hi
this is a very helpful metaphor, I can read your C-calling-Lua example
and then get the C-calling-Javascript like i was reading a tutorial,
thank you.
One question, and this is not about calling C-calling-JS, it is about
calling JS-calling-C
In AlchemyDB, in C, I have the following line
lua_register(Lua, "client", luaCall_client);
Which tells the Lua interpreter, that when a lua scripts makes a
"client()" call, it should be rerouted to my C function
"luaCall_client()".
Is there a similarly simple mechanism to register JS functions to call
defined C functions.
This is the part I am not yet fully grasping on how to code it :)
- Jak
On Jan 18, 8:08 am, Vyacheslav Egorov <[email protected]> wrote:
> Jak,
>
> I think it would be pretty easy to convert your Lua intergration into
> V8 intergration line by line without relying on any third party
> libraries.
>
> Let me show you a mapping between Lua and V8 APIs
>
> Lua:
> // Lua API manipulates with stack. Anything on the stack will be kept
> alive when GC happens.
> int code = luaL_dostring(L, s);
> if (code) {
> // error is on top of the stack
> const char *error_message = lua_tostring(L, -1);
> report(error_message);} else {
>
> // return values are on top of the stack
>
> }
>
> V8:
> // V8 does not have implicit stack. Instead API is all about Handles.
> // Handles keep what they reference alive during GC.
> // There are two types of the Handles: Local and Persistent.
> // Each Local handle is owned by a HandleScope --- when HandleScope
> dies so do all Local handles it owns.
> // In terms of Lua: creating HandleScope is like remembering height of
> Lua stack, creating Local handle is like pushing
> // value on the stack and destroying HandleScope is like poping
> everything above remembered height.
> v8::HandleScope handle_scope;
> Local<String> v8_string = v8::String::New(s);
> Local<Script> script = v8::Script::Compile(v8_string);
> v8::TryCatch try_catch;
> Local<Value> result = script->Run();
> if (try_catch.HasCaught()) {
> // exception is in try_catch.Exception()
> v8::String::AsciiValue error_message(try_catch.Exception());
> report(*error_message);} else {
>
> // returned value is in the result.
>
> }
>
> As you can see conversion is pretty much straighforward.
>
> --
> Vyacheslav Egorov
>
> On Tue, Jan 18, 2011 at 4:35 PM, Jak Sprats <[email protected]> wrote:
> > Hi Stephan,
>
> > this is very helpful, so thank you.
>
> > I am going to explain my use-case fully, because its pretty easy once
> > explained, (I am a bad explainer) and forgive me if my explanations
> > are overly simplistic, I am just a fanatic on clarity, so I write
> > things as dumbed down as possible.
>
> > A.) AlchemyDB has SQL commands
> > 1.) SELECT * FROM tbl WHERE user_id = 33 AND name = 'sally'
> > 2.) UPDATE tbl SET count = count + 1 WHERE id = 1234
> > B.) AlchemyDB has redis commands
> > 1.) SET session_77 'name:bill;age:22'
> > 2.) HGET user_77 name
> > C.) AlchemyDB currently has some commands to call the embedded LUA
> > This will add the file "functions.lua" to the embedded lua
> > environment (used to populate lua libraries)
> > 1.) CONFIG ADD LUA functions.lua
> > This will pass the string 'return 1*2*3' to the embedded lua parser/
> > executor which will perform the action '1*2*3' and pass the results
> > back to AlchemyDB
> > 2.) LUA 'return 1*2*3;'
> > This will call AlchemyDB's SQL and Redis commands from w/in LUA
> > First the session is checked for existence, and if it exists all
> > rows from the table 'user_data' are returned, otherwise return an
> > empty-string
> > 3.) LUA 'sess = client('GET', 'session_77'); if (sess == nil)
> > return "" else return client('SELECT','*','FROM',;user_data', ' WHERE
> > id = 77'); end'
>
> > The lua function "client()" makes internal calls to AlchemyDB's SQL
> > and redis commands, and is VERY useful for avoiding network hops, and
> > placing trivial logic datastore side. Its like a sane stored
> > procedures implementation.
