Re: Java Object allocation from C++ and references?

[Ben Martin <monkeyiq at users dot sourceforge dot net>]

On Wed, 2004-02-04 at 00:40, Andrew Haley wrote:
> Ben Martin writes:
>  > is it correct to assume that if one is to use C++ code and create an
>  > object implemented in Java code, for example, java::lang::String, then
>  > the C++ code creating the new String* does not call delete?
> 
> That's right.
> 
>  > I have rolled rpms for jakarta-lucene using gcj from Fedora
>  > development and using C++ smart pointers to manage
>  > java::lang::string objects seems to work but when I use a C++ smart
>  > pointer on one of the Lucene java objects the program crashes on
>  > the delete of that object.
> 
> You mustn't do that.  Let the garbage collector do the job.

This is initially the way I thought it would work. The only problem that
I saw that led my to question my initial thoughts are how does the JVM
know that the C++ pointer is still required or is not required?

Example
  {
  MyFoo* foo = new mytree::MyFoo();
  MyBar* bar = new mytree::MyBar();
  bar->methodname( foo );
  // at this point foo & bar are "locked" by the C++ code,
  // the GC can not collect them because I still have C++
  // pointers to them and the JVM will have no way of knowing
  // when those pointers drop out of C++ scope on the next code 
  // line so from my understanding the GC can never collect 
  // those objects. If the GC *does* collect them then a dereference
  // of foo or bar which may happen next instead will do very bad   
  // things.
  }

Sorry if this seems a trivial question, but I can't help but think there
are other newbie gcj users who would have the same question.

-- 
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