Locks in Python

Guarding shared state so threads don't corrupt it.

import threading

total = 0
lock = threading.Lock()


def add_many(times):
    global total
    for _ in range(times):
        with lock:
            total += 1


threads = [threading.Thread(target=add_many, args=(10_000,))
           for _ in range(4)]
for t in threads:
    t.start()
for t in threads:
    t.join()

How it works

1. Four threads all increment the same total.
2. with lock: makes each increment atomic.
3. join waits for every thread to finish.

Keywords and builtins used here

• add_many
• def
• for
• global
• range
• with

The run, in numbers

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Type this snippet

Step 2 of 4 in Threads & processes, step 29 of 53 in Pythonic Python.

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