void lock()
{
while (1)
{
if (!xchg_32(&_lock, EBUSY)) return;
while (_lock) cpu_relax();
}
}
int32_t mutex_lock(mutex_t *m)
{
DEBUG(fprintf(stderr, "[%d] mutex_lock start\n", pthread_self()));
int32_t i, c;
/* Spin and try to take lock */
#ifdef SPIN
for (i = 0; i < SPIN_TIMES; i++)
{
#endif
c = atomic_cmpxchg_32(m, UNLOCK, LOCKED);
if (!c) {
DEBUG(fprintf(stderr, "[%d] mutex_lock end\n", pthread_self()));
return 0;
}
cpu_relax();
#ifdef SPIN
}
#endif
/* The lock is now contended */
if (c == LOCKED) c = xchg_32(m, LOCKED_WITH_WAITERS);
while (c)
{
/* Wait in the kernel */
int32_t ret = syscall(SYS_futex, m, FUTEX_WAIT_PRIVATE, LOCKED_WITH_WAITERS, NULL, NULL, 0);
DEBUG(fprintf(stderr, "[%d] syscall(SYS_futex, 0x%p, FUTEX_WAIT_PRIVATE, %d, %p, %p, %d)=%d\n",
pthread_self(), m, LOCKED_WITH_WAITERS, NULL, NULL, 0, ret));
c = xchg_32(m, LOCKED_WITH_WAITERS);
}
DEBUG(fprintf(stderr, "[%d] mutex_lock end\n", pthread_self()));
return 0;
}
int32_t mutex_unlock(mutex_t *m)
{
DEBUG(fprintf(stderr, "[%d] mutex_unlock start\n", pthread_self()));
int32_t i;
/* Unlock, and if not contended then exit. */
if (*m == LOCKED_WITH_WAITERS)
{
*m = UNLOCK;
}
else if (xchg_32(m, UNLOCK) == LOCKED) {
DEBUG(fprintf(stderr, "[%d] mutex_unlock end\n", pthread_self()));
return 0;
}
/* Spin and hope someone takes the lock */
#ifdef SPIN
for (i = 0; i < SPIN_TIMES; i++)
{
#endif
if (*m)
{
/* Need to set to state 2 because there may be waiters */
if (atomic_cmpxchg_32(m, LOCKED, LOCKED_WITH_WAITERS)) {
DEBUG(fprintf(stderr, "[%d] mutex_unlock end\n", pthread_self()));
return 0;
}
}
cpu_relax();
#ifdef SPIN
}
#endif
/* We need to wake someone up */
int32_t ret = syscall(SYS_futex, m, FUTEX_WAKE_PRIVATE, 1, NULL, NULL, 0);
DEBUG(fprintf(stderr, "[%d] syscall(SYS_futex, 0x%p, FUTEX_WAKE_PRIVATE, %d, %p, %p, %d)=%d\n",
pthread_self(), m, 1, NULL, NULL, 0, ret));
DEBUG(fprintf(stderr, "[%d] mutex_unlock end\n", pthread_self()));
return 0;
}