Re: [Pharo-dev] [NativeBoost] Calling a function in a struct

2015-02-22 0:06 GMT+01:00 Max Leske <maxleske@gmail.com>:

Hi.

I have a situation with libgit2 where the function I need to call is a field in a struct (the field gets populated with different functions with the same signature depending on certain conditions).

I’m facing two problems now: 1. how do I define a function as the field type of an NBExternalStructure?

Athens creates a structure with callbacks as a surface plugin for the bitblter (SQSurfaceDispatch). But this is a structur with functions (generated with NB) that are called "from the outside"

2. how can I call the function?

I don't know of any example in the image, where we are calling a function defined in a struct. Maybe you can extend NBFFICallout to generate a call from a function spec + function address NBFFICallout>>#generateCall:module: does this, it generates a call from a function spec and and address loockuped in a module, maybe you can do something similiar, but use the function address from the structure isntead of calling nbGetSymbolAddress:module:

I’ve tried using callbacks as field types. That works as far as I can access the functions by pointer. But how would I then call that function? I’ve looked at NBNativeFunction and NBNativeFunctionGen but I can’t see how I should use either of those to make a plain call.

Here’s a more precise description of my problem:

writepack := LG2GitOdbWritepackS new. … “initialize the struct externally”

“now call the function ‘commit’ and pass the arguments (this is how I imagine it could work…)" writepack commit value: writepack value: anotherStruct.

Needed struct fields:

backend: git_odb_backend * append: int (*)(git_odb_writepack *, const void *, size_t, git_transfer_progress *) commit: int (*)(git_odb_writepack *, git_transfer_progress *) free: void (*)(git_odb_writepack *)

For what is this needed? Do you want to write your own git backend? I find this strange. I only know of two use cases for function pointers in a structs. 1. to define the callbacks (like athens does it for the SQSurfaceDispatch). But we only define the functions and don't call them. 2. a library defines a public api and delegates the implementation to different backends, but structure and backend functions are hidden. Users of the library don't call them.

My current (ad hoc) struct fields:

fieldsDesc ^#( LG2GitOdbO backend; LG2WritePackAppendCb append; LG2WritePackCommitCb commit; LG2WritePackFreeCb free; )

I’d even be happy if I have to implement a method on LG2GitOdbWritepackS for every function call (e.g. “writepack commit: arg1 and: arg2”) but how would I make the call?

Any ideas? Max