Python and threading don't mix

tarthread.py

#!/usr/bin/python3
# Write to a tarball from multiple threads to demonstrate corruption.

import tarfile, threading, io

N_THREADS = 8

def append_tar(tarf, val):
    tf = tarfile.TarInfo(name="{}".format(val))
    # Generate an entry with the unique byte
    # repeated so it's easy to see intermixed content.
    tf.size = 4096
    buf = bytearray([val for x in range(tf.size)])
    tarf.addfile(tf, io.BytesIO(buf))

tarf = tarfile.open("out.tar", mode='w')
threads = []
for x in range(N_THREADS):
    t = threading.Thread(target=lambda: append_tar(tarf, x))
    t.start()
    threads.append(t)
for t in threads:
    t.join()