>
> > I want to have the exact same thing in Javascript, because Javascript
> > is really gaining in momentum, has 1000s of good libraries, and
> > Node.js's Alchemy users would backflip at the possiblity of
> > arbitrarily doing javascript logic at any point in their architecture.
>
> > So I need a very lightweight embedding of V8 and the single javascript
> > function "client()" that can call C to internally reach into
> > AlchemyDB.
>
> > I can have options to make AlchemyDB in C++ to be able to include V8,
> > that is acceptable.
>
> > I understand everything you wrote, I am just a little bit leery of how
> > much time it will take to figure out all the finer details of
> > embedding one language in another in another, it was actually tricky
> > to do w/ Lua, and lua is made for embedding ease. Any idea how many
> > man-days embedding V8 and then using v8-juice to implement the JS func
> > "client" would take? (just ballpark: is it a day, a week, a month?)
>
> > What would be REAL helpful is if there was a hello-world for embedding
> > v8 in C and then using v8-juice to define a hello-world JS-calling-C
> > function along w/ a how to compile and test for dummies, so I could
> > start playing around w/ it. This is my work style, if I can build
> > something, I can start glueing things together, but this initial
> > learning curve of libraries internals/peculiarities takes me a long
> > time.
>
> > thanks,
> > Jak
>
> > On Jan 17, 7:10 am, Stephan Beal <[email protected]> wrote:
> >> On Mon, Jan 17, 2011 at 2:51 PM, Jak Sprats <[email protected]> wrote:
> >> > This seems to be what I am looking for ... some questions:
> >> > 1.) AlchemyDB is written in ANSI-C, what are the requirements for your
> >> > bindings (C++ at a minimum, any specifics on that)
>
> >> Whatever requirements v8 has, basically. i don't remember v8-juice have any
> >> requirements above what v8 needs.
>
> >> > 2.) I just need one function wrapped, the function is called
> >> > "client()" and it can take between 1 and 6 arguments.
>
> >> The code demonstrated on that page accepts up to 10 arguments, and more can
> >> be generated via a script.
> >> You don't need all of v8-juice for what you're doing: you can get by with
> >> only some of the header files:
>
> >> Go
> >> to:http://code.google.com/p/v8-juice/source/browse/#svn/trunk/src/includ...
>
> >> grab:
>
> >> - convert.h
> >> - forwarding.h
> >> - forwarding-*.h (generated code)
> >> - TypeList.h
> >> - TypeList_*.h ( generated code)
>
> >> And that should do it. The primary advantage, over using the whole v8-juice
> >> lib, is that you need only headers, not .cpp files. All of the type
> >> conversion/function-forwarding code is templates, and implemented in their
> >> header files.
>
> >> Your code should include convert.h and/or forwarding.h, and the rest are
> >> implementation details. Those files assume an includes path of
> >> <v8/juice/foo.h>, and you will need to replace those if you plan to use a
> >> different structure.
>
> >> > And on a long shot, do you know of any C programs that embedded V8 and
> >> > then the embedded v8 calls a C function via your bindings. This is
> >> > what I am trying to reproduce in AlchemyDB (the C function would be
> >> > "client()").
>
> >> i don't know of any programs which reach into v8 from C. i have implemented
> >> v8 add-ons on top of C libraries (like libcurl and libsqlite3), but that's
> >> going the other direction. C cannot call directly into JS because it can't
> >> use the objects needed by v8. It can, of course, use a C++ API which has
> >> been wrapped in (extern "C" {...}), which then can pass on the calls to v8.
> >> So the call chain would look like: C -> C++ -> JS
>
> >> i hope this helps a bit,
>
> >> --
> >> ----- stephan bealhttp://wanderinghorse.net/home/stephan/
>
> > --
> > v8-users mailing list
> > [email protected]
> >http://groups.google.com/group/v8-users
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