bpo-41735: Fix thread locks in zlib module may go wrong in rare case.

[ghost]

https://bugs.python.org/issue41735

[iritkatriel]

Can you add a unit test that fails without the fix and passes with it?

[ghost]

Can you add a unit test that fails without the fix and passes with it?

Run this code:

import zlib import threading with open('txt.tar', 'rb') as f: b = f.read() b = b[:100*1024*1024] print('read', len(b)) cobj = zlib.compressobj() def f(name, cobj, b): print(name) dat = cobj.compress(b) print(name, len(dat)) thread1 = threading.Thread(target=f, args=('T1', cobj, b)) thread2 = threading.Thread(target=f, args=('T2', cobj, b)) thread1.start() thread2.start() print('ok')

Before the patch, output:

read 104857600 T1 T2 ok T1 57142315 

It seems thread2 did not finish the compressing.

After the patch, output:

read 104857600 T1 T2 ok T1 57165411 T2 57166659 

[ghost]

Can you add a unit test that fails without the fix and passes with it?

Seems a little troublesome. If the data is large, it may be time-consuming. If the data is small, it may not trigger the bug.

Above code can reliably reproduce the bug.

[bedevere-bot]

@ambv: Please replace # with GH- in the commit message next time. Thanks!