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> The standard library has lists and dictionaries, which are not thread-safe to access from two threads simultaneously, and are not in any way locked. Locking

by exDM69 11y ago

> The standard library has lists and dictionaries, which are not thread-safe to access from two threads simultaneously, and are not in any way locked. Locking lists and dicts, etc would not be a reasonable thing to do. There must be some granularity in synchronization, it's clearly not a good idea to attempt to allow mutating any object from multiple threads without explicit locking. Things like readline are issues that programmers have to deal with when writing multi threaded code in any language. There are libs which are not thread safe or which have global state or need special handling with threads (e.g. OpenGL). That's no reason to disallow threading completely. However, this might be a big culture shock issue if Python were to suddenly start supporting proper concurrency without GIL. None of the libraries document whether they are thread safe or not, so there would be surprises ahead.

Erwin 11y ago
Locking the basic data structures seems like it would destroy Python's simplicity. How do you determine the scope of the per-list lock? Do you add a lock to every single data structure that you are required to grab before reading or modifying it? If you require the programmer to do it, you can easily get race conditions which will only show up once in a blue moon causing incorrect results or corruption at worst - something Python's GIL guaranteed not to happen (as long as you didn't do anything risky in your C extension). Is there any solution that doesn't use purely functional data structures?
JoshTriplett 11y ago
That's exactly why the approach proposed in this article potentially makes sense: run independent interpreters in different threads, and make all data sharing explicit. Then, anything shared between threads will need to know how to handle that, and anything that doesn't advertise that it's safe to share gets a lock around its use.

by exDM69 11y ago

Erwin 11y ago

Locking the basic data structures seems like it would destroy Python's simplicity. How do you determine the scope of the per-list lock? Do you add a lock to every single data structure that you are required to grab before reading or modifying it? If you require the programmer to do it, you can easily get race conditions which will only show up once in a blue moon causing incorrect results or corruption at worst - something Python's GIL guaranteed not to happen (as long as you didn't do anything risky in your C extension). Is there any solution that doesn't use purely functional data structures?

JoshTriplett 11y ago

That's exactly why the approach proposed in this article potentially makes sense: run independent interpreters in different threads, and make all data sharing explicit. Then, anything shared between threads will need to know how to handle that, and anything that doesn't advertise that it's safe to share gets a lock around its use.