Re: finalize() allowed to be called before constructor finishes?

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 20 Apr 2007 16:22:06 -0700

Message-ID:

<f0bhv6$2t96$1@ihnp4.ucsd.edu>

Boris wrote:

Is there any guarantee that finalize() is called only after a
constructor finishes? I wonder as the documentation at
http://java.sun.com/javase/6/docs/api/java/lang/Object.html#finalize()
says that the "Java programming language does not guarantee which thread
will invoke the finalize method".

I ask as I have a Java class which makes two JNI calls in the
constructor. In finalize() another JNI call is made to release
resources. If the class is instantiated thousands of times in a loop
without storing references I get an exception or crash at some point as
the second call in the constructor tries to use a resource which
strangely has been released already. If I change the program and store
references to make sure that the garbage collector releases all objects
only after the loop everything works fine. I'm now trying to understand
if there is a race condition as the second JNI call in the constructor
doesn't see the resource sometimes. Any ideas?

I'm assuming you do not have any explicit finalize() calls in the
constructor.

According to the JLS "The completion of an object's constructor
happens-before (?17.4.5) the execution of its finalize method (in the
formal sense of happens-before)."

[12.6 Finalization of Class Instances,
http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.6]

I would start looking for exactly what resource is involved, and how
actions involved in it are synchronized.

Patricia