Skip to main content

Garbage collection in Java

I am starting a series of posts on the Java garbage collector and various garbage collection algorithms. Over the 10 days or so, we will examine the Java garbage collector and garbage collection algorithms. Let's begin with a brief introduction.

An executing program occupies memory. Memory is taken as new objects are created. This memory should be returned when these objects are no longer needed. If it is not, then the computer will soon run out of resources, forcing the program to a halt. In C++ we have to explicitly return an object's memory back to the system when the object is destroyed. This is also the source for many bugs in C++. Buggy code that does not return memory can very soon exhaust system resources. To eliminate such errors, and make your program more robust, Java has adopted the philosophy of automatic memory reclamation. The JVM determines when an object is no longer needed (Eg: after the variable goes out of scope), and automatically reclaims memory occupied by that object. Objects no longer needed are known as 'garbage', because; well that is what we call things we no longer need, right? Hence reclamation of un-needed heap (Java objects are always created on the heap) memory is known as garbage collection in Java.

The JVM runs the garbage collector as a background thread, which constantly monitors the heap. The exact mechanism of reclaiming memory is JVM specific. The Java Language Specification (JLS) does not mandate any particular mechanism for garbage collection, hence it is implemented by the JVM creator.

There are several well known garbage collection algorithms that are implemented by modern JVM's. Each has pros and cons in terms of memory usage and performance. Some of these algorithms are:

  • Reference counting algorithms

  • Tracing algorithms

  • Compacting algorithms

  • Copying algorithms

  • Generational algorithms

  • Adaptive algorithms

In the next post we will discuss "Reference counting algorithms"

Discuss this post in the learning forum.

Commercial Links

Labels:

Comments

Post a Comment

Popular posts from this blog

Fuctional Programming Principles in Scala - Getting Started

Sometime back I registered for the Functional Programming Principles in Scala , on Coursera. I have been meaning to learn Scala from a while, but have been putting it on the back burner because of other commitments. But  when I saw this course being offered by Martin Odersky, on Coursera , I just had to enroll in it. This course is a 7 week course. I will blog my learning experience and notes here for the next seven weeks (well actually six, since the course started on Sept 18th). The first step was to install the required tools: JDK - Since this is my work machine, I already have a couple of JDK's installed SBT - SBT is the Scala Build Tool. Even though I have not looked into it in detail, it seems like a replacement for Maven. I am sure we will use it for several things, however upto now I only know about two uses for it - to submit assignments (which must be a feature added by the course team), and to start the Scala console. Installed sbt from here , and added the path
1 comment
Read more

Five Reasons Why Your Product Needs an Awesome User Guide

Photo Credit: Peter Merholz ( Creative Commons 2.0 SA License ) A user guide is essentially a book-length document containing instructions for installing, using or troubleshooting a hardware or software product. A user guide can be very brief - for example, only 10 or 20 pages or it can be a full-length book of 200 pages or more. -- prismnet.com As engineers, we give a lot of importance to product design, architecture, code quality, and UX. However, when it comes to the user manual, we often only manage to pay lip service. This is not good. A usable manual is as important as usable software because it is the first line of help for the user and the first line of customer service for the organization. Any organization that prides itself on great customer service must have an awesome user manual for the product. In the spirit of listicles - here are at least five reasons why you should have an awesome user manual! Enhance User Satisfaction In my fourteen years as a
Post a Comment
Read more

Inheritance vs. composition depending on how much is same and how much differs

I am reading the excellent Django book right now. In the 4th chapter on Django templates , there is an example of includes and inheritance in Django templates. Without going into details about Django templates, the include is very similar to composition where we can include the text of another template for evaluation. Inheritance in Django templates works in a way similar to object inheritance. Django templates can specify certain blocks which can be redefined in subtemplates. The subtemplates use the rest of the parent template as is. Now we have all learned that inheritance is used when we have a is-a relationship between classes, and composition is used when we have a contains-a relationship. This is absolutely right, but while reading about Django templates, I just realized another pattern in these relationships. This is really simple and perhaps many of you may have already have had this insight... We use inheritance when we want to allow reuse of the bulk of one object in other
3 comments
Read more