Python multiprocessing - How to release memory when a process is done?

Question

I encountered a weird problem while using python multiprocessing library.

My code is sketched below: I spawn a process for each "symbol, date" tuple. I combine the results afterwards.

I expect that when a process has done computing for a "symbol, date" tuple, it should release its memory? apparently that's not the case. I see dozens of processes (though I set the process pool to have size 7) that are suspended¹ in the machine. They consume no CPU, and they don't release the memory.

How do I let a process release its memory, after it has done its computation?

Thanks!

¹ by "suspended" I mean their status in ps command is shown as "S+"

def do_one_symbol( symbol, all_date_strings ):     pool = Pool(processes=7)     results = [];     for date in all_date_strings:         res = pool.apply_async(work, [symbol, date])         results.append(res);      gg = mm = ss = 0;     for res in results:         g, m, s = res.get()         gg += g;          mm += m;          ss += s; 

Answer 1

Did you try to close pool by using pool.close and then wait for process to finish by pool.join, because if parent process keeps on running and does not wait for child processes they will become zombies