Export deserialize_json at the C++ level in addition to R

[eddelbuettel]

As seen in #79 there is interest in hitting the deserialize_json() workhorse function directly. (It was also seen that exporting it at the R level brings neglible gains while adding a documentation / test / maintenance burden -- fparse() is still the recommended venue.)

However we can make it available at the C level and the (currently new) branch feature/export_c_level does this. To use it, please

• add a LinkingTo: directive in the client package, and include the header RcppSimdJson.h to access _deserialize_json()
• add an Imports: and import any R symbol (to force instantiation so that R becomes aware of the C-callable symbol.

That should do the trick. @shikokuchuo let us know if this works for you. We could help with a more explicit example if need be.

[shikokuchuo]

Thanks for putting this together so quickly! I can confirm that it works fine mechanically. I will update you on the benefits once I get a chance to test it next week.

[eddelbuettel]

Excellent. It's a good mechanism we all should probably use more, at least for some things.

My recent experience is quite good with another package pair of mine. So I probably roll this out here for RcppSimdJson, and this would be no change for you as you just need a minimum version larger than current CRAN. So I may bump this to CRAN anyway. But no rush, I can (and maybe should) also wait for some first actual feedback from you. It may be a nice boost for repeated calls.

[eddelbuettel]

Closed by #80

[shikokuchuo]

Wow you were quick to get this to CRAN! Luckily I find that the LinkingTo solution works as expected and I can make it ever so slightly faster than simply exporting .deserialize_json(). In terms of what I'm experiencing, compared to fparse() , reading JSON is now c. 8% faster on a typical payload. But in terms of high frequency updates of c. 300-500 bytes each the run time is reduced to 1/5 (<4 microseconds!).

[eddelbuettel]

I was on a roll yesterday and cleaned a few things up, including an upstream update and a quick detail check with @lemire.

Are you using it from ichimoku on 'frequent small parses'? Then the direct, C-level call will help on both fronts. Maintaining the normal interface is still better for more standard usage patterns, so all good.

[shikokuchuo]

I am reading from websockets, not an ideal setup but out of my control! Not ichimoku, but as it's all nicely on CRAN now, I will update that package to use the new mechanism. Thanks again!

[shikokuchuo]

FYI this is the commit that implements this for package 'ichimoku': shikokuchuo/ichimoku@702025

Hope this is a helpful reference in case others want to do the same.

Of course the real power comes from being able to call it from C code as you rightly identify. But that's for another day / something else...

[eddelbuettel]

Small world. I did the same for xts (in the older, more mechanical way; for RcppSimdJson it is basically automated thanks to Rcpp) so good to see it pop up too :)