For example, the HotSpot JVM implement null-pointer detection by catching SIGSEGV signal. So if we manually generate a SIGSEGV from external, will that also be recognized as NullPointerException in...

Can someone explain the differences between GraalVM and Jvm-Hotspot, and how GraalVM is related to OpenJDK's HotSpot.

I am working on a Java application for solving a class of numerical optimization problems - large-scale linear programming problems to be more precise. A single problem can be split up into smaller...

Prior to Java 8 we had 5 major runtime data areas: Method Area Heap JVM Stacks PC registers Native method stacks With Java 8, there is no Perm Gen, that means there is no more “java.lang.Out...

I have a hard time understanding how compressed pointers works in Java 19, help is appreciated. In Java 11 the reference size is 4 for heaps below 32GiB (compressed pointers) and 8 for a larger hea...

We're using Wildfly 11 with Java 8 on Amazon Linux. We recently installed jstack to troubleshoot a high CPU utilization issue as we're trying to figure out what code is causing the CPU to spin. Fir...

I keep fighting to understand what VarHandle::setOpaque and VarHandle::getOpaque are really doing. It has not been easy so far - there are some things I think I get (but will not present them in th...

Question How to get a rolling recording into disk, with a maximum age? Context When something goes bad in my server, I want to be able to dump the profiling information of the hours prior and analy...

I have a java code which looks like this: private volatile boolean myWriteActionPending; void startWrite() { boolean prev = myWriteActionPending; myWriteActionPending = true; try { // acquire w...

We run a complex clustered application with Java 11.0.11 and -XX:ReservedCodeCacheSize=375m with the same load profile attached 24/7 without any restarts. After we updated AdoptOpenJDK jdk-11.0.11+...

In one of my computers, there is JRE 1.8.0_45 and in another machine there is OpenJDK. I want to set the JVM flag Dlog4j2.formatMsgNoLookups=true, but where can I write this piece of configuration?...

Looking into UTF8 decoding performance, I noticed the performance of protobuf's UnsafeProcessor::decodeUtf8 is better than String(byte[] bytes, int offset, int length, Charset charset) for the foll...

I had to run jmap in order to take heap dump of my process. but jvm returned: Unable to open socket file: target process not responding or HotSpot VM not loaded The -F option can be used when the ...

I just read the Java Magazine article Loop Unrolling. There the authors demonstrate that simple for loops with an int counter are compiled with loop unrolling optimization: private long intStride1(...

Suppose I have a java.util.Collection that I want to loop over. Normally I'd do this: for(Thing thing : things) do_something_with(thing); But suppose that this is in some core utility method that ...

I need to do some experiments showing the effect of inlining on my code. Anybody knows how to disable inlining with sun jvm? I searched http://www.oracle.com/technetwork/java/javase/tech/vmoptions-...

Consider the following function: int foo(int[] indices) { int[] lookup = new int[256]; fill(lookup); // populate values, not shown int sum = 0; for (int i : indices) { sum += lookup[i & 0...

In the "Effective Java", the author mentioned that while (!done) i++; can be optimized by HotSpot into if (!done) { while (true) i++; } I am very confused about it. The variable done is us...

As suggested in this answer, I am using the following flags when running performance tests. -XX:+PrintCompilation -verbose:gc This was very useful for debugging what JVM activities were happenin...

I just want to control the stack size for all of my threads in a Java (groovy) application. For the Hotspot Oracle VM, I know that there are two parameters doing that (-Xss and XX:ThreadStackSize)....

I was analyzing the HotSpot logs for a benchmark I ran for a piece of code in JITWatch and noticed a lot of methods calls not being inlined due to "no static binding". These seem to only ...

In reading about ZGC I notice that it brags about being a 'single-generation garbage collector,' but I rarely see any details on exactly what this term means. Normal Generational GC I'm familiar wi...

I want to monitor Full GC frequency in JMX. A MBean exposes GC count. (cf. http://download.oracle.com/javase/1.5.0/docs/api/java/lang/management/GarbageCollectorMXBean.html - java.lang:type=Garbage...

Tried looking up for this, but all the questions/answers I came across talk about the purpose of having 2 survivor spaces. I would like to understand the purpose of having survivor space in general...

Is an instance variable of an object in Java stored on the stack or method area of the JVM? Also, do we have different instance variable for multiple threads? If it is stored in method area how ...