int sem_wait(sem_t * sem)
{
long oldstatus, newstatus;
volatile pthread_t self = thread_self();
pthread_t * th;
while (1) {
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) && (oldstatus != 1))
newstatus = oldstatus - 2;
else {
newstatus = (long) self;
self->p_nextwaiting = (pthread_t) oldstatus;
}
}
while (! compare_and_swap(sem, oldstatus, newstatus));
if (newstatus & 1)
/* We got the semaphore. */
return 0;
/* Wait for sem_post or cancellation */
suspend_with_cancellation(self);
/* This is a cancellation point */
if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
/* Remove ourselves from the waiting list if we're still on it */
/* First check if we're at the head of the list. */
do {
oldstatus = sem->sem_status;
if (oldstatus != (long) self) break;
newstatus = (long) self->p_nextwaiting;
}
while (! compare_and_swap(sem, oldstatus, newstatus));
/* Now, check if we're somewhere in the list.
There's a race condition with sem_post here, but it does not matter:
the net result is that at the time pthread_exit is called,
self is no longer reachable from sem->sem_status. */
if (oldstatus != (long) self && (oldstatus & 1) == 0) {
th = &(((pthread_t) oldstatus)->p_nextwaiting);
while (*th != (pthread_t) 1 && *th != NULL) {
if (*th == self) {
*th = self->p_nextwaiting;
break;
}
th = &((*th)->p_nextwaiting);
}
}
pthread_exit(PTHREAD_CANCELED);
}
}
}
int pthread_join(pthread_t thread_id, void ** thread_return)
{
volatile pthread_descr self = thread_self();
struct pthread_request request;
pthread_handle handle = thread_handle(thread_id);
pthread_descr th;
acquire(&handle->h_spinlock);
if (invalid_handle(handle, thread_id)) {
release(&handle->h_spinlock);
return ESRCH;
}
th = handle->h_descr;
if (th == self) {
release(&handle->h_spinlock);
return EDEADLK;
}
/* If detached or already joined, error */
if (th->p_detached || th->p_joining != NULL) {
release(&handle->h_spinlock);
return EINVAL;
}
/* If not terminated yet, suspend ourselves. */
if (! th->p_terminated) {
th->p_joining = self;
release(&handle->h_spinlock);
suspend_with_cancellation(self);
/* This is a cancellation point */
if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
th->p_joining = NULL;
pthread_exit(PTHREAD_CANCELED);
}
acquire(&handle->h_spinlock);
}
/* Get return value */
if (thread_return != NULL) *thread_return = th->p_retval;
release(&handle->h_spinlock);
/* Send notification to thread manager */
if (__pthread_manager_request >= 0) {
request.req_thread = self;
request.req_kind = REQ_FREE;
request.req_args.free.thread = th;
write(__pthread_manager_request, (char *) &request, sizeof(request));
}
return 0;
}
