redesign robust mutex states to eliminate data races on type field

[musl] / src / thread / pthread_mutex_timedlock.c

diff --git a/src/thread/pthread_mutex_timedlock.c b/src/thread/pthread_mutex_timedlock.c
index 7b1afc0..b95af25 100644 (file)
--- a/src/thread/pthread_mutex_timedlock.c
+++ b/src/thread/pthread_mutex_timedlock.c
@@ -1,24 +1,37 @@
 #include "pthread_impl.h"
 
-int pthread_mutex_timedlock(pthread_mutex_t *restrict m, const struct timespec *restrict at)
+int __pthread_mutex_timedlock(pthread_mutex_t *restrict m, const struct timespec *restrict at)
 {
-       int r, t;
-
-       if (m->_m_type == PTHREAD_MUTEX_NORMAL && !a_cas(&m->_m_lock, 0, EBUSY))
+       if ((m->_m_type&15) == PTHREAD_MUTEX_NORMAL
+           && !a_cas(&m->_m_lock, 0, EBUSY))
                return 0;
 
-       while ((r=pthread_mutex_trylock(m)) == EBUSY) {
-               if (!(r=m->_m_lock) || (r&0x40000000)) continue;
-               if ((m->_m_type&3) == PTHREAD_MUTEX_ERRORCHECK
-                && (r&0x1fffffff) == __pthread_self()->tid)
+       int type = m->_m_type;
+       int r, t, priv = (type & 128) ^ 128;
+
+       r = pthread_mutex_trylock(m);
+       if (r != EBUSY) return r;
+       
+       int spins = 100;
+       while (spins-- && m->_m_lock && !m->_m_waiters) a_spin();
+
+       while ((r=__pthread_mutex_trylock(m)) == EBUSY) {
+               r = m->_m_lock;
+               int own = r & 0x3fffffff;
+               if (!own && (!r || (type&4)))
+                       continue;
+               if ((type&3) == PTHREAD_MUTEX_ERRORCHECK
+                   && own == __pthread_self()->tid)
                        return EDEADLK;
 
                a_inc(&m->_m_waiters);
                t = r | 0x80000000;
                a_cas(&m->_m_lock, r, t);
-               r = __timedwait(&m->_m_lock, t, CLOCK_REALTIME, at, 0, 0, 0);
+               r = __timedwait(&m->_m_lock, t, CLOCK_REALTIME, at, priv);
                a_dec(&m->_m_waiters);
                if (r && r != EINTR) break;
        }
        return r;
 }
+
+weak_alias(__pthread_mutex_timedlock, pthread_mutex_timedlock);