Subj : Re: SpiderMonkey's Funky GC and me
To   : netscape.public.mozilla.jseng
From : Alex
Date : Wed Mar 23 2005 07:20 pm


"Brendan Eich" <brendan@meer.net> a écrit dans le message de
news:d1sat0$go1@ripley.netscape.com...
> Alex wrote:
> > well
> >
> > I have this script:
> >
> > var strdef      = "psittacisme ?";
> > var intdef      = 42;
> > var dbldef      = 8.6;
> > var truedef     = true;
> > var falsedef    = false;
> >
> > if i run my script, invoke the gc system and try to get dbldef's value,
i
> > get an int (under linux), or a string (under solaris).
>
>
> What do you mean by try to get dbldef's value?
>
> What code do you use to run the script, and what keeps the object in
> which these variables are defined alive across the GC?
>
> /be

Well, here is a summary of the code:

***********************************************
JSClass g_globClass = {
    "GlobalObj",                 //Class Name
    0,                           //flags
    /* Mandatory non-null members. */
    JS_PropertyStub,             //add
    JS_PropertyStub,             //del
    JS_PropertyStub,             //get
    JS_PropertyStub,             //set
    JS_EnumerateStub,            //enumerate
    JS_ResolveStub,              //resolve
    JS_ConvertStub,              //convert
    JS_FinalizeStub,             //finalize
    /* Optionally non-null members.*/
    NULL,                        //getObjectOps
    NULL,                        //checkAccess
    NULL,                        //call
    NULL,                        //construct
    NULL,                        //xdrObject
    NULL,                        //hasInstance
    NULL                         //spare (reserved for future use.)
};


    m_Runtime = JS_NewRuntime(0x400000L);
    if (m_Runtime)
        return EXT_JS_INIT_ERROR;

    m_Context = JS_NewContext(m_Runtime, 8192);
    if (!m_Context)
         return EXT_JS_INIT_ERROR;

    m_GlobalObj = JS_NewObject(m_Context, &g_globClass, 0, 0);
    if (m_GlobalObj)
        return EXT_JS_INIT_ERROR;

    if (!JS_InitStandardClasses(m_Context, m_GlobalObj))
        return EXT_JS_INIT_ERROR;

    JS_SetErrorReporter(m_Context, ErrReporRef); // ErrReporRef is an error
reporting fun...

    //m_ScriptArray is an array of compiled script (we are meant to use more
than only one)
    for (int i = 0; i < SCRIPTNBR; i++)
        m_ScriptArray[i] = NULL;

    JSFunction * PrintPtr = JS_DefineFunction(m_Context,

m_GlobalObj,

"print",
                                                                      print,
                                                                      1,
                                                                      0);
    if (!PrintPtr)
        cerr << "Oop" << endl;

    char * lscriptBuff = getScript(a_path);
    JSScript *lscript = JS_CompileScript(m_Context, m_GlobalObj,
lscriptBuff,

strlen(lscriptBuff),
                                                              a_path,
                                                              0);
    m_ScriptArray[42] = lscript;

    jsval vp;
    JSBool lJSResult = JS_ExecuteScript(m_Context, m_GlobalObj,

m_ScriptArray[a_scriptIdx], &vp);
    JS_GC(m_Context);

    jsval rval;
    lJSResult = JS_GetProperty(m_Context,
                                                m_GlobalObj,
                                                "dbldef",
                                                rval);
    if (lJSResult != JS_TRUE)
        return EXT_JS_INTERNAL_ERROR;

***********************************************

after this, i though i could have access to the variable used by the script
mentionned earlyer, but...

Another funky trick is this:

if i have a javascript file containing:
*********************
print("Wizz !!\n");
*********************

and if i use the garbage collector before executing the script
(JS_ExecuteScript), my print function receive a null pointer as the string
to print.

Thanks for interesting in my trouble

(And sorry for the pure frenchy grammar...)

.