In the source code, it says that: Analysis has shown that generating the whole array allows the JIT to generate better code compared to a slimmed down array, such as one cutting off after ‘z’ So my questions are: What’s the root reason of this comment? Compared to the slimmed down array, how many performance can be improved? Answer This
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Tag: jvm
What is the use of the “dup2_x2” instruction in JVM bytecode?
Java has a dup2_x2 instruction which, according to the documentation, has the following behavior: Duplicate the top one or two values on the operand stack and insert the duplicated values, in the original order, into the operand stack. Does javac produce bytecode with this instruction? What are its potential use cases? Answer For example, the following code compiles to See,
How does java guarateee reserved memory
Checking for memory usage by stack using this command: I can see that reserved memory is different from committed. Reserved is about 1MB (default for stack). Committed in fact is physical reserved. I read that java save memory for stack while is not totally used. Running command like top I can see just committed usage. What does java/SO do in
Where is the super reference in a Java instance method’s stack frame?
I read Bill Venner’s excellent Inside the Java Virtual Machine book, which, in Chapter 5 explores in detail, among other things, the composition of a JVM’s stack frame. (This chapter from the book also happens to be officially published here: https://www.artima.com/insidejvm/ed2/jvm8.html) Apart from this book I studied relatively much the runtime data areas of some JVM’s, especially their stack and
How to fix android build error – Could not create the Java Virtual Machine
Hi I am trying to build Android apk and I get the following errors when I run the shell script. Could you suggest what I can do to resolve this please. I have latest JAVA installed Error I get is Answer You are using two JVM options that are no longer available in recent Java versions: The MaxPermSize option has
How can we know whether an object is marked as garbage by GC?
Is there any tool to visualize the status of GC on a specific object? Answer If you can access the object, it is trivially not collectable. The JVMTI system (Java Virtual Machine Tool Interface) lets other processes link up to a JVM and get stats from it. It’s what debuggers and profilers use; visualvm (ships with most JDKs) can do
What is the difference between Address and Reference in Java?
First of all, I know that Java is call by value. However, in a certain article, there is no such thing as an address in Java, and you should use the word reference. In my opinion, both words are interpreted with the same meaning. Am I wrong? What is the difference between address and reference, and do you have such
OpenJDK 8 interpreter debug
I want to see how the JVM interpreter works. Can I track function calls using NetBeans or GDB? And how will it be more convenient to do this? I’m interested in starting HelloWorld with the -Xint option and see what steps are taken and see the interpreter source code. I mean not only the result of the interpreter, but also
JVM code cache exceeds ReservedCodeCacheSize
I have a java app running in a docker with flags on OpenJDK8: -XX:+UseContainerSupport -XX:MaxRAMPercentage=80.0 -XX:NativeMemoryTracking=summary and I’ve noticed that Code Cache memory allocation …
JVM Getting the largest objects in the heap programmatically
How programmatically (from within the java application/agent) do I get a “live” summary of the largest objects in the heap (including their instances count and size)? Similarly to what Profilers do. For example, here is a screenshot from JProfiler: Usually I used to work with heap dumps in the cases where I really needed that, but now I would like
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