A multi‐granularity locking scheme for java packedobjects based on a concurrent multiway tree

Abstract

SummaryIn this paper, we develop a multi‐granularity locking scheme for Java PackedObjects, an experimental enhancement introduced in IBM's J9 Java Virtual Machine. The packed object model organizes data in a multi‐tier manner in which object data can be nested in the container object instead of being pointed to by an object reference, as in the traditional Java object model. This new object data model creates new challenges for multi‐tier data synchronization, requiring concurrent locks on the multi‐tier data of different granularities for maintaining consistency. This is different from the traditional Java synchronization model. In this paper we make use of a concurrent multiway tree to represent the containing and ordering relationship between PackedObjects at different tiers and develop an efficient multi‐granularity locking scheme allowing multiple threads to concurrently manipulate the concurrent multiway tree for synchronization operations. In the evaluation, we compare our new tree‐based multitierSync with the previous multitierSync approaches based on linked‐lists (optimized‐list‐based and lazy‐list‐based). The experimental results show that the tree‐based MultitierPackedSync outperforms the list‐based approaches considerably in different workloads, and the higher the workload, the better the performance gains achieved by the tree‐based MultitierPackedSync.