import threading, queue

event_pool = [torch.cuda.Event() for _ in range(POSTPROC_WORKERS)]
event_queue = queue.Queue()

def event_monitor(event_pool, event_queue, output_queue):
    while True:
        item = event_queue.get()
        if item is None: break
        batch_id, buf_idx = item
        event_pool[buf_idx].synchronize()
        output_queue.put((batch_id, buf_idx))
        event_queue.task_done()

monitor = threading.Thread(target=event_monitor,
                           args=(event_pool, event_queue, output_queue))
monitor.start()