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Example of a data race in Python
# Does Python have data races?
#
# As we've seen, Java can have data races, according to
# https://docs.oracle.com/javase/specs/jls/se8/html/jls-17.html
# It says an example of a data race is when:
# - there is a write in one thread,
# - a read of the same variable by another thread,
# - and the write and read are not ordered by synchronization.
#
# This program attempts to cause a data race in Python.
from threading import Thread
from time import sleep
counter = 0
def increase():
global counter
for i in range(0, 100000):
counter = counter + 1
threads = []
for i in range(0, 400):
threads.append(Thread(target=increase))
for thread in threads:
thread.start()
for thread in threads:
thread.join()
print(f'Final counter: {counter}')
# A few trials from my computer (Mac, 2.6 GHz 6-Core i7):
# Final counter: 31735072
# Final counter: 32829326
# Final counter: 31496003
#
# We conclude that yes, Python has data races.
@kprotty
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kprotty commented Sep 21, 2022

This seems like more of a race condition than a data race. You can get similar results in C/C++/Rust even when not hitting data races due to the operation as a whole not being atomic w.r.t concurrent thread execution:

atomic_store_explicit(&x, atomic_load_explicit(&x, memory_order_relaxed) + 1, memory_order_relaxed);

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