Thanks for the response.
I was not aware of the delete operator in JS (I'm still coming up to speed
on some of the languages particulars). So I read up on it and have now
performed a new test to see if:
1) delete will work on a simple numerical variable attribute
2) delete will work on an object (since one definition of the delete
operator suggests that it is designed to clean up objects created with the
'new' operator).
I updated the script slightly (as shown below), the interesting variables
are x and d (x is an instance of a simple numeric variable, d is an instance
of the object goHere created with the 'new' operator).
However, when I run this test I am left with the same problem.
After each line of JS code, I execute System.gc, run Thread.yield(), wait 5
seconds (understanding that System.gc() runs concurrently in another
thread), and write out all variables obtained from the
top_level_scope.getAllIds() method. I can still see the variables "x" and
"d" returned from top_level_scope.getAllIds(), and in fact they still have
their original values (x=1, and d=Object).
In response to your other comments, yes, I would be instantiating a separate
scope per script (following the shared scope model documented on the Rhino
projects page), however in my application a script may execute for a very
long time (on the order of weeks or months), so I need it to be able to
clean up after its self (as well as for some other reasons), relying on
cleanup at the time the scope is discarded isn't enough.
Any thoughts? Thanks!
David
=======
Script
=======
static String js = "var x=1;
" + "\n" + // 1
"delete x;
" + "\n" + // 2
"var y=2;
" + "\n" + // 3
"z=3;
" + "\n" + // 4
"function goHere(a){
" + "\n" + // 5
" var b=5;
" + "\n" + // 6
" c=6;
" + "\n" + // 7
" return (a+b+c);
" + "\n" + // 8
"}
" + "\n" + // 9
"var d = new goHere();
" + "\n" + // 10
"y = null;
" + "\n" + // 11
"var myCars=new Array(\"Saab\",\"Volvo\",\"BMW\");
" + "\n" + // 12
"delete d;
" + "\n" + // 13
"var f = c;
" + "\n" + // 14
"var g=true;
"; // 15
=======
Output
=======
myCars: [EMAIL PROTECTED]
y: [EMAIL PROTECTED]
d: [EMAIL PROTECTED]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: [EMAIL PROTECTED]
At Line #: 1 : var x = 1;
myCars: [EMAIL PROTECTED]
y: [EMAIL PROTECTED]
d: [EMAIL PROTECTED]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 2 : delete x;
myCars: [EMAIL PROTECTED]
y: [EMAIL PROTECTED]
d: [EMAIL PROTECTED]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 3 : var y = 2;
myCars: [EMAIL PROTECTED]
y: 2.0
d: [EMAIL PROTECTED]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 4 : z = 3;
myCars: [EMAIL PROTECTED]
y: 2.0
d: [EMAIL PROTECTED]
z: 3.0
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 10 : var d = new goHere();
myCars: [EMAIL PROTECTED]
y: 2.0
d: [EMAIL PROTECTED]
z: 3.0
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 5 : function goHere(a) {
myCars: [EMAIL PROTECTED]
y: 2.0
d: [EMAIL PROTECTED]
z: 3.0
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 6 : var b = 5;
myCars: [EMAIL PROTECTED]
y: 2.0
d: [EMAIL PROTECTED]
z: 3.0
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
x: 1.0
At Line #: 7 : c = 6;
myCars: [EMAIL PROTECTED]
x: 1.0
y: 2.0
z: 3.0
c: 6.0
d: [EMAIL PROTECTED]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
At Line #: 8 : return (a + b + c);
myCars: [EMAIL PROTECTED]
x: 1.0
y: 2.0
z: 3.0
c: 6.0
d: [object Object]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
At Line #: 11 : y = null;
myCars: [EMAIL PROTECTED]
x: 1.0
y: null
z: 3.0
c: 6.0
d: [object Object]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
At Line #: 12 : var myCars = new Array("Saab", "Volvo", "BMW");
myCars: [EMAIL PROTECTED]
x: 1.0
y: null
z: 3.0
c: 6.0
d: [object Object]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
At Line #: 13 : delete d;
myCars: [EMAIL PROTECTED]
x: 1.0
y: null
z: 3.0
c: 6.0
d: [object Object]
f: [EMAIL PROTECTED]
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
At Line #: 14 : var f = c;
myCars: [EMAIL PROTECTED]
x: 1.0
y: null
z: 3.0
c: 6.0
d: [object Object]
f: 6.0
g: [EMAIL PROTECTED]
goHere: [EMAIL PROTECTED]
At Line #: 15 : var g = true;
myCars: [EMAIL PROTECTED]
* x: 1.0
y: null
z: 3.0
c: 6.0
* d: [object Object]
f: 6.0
g: true
goHere: [EMAIL PROTECTED]
Process finished with exit code 0
-----Original Message-----
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]
a.org] On Behalf Of Norris Boyd
Sent: Monday, November 10, 2008 7:48 PM
To: [email protected]
Subject: Re: Garbage collection of JS variables
On Nov 10, 11:26 am, "David Parks" <[EMAIL PROTECTED]> wrote:
> Hi, I've been playing with the very simple script shown below. I've set up
> an embedded debugger application so I can watch the script execution line
by
> line.
>
> What I have been trying to answer is exactly how garbage collection works
in
> Rhino.
>
> In this example I have defined a variable "x" on line 1, then, on line 2 I
> decide I no longer need the variable, so I set it to null.
>
> At each line of the script, the debugger pauses and I am performing the
> following steps:
> 1) run System.gc()
> 2) this.wait(5000)
> 3) printing out a list of all variables stored in the top-level
> scope
>
> At some point I was hoping that x would be de-allocated (removed from the
> scope), however it never happens, it always remains visible in the top
level
> scope.
>
> What is necessary for a variable to be garbage collected? I will be
> executing a large number of concurrent scripts, and memory is of concern
to
> me.
>
> Thanks!
> David
>
> ______________________________________________________
>
> var x=1;
> x=null;
> var y=2;
> z=3;
> function goHere(a){
> var b=5;
> c=6;
> return (a+b+c);}
>
> var d = goHere(10);
> y = null;
> var f = c;
> var g=true;
>
> ______________________________________________________
>
> Results (with only outputting the value of "x"):
>
> At Line #: 1 : [var x = 1;]
> x: [EMAIL PROTECTED]
> At Line #: 2 : [x = null;]
> x: 1.0
> At Line #: 3 : [var y = 2;]
> x: null
> At Line #: 4 : [z = 3;]
> x: null
> At Line #: 10 : [var d = goHere(10);]
> x: null
> At Line #: 5 : [function goHere(a) {]
> At Line #: 6 : [ var b = 5;]
> At Line #: 7 : [ c = 6;]
> At Line #: 8 : [ return (a + b + c);]
> At Line #: 11 : [ y = null;]
> x: null
> At Line #: 12 : [var f = c;]
> x: null
> At Line #: 13 : [var g = true;]
> x: null
>
> Process finished with exit code 0
> ______________________________________________________
If you want to remove variable "x" from the scope, try "delete x".
Otherwise Rhino must keep "x" defined--people would be surprised if
setting a variable to null resulted in the variable itself
disappearing!
More generally, you'll presumably want to have a different scope for
each script execution. When you're done with each script you can then
release the reference to the scope and the entire scope should be
available for collection.
Thanks,
Norris
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