Automatic Object Inlining in a Java Virtual Machine

Object-oriented Java applications allocate many small objects linked together by field references. Object inlining tries to reduce the number of objects and therefore the number of pointer indirections by merging the referenced object with the referencing one. In programming languages like C++ and C#, this merging can be performed by the programmer with explicit value objects, but Java does not offer this possibility in favor of a simpler object model. Automatic object inlining transforms reference objects to value objects when it can be proven that the semantics are not affected. This provides the access speed of value objects without complicating the object model. Typical examples that can be optimized by object inlining are collections: The highly reusable collection classes can be automatically embedded into the users' data objects, eliminating the reference from the data object to the collection object. We develop an extension of the Java HotSpot Virtual Machine so that inlinable objects are detected and optimized at run time.