[Tutor] Multiprocessing question

[Albert-Jan Roskam]

   By the way, I should have added that I'm using Python 3.8. The test script
   was written on Linux Debian Jesse. Target system is RHEL 8.
   So no Windows involved!
   On Oct 29, 2023 15:27, Albert-Jan Roskam <sjeik_appie at hotmail.com> wrote:

        Hi,
        I'm trying to create multiprocessing task that runs multiple SQL
     queries
        in parallel (COPY TO csv), then adds those csv files to a zip. In the
     code
        below, tge csv files don't end up in the zip. Why not?
        I'm using a buffer instead of a file for the zip because in my actual
        scenario, a Flask endpoint returns the .zip
        Thanks in advance!
        Albert-Jan
        import io
        import logging
        import multiprocessing as mp
        #from multiprocessing.shared_memory import SharedMemory
        from random import randint
        from time import sleep
        from zipfile import ZipFile, ZIP_DEFLATED
        mp.log_to_stderr(logging.DEBUG)
        def task(lock, archive):
            # Do some work in parellel (SQL), followed
            # by adding the query result to a zip
            name = mp.current_process().name
            print(f"==begin {name}")
            sleep(randint(1, 5))
            csv_buff = io.BytesIO(b"name = " + name.encode("utf-8"))
            with lock:
                print(f"* begin zipping {name}")
                sleep(randint(1, 5))
                data = csv_buff.getvalue()
                print("csv data", data)
                archive.writestr(name, data)
                print(f"* end zipping {name}")
            print(f"==end {name}")
        def main():
            #shm = SharedMemory(create=True, size=2048) # read-only! :-(
            #zip_buff = shm.buf
            zip_buff = io.BytesIO()
            archive = ZipFile(zip_buff, "w", ZIP_DEFLATED, False, 2)
            lock = mp.Lock()
            procs = [mp.Process(target=task, args=(lock, archive)) for _ in
        range(3)]
            for proc in procs:
                proc.start()
            for proc in procs:
                proc.join()
            with archive:
                archive.writestr("main", b"from main")
            zip_buff.seek(0)
            data = zip_buff.getvalue()
            assert len(data), "No data!"
            print("data:", data)

            with open("archive.zip", mode="wb") as archive:
                archive.write(data)
        if __name__ == "__main__":
            main()
     _______________________________________________
     Tutor maillist  -  Tutor at python.org
     To unsubscribe or change subscription options:
     https://mail.python.org/mailman/listinfo/tutor