Making Randomizable transform threadsafe by having randomize() return the required random value

[RomStriker]

Hi,

For context, I am using CacheDataset with ThreadDataloader. I have a random transform class CustomTransform(Randomizable, Transform) which inherits from both Randomizable and Transform. In the documentation for Randomizable it says "This API is not thread-safe.".

I noticed that the abstract randomize() method of Randomizable does not return anything and in examples it is used only to update class attribute randomly, which can then be used further. This I assume could be a problem when used with a ThreadDataloader, since a different thread might update the random class attribute before the main thread can use the previous value of the class attribute.

I thought I could solve this by making the randomize() method return the random value instead of storing it in a class attribute and using it directly. Would this approach make this Randomizable transform threadsafe? Maybe there is some aspect of randomness that I am missing.

Also, is there some simple way of making Randomizable methods threadsafe? In the documentation for Transforms, it mentions "When used from a multi-process context, transform’s instance variables are read-only. thread-unsafe transforms should inherit monai.transforms.ThreadUnsafe." What does this mean?

Any comments would be appreciated.

[wyli]

thanks for looking into this, in some use cases we want to generate the randomised factor once and apply it across different modalities/image-label pairs consistently, the class attributes are used to synchronise these..

[RomStriker]

Okay, thanks. Do you think returning the randomised factor if I only need to use it once makes it thread-safe?

[wyli]

Yes, I think that'll be thread-safe.