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matklad / once_cell

Rust library for single assignment cells and lazy statics without macros
Apache License 2.0
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Add sync::OnceCell::prev_init_panicked method #89

Closed pitdicker closed 2 years ago

pitdicker commented 4 years ago

I am interested about your opinion about an prev_init_panicked method (not attached to the name).

If we don't want to give guarantees about side effects, it is not possible to implement poisoning with user code. Even sync::Lazy relies on side effects to synchronize its Cell<Option<F>>.

I still think it is the right choice to have OnceCell act as if there is no poisoning in the common case is a good default, as it matches what you care about: initialization, not upholding some variant as running exactly once.

For std the changes to the implementation are minimal.

For the parking_lot implementation I had to go with the same pattern to use a finalizer that sets the appropriate state on panic/err/success. To keep the size of OnceCell the same as before, I used an AtomicU8 which bumps the MSRV for the parking_lot feature to 1.34.

matklad commented 4 years ago

:scream: don't have time to look into this, but, in general, I would prefer to just defer the poisoning decision to t-libs, as I have zero intuition where it is useful and where it is not