fusl/src/thread/pthread_mutex_trylock.c

#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 == 0x40000000)
    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);
}

weak_alias(__pthread_mutex_trylock, pthread_mutex_trylock);