[Animats]

Yes. I once discovered that CPickle was not thread-safe. The response was that much of the library didn't really work in multi-threaded programs.

[formerly_proven]

You mean programs where you put an object into pickle and some other threads modify it while pickle is processing it? Doesn't surprise me - the equivalent written in plain Python would be very thread unsafe as well.

[Animats]

No, I mean several threads doing completely separate CPickle streams with no shared data or variables at the Python level.

[kzrdude]

Has it since been fixed?

[toyg]

Probably not. CPickle is famously shunned by anyone who has to do serious, performance-critical serialization/deserialization.

[kzrdude]

I was curious, and an issue that fits the description was fixed in Py 3.7.x here: https://bugs.python.org/issue34572 but other threading bugs remain: https://bugs.python.org/issue38884

[azinman2]

What’s the most performance critical alternative? Pickle is tied to the VM, so it’s not a generally good persistence option in a prod setup, but it can mighty convenient.

[garmaine]

What do people use instead?

[da39a3ee]

JSON, protocol buffers, thrift, etc. Saving python-native objects such as functions, class instances etc is usually not the right thing to do in production code.