0, EBUSY) & EBUSY;
        return __pthread_mutex_trylock_owner(m);
}

#ifndef __c2__
weak_alias(__pthread_mutex_trylock, pthread_mutex_trylock);
#else
int pthread_mutex_trylock(pthread_mutex_t *m)
{
        return __pthread_mutex_trylock(m);
}
#endif