multiprocessing worker code not executing

Question

I have code like this:

def worker(data_row):
    print("In worker", data_row)

if __name__ == '__main__':
    db_conn = init_db_conn()
    rows = db_conn.execute(query).fetchall()
    
    db_conn.close()

    pool = Pool(4)
    jobs = []
    for row in rows:
        print("In main", row)
        job = pool.apply_async(worker, (row,))
        jobs.append(job)

    for job in jobs:
        job.get()

    pool.join()
    pool.close()

When I execute this, only In main are printed, and zero In worker, so no worker code is executed. How to resolve this?

Answer 1

from the docs you have to call close before join.

class multiprocessing.pool.Pool

close()
    Prevents any more tasks from being submitted to the pool. 
    Once all the tasks have been completed the worker processes will exit.

terminate()
    Stops the worker processes immediately without completing 
    outstanding work. When the pool object is garbage collected 
    terminate() will be called immediately.

join()
    Wait for the worker processes to exit. 
    One must call close() or terminate() before using join().