Circular References in Java

java memory memory-management memory-leaks garbage-collection
Ryan Delucchi picture Ryan Delucchi · Oct 7, 2008 · Viewed 27.8k times · Source

Given an aggregation of class instances which refer to each other in a complex, circular, fashion: is it possible that the garbage collector may not be able to free these objects?

I vaguely recall this being an issue in the JVM in the past, but I thought this was resolved years ago. yet, some investigation in jhat has revealed a circular reference being the reason for a memory leak that I am now faced with.

Note: I have always been under the impression that the JVM was capable of resolving circular references and freeing such "islands of garbage" from memory. However, I am posing this question just to see if anyone has found any exceptions.

Answer

David G picture David G · Oct 7, 2008

Only a very naive implementation would have a problem with circular references. Wikipedia has a good article on the different GC algorithms. If you really want to learn more, try (Amazon) Garbage Collection: Algorithms for Automatic Dynamic Memory Management . Java has had a good garbage collector since 1.2 and an exceptionally good one in 1.5 and Java 6.

The hard part for improving GC is reducing pauses and overhead, not basic things like circular reference.

Related questions

How to set the maximum memory usage for JVM?

I want to limit the maximum memory used by the JVM. Note, this is not just the heap, I want to limit the total memory used by this process.

Read More
Calculate size of Object in Java

I want to record how much memory (in bytes, hopefully) an object takes up for a project (I'm comparing sizes of data structures) and it seems like there is no method to do this in Java. Supposedly, C/C++ has …

Read More
How do I discover memory usage of my application in Android?

How can I find the memory used on my Android application, programmatically? I hope there is a way to do it. Plus, how do I get the free memory of the phone too?

Read More