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) {
  13                 if ((type&8) && m->_m_count<0) {
  14                         old &= 0x40000000;
  15                         m->_m_count = 0;
  16                         goto success;
  17                 }
  18                 if ((type&3) == PTHREAD_MUTEX_RECURSIVE) {
  19                         if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
  20                         m->_m_count++;
  21                         return 0;
  22                 }
  23         }
  24         if (own == 0x3fffffff) return ENOTRECOVERABLE;
  25         if (own || (old && !(type & 4))) return EBUSY;
  26
  27         if (type & 128) {
  28                 if (!self->robust_list.off) {
  29                         self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
  30                         __syscall(SYS_set_robust_list, &self->robust_list, 3*sizeof(long));
  31                 }
  32                 if (m->_m_waiters) tid |= 0x80000000;
  33                 self->robust_list.pending = &m->_m_next;
  34         }
  35         tid |= old & 0x40000000;
  36
  37         if (a_cas(&m->_m_lock, old, tid) != old) {
  38                 self->robust_list.pending = 0;
  39                 if ((type&12)==12 & m->_m_waiters) return ENOTRECOVERABLE;
  40                 return EBUSY;
  41         }
  42
  43 success:
  44         if ((type&8) && m->_m_waiters) {
  45                 int priv = (type & 128) ^ 128;
  46                 __syscall(SYS_futex, &m->_m_lock, FUTEX_UNLOCK_PI|priv);
  47                 self->robust_list.pending = 0;
  48                 return (type&4) ? ENOTRECOVERABLE : EBUSY;
  49         }
  50
  51         volatile void *next = self->robust_list.head;
  52         m->_m_next = next;
  53         m->_m_prev = &self->robust_list.head;
  54         if (next != &self->robust_list.head) *(volatile void *volatile *)
  55                 ((char *)next - sizeof(void *)) = &m->_m_next;
  56         self->robust_list.head = &m->_m_next;
  57         self->robust_list.pending = 0;
  58
  59         if (old) {
  60                 m->_m_count = 0;
  61                 return EOWNERDEAD;
  62         }
  63
  64         return 0;
  65 }
  66
  67 int __pthread_mutex_trylock(pthread_mutex_t *m)
  68 {
  69         if ((m->_m_type&15) == PTHREAD_MUTEX_NORMAL)
  70                 return a_cas(&m->_m_lock, 0, EBUSY) & EBUSY;
  71         return __pthread_mutex_trylock_owner(m);
  72 }
  73
  74 weak_alias(__pthread_mutex_trylock, pthread_mutex_trylock);