Python-多处理守护进程

Question

I'm creating a multiprocess, which creates a csv file. When I run the code with d.daemon = False it works fine, ie it creates a file in the same folder. But when compiled and run with d.daemon = True , it does not, ie does not creates a file. Why's so?

My Code

I've a seed list of URLs from which I need to scrape the data.

for url in config.SEED_LIST:
    # starting a new process for each category.
    d = multiprocessing.Process(target=workers.scrape, args=())
    d.daemon = True
    d.start()


def scrape():
    import time
    time.sleep(5)
    # The above part of code takes some time to scrape a webpage, applying
    # some logic, which takes some time to execute, hence I've added a time
    # sleep of 5 secs. But when run with daemon = True, the file is not
    # created. Else it works fine.

    data = [[1, 2, 3, 4], [2224, 34, 34, 34, 34]]
    with open('1.csv', "wb") as f:
        writer = csv.writer(f)
        writer.writerows(data)

Answer 1

According to multiprocess daemon documentation by setting d.daemon=True when your script ends its job will kill all subprocess. That occurs before they can start to write so no output will be produced.

Answer 2

d.daemon = True means that the subprocess is automatically terminated after the parent process ends to prevent orphan processes. join() is helpful by simply adding d.join() after d.start() , so that the parent process does not end before the child process; instead, the parent process will wait until the child process ends.