Opening array from file without knowing its dimensions

[leoyala]

Hello,

I am currently using b2nd_open to open arrays that I created, for which I know its dimensions.
But I recently received some arrays for which I do not know its dimensions, and I was wondering if it is possible to load the NDArrays somehow without knowing its dimensions beforehand. Am I correct that NDArrays do not store any information regarding its shape?

[FrancescAlted]

I don't see why you should know the dimensions prior to open an array. Can you send a small program showing what you are trying to do? (and yes, shape, chunk shape, block shape and the dtype info is stored as metadata; see e.g. "Data types are in!" section in https://www.blosc.org/posts/blosc2-ndim-intro/).

[leoyala]

You are right that I should not need the shape of the data to load the NDArrays, I was confusing how the opening mechanism works.
However, I am in the situation where I am saving images to a file that is initialized as this. While I am doing so, I would like to open a second NDArray (only read) using b2nd_open. Would it be a problem to call blosc2_init only once at the beginning of my program and then use blosc in multiple threads? One thread is responsible for saving the data, while a different one is responsible for reading other files. In the documentation I see that it is mentioned that in multithreaded environments one can use the blosc2_compress_ctx, blosc2_decompress_ctx pair, but I am not sure if calling blosc2_init only once would work instead.

[FrancescAlted]

As long as you are careful and use contexts (e.g. b2nd_create_ctx()) I think you are safe. But the best is always try, and in case something wrong happens, then start to scratch your head (and not before).

[leoyala]

After trying it out for some time, it seems to work to only initialize blosc in the main thread and then use it from other threads. I have not thoroughly test it, but will close this for now as it seems to work :).