Subj : Re: [spidermonkey] JS_CallFunction in Finalize
To   : netscape.public.mozilla.jseng
From : Franck
Date : Mon Aug 29 2005 12:26 am


"Brendan Eich" <brendan@meer.net> a écrit dans le message de news: 
det4m6$7o22@ripley.aoltw.net...
> Franck wrote:
>
>> Currently I'm working on a wrapper to libffi ( a kind of JNI for 
>> javascript ).
>> The current state of my project allows me to do such things:
>>
>>   function Alert( text, caption ) {
>>
>>     var ret = new NativeData().PU32.Alloc(1);
>>     new 
>> NativeModule('C:\\WINDOWS\\SYSTEM32\\User32').Proc('MessageBoxA')( ret, 
>> DWORD( 0 ), SZ(text), SZ( caption || "Alert" ), DWORD( 1 ) );
>
>
> BTW, there's no need to require .Proc('MessageBoxA') if you would rather 
> allow just .MessageBoxA instead.
>

I need to do this because I define a 'Close' function on my Module class :/

> Other conversions and explicit helpers could probably also be avoided too, 
> in the interest of readability and economy of expression for your 
> scripting audience.

The only way to do this is to split the call into two steps: one to define 
the prototype and the other for calling the function with arguments.
For the moment I mix them and I use some helpers functions :

function DWORD( value ) {

 var nat = new NativeData().PU32;
 nat.Alloc()[0] = value;
 return nat;
}

function SZ( value ) {

 var nat = new NativeData;
 nat.String = value;
 return nat.PP;
}

function VOID( value ) {

 return new NativeData().VOID;
}

....

>
>
>>     return ret[0];
>>   }
>>
>> The 'Module' class is the one that manages the loaded dll/so file.
>> This class have a 'Close' method and a 'Finalize hook' that both release 
>> the dll/so handler ( if the handler is not released by the user, it is 
>> done when GC is called )
>
>
> Ok.  So far, so good.
>
>
>> Later, I tried to use wxJS with my project. The order of the wxJS use is 
>> important:
>>
>>   load wxJS library;
>>   JS_NewRuntime, JS_NewContext;
>>   wxJS_Init;
>>   JS_ExecuteScript;
>>   wxJS_Destroy;
>>   JS_DestroyContext, JS_DestroyRuntime;
>>   free wxJS library;
>>
>> My first problem is that libraries like wxJS use the SpiderMonkey's API, 
>> so it is not possible to close them at a random ( GC ) time but only 
>> after the context is destroyed.
>
>
> Must you share the same *JSRuntime* with wxJS?

Yes,
In my mind, my library is just a js-side wrapper tool for native DLL, to 
avoid people to write any C/C++ code to make a binding with a DLL.


>
>
>> My second problem is that 'wxJS_Destroy' has to be called before the 
>> context is destroyed.
>>
>> so the only way I found is a kind of 'onClose' property that has to be 
>> defined like this:
>>
>>   function LoadWxJs() {
>>
>>     var libWxJS = new NativeModule('...\\wxJS' );    // .dll/.so
>>     libWxJS.onClose = function() { libWxJS.Proc('wxJS_Destroy')( 
>> VOID() ); };
>>     var ret = new NativeData().PS32.Alloc(1);
>>     libWxJS.Proc('wxJS_Init')( ret, MAKEPTR( JSContextToPtr() ), 
>> MAKEPTR( JSObjectToPtr( this ) ) );
>>   }
>>
>> My wish is that people that use LoadWxJs has not to care about any 
>> 'wxJS_Destroy' ...
>
>
> Since wxJS_Destroy is a native function, you should not expose it and the 
> requirement to call it on your script authors.  I.e., no onClose should be 
> reflected into JS -- on the contrary, you want stronger APIs from wxJS 
> and/or SpiderMonkey to support the mandatory destroy calling protocol.

I know that the best way to use a library like wxJS is to define LoadWxJs() 
and CloseWxJs() functions.
But I want people that use LoadWxJs() (without knowing anything about its 
content) do not have to call CloseWxJs() ( ok, this is sugar !!, a fine 
thing )
When I create a javascript object with new, I do not have to call delete to 
free it ( thanks to the GC )

An other way to do this is to define a global/rooted array of functions that 
are called juste before the context is destroyed. eg :

function LoadWxJs() {
  var libWxJS = new ...
  ...
  onBeforeJS_DestroyContext.push( libWxJS.Proc('wxJS_Destroy')( VOID() ) );
}

But I don't like global things :)


>
> I don't know enough about wxJS to comment further, except to repeat that 
> if you don't need to share objects from its JS engine with yours, then do 
> not use its JSRuntime -- make your own and you should be ok (so long as 
> only one of you calls JS_ShutDown as the very last JS API call before the 
> app exits).

A user of my library use it to load wxJS and use it in its script.
eg.
-- start --
LoadWxJs();
dlg = new wxDialog(null, -1, "Title", wxDefaultPosition, new wxSize( 400, 
400 ));
new wxStaticText( dlg, -1, 'test', wxDefaultPosition, dlg.size, 
wxStaticText.ALIGN_CENTER );
new wxListBox( dlg, -1 );
....
dlg.showModal();
-- end --


>
> /be
>
>

.