Subj : Memory management of contexts etc.
To   : netscape.public.mozilla.jseng
From : Heath Raftery <hraftery@myrealbox.com>
Date : Tue Sep 23 2003 11:54 pm

Hi,

Not long ago folks on this newsgroup saved my sanity but helping me out 
in writing a PAC file parser using SpiderMonkey. It is all working great 
(woohoo!), but I've got some followup questions about style and proper 
contex management.

My code structure looks like this:

<CODE>
main()
{
  daemon(0, 0);

  JSFunction* compiled = compile(arg1)
  
  for(;;)
  {
    switch(fork())
    {
      case 0:
        result = execute(compiled, arg2)
        /* act on result */
        break;
    }
  }
  JS_DestroyRuntime(rt);
}

JSRuntime *rt;
JSObject *global;
JSClass global_class =
{
  "global", 0, 
JS_PropertyStub,JS_PropertyStub,JS_PropertyStub,JS_PropertyStub,
  JS_EnumerateStub,JS_ResolveStub,JS_ConvertStub,JS_FinalizeStub
};

JSFunction* compile(arg1)
{
  JSContext *cx;

  rt = JS_NewRuntime(1L * 1024L * 1024L);
  cx = JS_NewContext(rt, 4L * 1024L);
  global = JS_NewObject(cx, &global_class, NULL, NULL);
  JS_InitStandardClasses(cx, global);

  JSFunction *compiledFunc = JS_CompileFunction(cx, global, ...);

  //***can't do this here***
  //JS_DestroyContext(cx);

  return compiledFunc;
}

char* execute(JSFunction *compiledScript, const char *arg2)
{
  JSContext *cx;
  cx = JS_NewContext(rt, 4L * 1024L);

  JS_CallFunction(cx, global, compiledScript, 2, args, &rval);
  str = JS_ValueToString(cx, rval);
  
  JS_DestroyContext(cx);
  
  return JS_GetStringBytes(str);
}
</CODE>

Now, note that I can't destroy the context in compile(), because the 
function will then fail to run in execute(). Thus, I never actually get 
the chance to destroy it! Is this particularly undesirable?

Is my basic runtime/context use scheme flawed? It seems to run fine, but 
I haven't done any intense analysis of memory use or profiling. There 
does appear to be a bit of a pause (a couple of seconds) while the 
compiled function is executed, but not knowing how long the script 
should take to execute in the first place, it is a bit hard to nail down 
a bottleneck.

Appreciate any comments.
Heath

-- 
Heath
 ________________________________________________________
| *Nothing is foolproof to a sufficiently talented fool* |
|                                         _\|/_          |
|________________________________________m(. .)m_________|

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