src/thread/pthread_mutex_trylock.c

   1 #include "pthread_impl.h"
   2
   3 int __pthread_mutex_trylock_owner(pthread_mutex_t *m)
   4 {
   5         int old, own;
   6         int type = m->_m_type;
   7         pthread_t self = __pthread_self();
   8         int tid = self->tid;
   9
  10         old = m->_m_lock;
  11         own = old & 0x3fffffff;
  12         if (own == tid && (type&3) == PTHREAD_MUTEX_RECURSIVE) {
  13                 if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
  14                 m->_m_count++;
  15                 return 0;
  16         }
  17         if (own == 0x3fffffff) return ENOTRECOVERABLE;
  18         if (own || (old && !(type & 4))) return EBUSY;
  19
  20         if (type & 128) {
  21                 if (!self->robust_list.off) {
  22                         self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
  23                         __syscall(SYS_set_robust_list, &self->robust_list, 3*sizeof(long));
  24                 }
  25                 if (m->_m_waiters) tid |= 0x80000000;
  26                 self->robust_list.pending = &m->_m_next;
  27         }
  28         tid |= old & 0x40000000;
  29
  30         if (a_cas(&m->_m_lock, old, tid) != old) {
  31                 self->robust_list.pending = 0;
  32                 return EBUSY;
  33         }
  34
  35         volatile void *next = self->robust_list.head;
  36         m->_m_next = next;
  37         m->_m_prev = &self->robust_list.head;
  38         if (next != &self->robust_list.head) *(volatile void *volatile *)
  39                 ((char *)next - sizeof(void *)) = &m->_m_next;
  40         self->robust_list.head = &m->_m_next;
  41         self->robust_list.pending = 0;
  42
  43         if (old) {
  44                 m->_m_count = 0;
  45                 return EOWNERDEAD;
  46         }
  47
  48         return 0;
  49 }
  50
  51 int __pthread_mutex_trylock(pthread_mutex_t *m)
  52 {
  53         if ((m->_m_type&15) == PTHREAD_MUTEX_NORMAL)
  54                 return a_cas(&m->_m_lock, 0, EBUSY) & EBUSY;
  55         return __pthread_mutex_trylock_owner(m);
  56 }
  57
  58 weak_alias(__pthread_mutex_trylock, pthread_mutex_trylock);