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/
>
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