ASP JavaScript: Garbage collection algorithm

[Benjamin Johnston]

Hi,

I've found lots of discussion about the JavaScript garbage collector,
but no clear answer to this question:

Is the garbage collection algorithm used in JavaScript on ASP based on
reference counting or tracing?


Thanks for your help,

(I'm planning on creating some user defined Objects with lots of cyclic
references (e.g., a.next.prev = a), and would like to know if this will
cause a problem for the garbage collector. The fact that garbage
collection in general isn't instantaneous suggests to me that it isn't
based on reference counting, but I just want to be sure.)

(I'm NOT using ASP.NET... just plain old ASP... if this is relevant)

-Benjamin Johnston

 

[Bob Barrows [MVP]]

Hi,

I've found lots of discussion about the JavaScript garbage collector,
but no clear answer to this question:

Is the garbage collection algorithm used in JavaScript on ASP based on
reference counting or tracing?

There's nothing better than Eric Lippert's blogs on this subject:
http://blogs.msdn.com/ericlippert/
Specifically:
http://blogs.msdn.com/ericlippert/archive/2003/09/17/53038.aspx
http://blogs.msdn.com/ericlippert/archive/2004/04/28/122259.aspx

(I'm planning on creating some user defined Objects with lots of
cyclic references (e.g., a.next.prev = a), and would like to know if
this will cause a problem for the garbage collector.

Probably. Read what Eric has to say about closures.
http://blogs.msdn.com/ericlippert/archive/2003/09/17/53028.aspx

 

[Benjamin Johnston]

/snip/
http://blogs.msdn.com/ericlippert/archive/2003/09/17/53038.aspx
http://blogs.msdn.com/ericlippert/archive/2004/04/28/122259.aspx

Fantastic, thanks a lot! This is exactly what I was looking for.


For the benefit of other readers and future readers searching the
archives, I'll summarize:

JavaScript in ASP uses a mark-and-sweep tracing garbage collector, so
it is okay to have cyclic **user-defined** data structures.

However, the garbage collector can't detect cycles involving
non-JavaScript objects (such as mixed VBScript and JavaScript, or
built-in objects, or COM objects); so such cycles will not be garbage
collected.

Also, it should be noted that this only applies to JavaScript, VBScript
uses a different garbage collector that doesn't handle cycles.

-Benjamin Johnston