Re: [Caml-list] In-memory assembly

[Basile Starynkevitch <basile@starynkevitch.net>]

On 01/10/2018 11:20 AM, Christoph Höger wrote:
> Dear all,
>
> I want to trigger OCaml compilation programmatically from a C++ 
> application and avoid the usage of subprocesses. It is fairly 
> straightforward to generate an OCaml AST, but I cannot compile it.


You should explain what kind and size is the generated code, and why do 
you want to avoid the usage of subprocesses.
My impression is that you should not be afraid of using subprocesses and 
temporary files.

Some hints and feelings (which I did not got from generating Ocaml code, 
but C code, in my past http://starynkevitch.net/Basile/gcc-melt/ project)


Generating Ocaml code is a good idea (I am very fond of metaprogramming 
in general). Perhaps you should into MetaOcaml (see 
http://okmij.org/ftp/ML/MetaOCaml.html for more)

I'm guessing you might generate a non-tiny amount of Ocaml code, and 
since you want to use the native Ocaml compiler, that code will run for 
a non-short period of time. Notice that if both assumptions are false 
(tiny amount of generated code, running for a short period of time) 
you'll be happy by embedding the Ocaml bytecompiler in your C++ 
application (and there is no real point in using the native Ocaml 
compiler), which I believe is a solved problem.

So, I am assuming you generate a non-small Ocaml file (e.g. a thousand 
lines), and it runs for a non-tiny amount of time (e.g. at least half a 
second, or perhaps 0.1 second).

Then you probably want to ask your ocamlopt compiler to optimize, e.g. 
with its -O2 flag. This probably takes a few tenths of seconds (on a 
file of a few thousand lines of Ocaml), or more. That delay (even 0.1 
seconds of compilation time by ocaml) is long enough to make the usage 
of subprocesses insignificant: a modern system can run hundreds of 
processes every second.

If you care about filesystem delays (which are not that important), 
consider putting the generated Ocaml source code on some fast 
filesystem, e.g. some tmpfs on Linux.

Cleaning up temporary files and running short processes from C++ code is 
a solved problem (and a very common practice).

Cheers.


Basile STARYNKEVITCH   == http://starynkevitch.net/Basile
opinions are mine only - les opinions sont seulement miennes
Bourg La Reine, France