Towards an Efficient Pauseless Java GC with Selective HTM-Based Access Barriers

Abstract

The garbage collector (GC) is a critical component of any managed runtime environment (MRE), such as the Java virtual machine. While the main goal of the GC is to simplify and automate memory management, it may have a negative impact on the application performance, especially on multi-core systems. This is typically due to stop-the-world pauses, i.e., intervals for which the application threads are blocked during the collection. Existing approaches to concurrent GCs allow the application threads to perform at the same time as the GC at the expense of throughput and simplicity. In this paper we build upon an existing pauseless transactional GC algorithm and design an important optimization that would significantly increase its throughput. More precisely, we devise selective access barriers, that define multiple paths based on the state of the garbage collector. Preliminary evaluation of the selective barriers shows up to 93% improvement over the initial transactional barriers in the worst case scenario. We estimate the performance of a pauseless GC having selective transactional barriers and find it to be on par with Java's concurrent collector.