HDF5.jl: How to write type stable code

General Usage
1

Hi, I was wondering how to write type stable code using HDF5 files. I Have code that looks like this

getMyArray(filename::String) = hdfread(filename,"/myArray")

So if I know that the array is of type Float64 and has three dimension is it sufficient to write

getMyArray(filename::String)::Array{Float64,3} = hdfread(filename,"/myArray")

Or can I do any better?

1 Like
2

I think that is the correct way of doing it.

3

Ok thanks! And how “bad” is that hdfread is still type unstable? I think there are functions that allow to preallocate the array making things potentially type stable. I would like to know if this is worth investigating or if my code is fine an I won’t gain anything.

4

I think the HDF5.jl package is still a work in progress. A great deal works but I’m currently stuck on how to append data, writing variable length strings, and how to make compound tables and fill them.

5

yes, there are some remaining pieces in HDF5.jl but my question is actually not that tight on that lib. Any IO reader will have this issue I described above.

6

It’s not really a problem that hdfread is type unstable because the time to do the type assert should be completely insignificant compared to the time it takes to execute hdfread

7

Not sure I understand. My issue is that I have several of these hdfread in my code and the first time I call it needs 1.7 seconds, the second requires 0.004762 seconds.

In the end I don’t personally care about type stability in this case. But I had the impression that type stable code is easier to compile (i.e. infer).

8

I didn’t know we were talking about compilation time… I haven’t gotten the impression that type stable code is faster to compile. In some sense, shouldn’t it be slower since you can do more optimizations with type stable code?

9

Yes sorry. That is the question I asked in Does compile time depend on type stability - #3 by tobias.knopp

My global issue is that the UI application I am working on is not usable if it requires 2 minutes to start up and pressing a button the first time requires 20 seconds. Since pressing a button involves reading e.g. HDF5 file I was wondering if it would be a good idea to “clean up” the type unstable low level code in order to make my application start faster.