/*
 * Document-method: pop
 * call_seq: pop(non_block=false)
 *
 * Retrieves data from the queue.  If the queue is empty, the calling thread is
 * suspended until data is pushed onto the queue.  If +non_block+ is true, the
 * thread isn't suspended, and an exception is raised.
 *
 */

static VALUE
rb_queue_pop(int argc, VALUE *argv, VALUE self)
{
    Queue *queue;
    int should_block;
    VALUE result;
    Data_Get_Struct(self, Queue, queue);

    if (argc == 0) {
        should_block = 1;
    } else if (argc == 1) {
        should_block = !RTEST(argv[0]);
    } else {
        rb_raise(rb_eArgError, "wrong number of arguments (%d for 1)", argc);
    }

    lock_mutex(&queue->mutex);
    if (!queue->values.entries && !should_block) {
        unlock_mutex(&queue->mutex);
        rb_raise(private_eThreadError, "queue empty");
    }

    while (!queue->values.entries) {
        wait_condvar(&queue->value_available, &queue->mutex);
    }

    result = shift_list(&queue->values);
    if (queue->capacity && queue->values.size < queue->capacity) {
        signal_condvar(&queue->space_available);
    }
    unlock_mutex(&queue->mutex);

    return result;
}