Example of a data race in Python
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# 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. |
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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: