Insert-Contended-Into-Class-File

Insert @Contended annotation into Java class files

Introduction

@Contended annotation has been available from Java 8 to help programmers add padding to separate contended fields or classes to avoid false sharing. Originally, this annotation needs to be inserted directly into source code. When false sharing occurs where source code access is not possible, such as in class files, @Contended is not applicable.

To improve this limitation, our tool inserts the annotation into Java class files instead of source code.

Usage

To compile / execute the program, Apache Commons BCEL 6.5.0 is necessary. Other versions may also work but we have not tested.

Compile

javac -cp .:bcel-6.5.0.jar InsertContendedIntoClassFile.java

Insert the annotation for the field myField in the class file MyClass.class

java -cp .:bcel-6.5.0.jar InsertContendedIntoClassFile MyClass myField

Insert the annotation for the class MyClass itself in the class file MyClass.class

java -cp .:bcel-6.5.0.jar InsertContendedIntoClassFile MyClass

Limitations

At the moment, fields can only be specified by names. We can improve the program to let programmers specify fields by both names and descriptors, but this will require programmers to input field descriptors.

We assume that fields or classes to be annotated do not have any runtime visible annotation before insertion. Existing annotations will be overriden. This could simply be improved by adding an annotation entry for @Contended to the current annotation table, instead of overriding it.

Our tool currently only supports inserting the annotation for specific fields or classes. The usage of @Contended also allows specifying contention groups by passing the group name as a parameter to the annotation. We consider to support this use case in the near future.