10/11/2023 0 Comments Netbeans jdk 12Concurrent Marking (longer concurrent phase).Initial Marking (short stop the world phase, traces the root set).Two of these are short stop the world phases, and the other 2 are longer phases that can run concurrently with Java threads: This extra word is only added when the Shenendoah GC is in use. This allows the object to be moved without updating all references to it, meaning live objects can be updated while Java threads are running concurrently. All references to the object have to go through this pointer. Shenendoah adds a third word called an Indirection Pointer. Normally OpenJDK object headers have 2 words allocated to them (the class name and a mark word used for locking, forward pointers etc). It can do evacuation work and compact the heap while Java threads are running, reducing pause times even further. The pause time is independent of the heap size (a large heap would have the same pause time as a smaller heap). However it also uses concurrent evacuation, which G1 does not. Like G1, Shenendoah can work alongside the application threads. You can read much more detail about G1GC here. This algorithm provides shorter pause times. Unlike Parallel GC, it only uses ‘stop the world’ when doing a full garbage collection. Since Java 9, the default GC has been Garbage First (G1). It used multiple threads for GC, but froze all other application threads while doing so (an approach known as ‘stop the world’ which led to high pause times). In Java 8, the default GC was the Parallel Garbage Collector, which prioritized high throughput. It is not designed to be the best for every scenario, but if you want responsiveness and a GC that takes advantage of modern machines with more memory and more processors, it is an interesting option. It requires more space than other algorithms. The trade off is that it prioritises responsiveness over throughput and memory footprint. The purpose is to provide good responsiveness and short, reliable pause times. Shenendoah is a concurrent and parallel open source Garbage Collector. The default Garbage Collector in Java 12 will still be G1, but it also comes with a new experimental GC called Shenendoah. Garbage collection has always been one of the killer features of Java over other languages such as C, and there are big changes here. While Java 12 is not a long-term release, it does see some very significant enhancements. In this article, we look at the new Garbage collection options. In other articles, we looked at Java 12’s JVM Constants API explained in 5 minutes, Java 12 made microbenchmarking easier and Java 12 Switch Expressions explained in 5 minutes This month we are focusing on Java 12 new features you should know about. She has spoken at conferences including JavaOne/Code One, DevFest and NetBeans days. Bethan Palmer Bethan is a Java developer and a Java Champion.
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