I believe there are free tools to do it, but even making your own tool is easy. JVMTI will help. Here is a simple JVMTI agent I made to trace all exceptions: #include <jni.h> #include <jvmti.h> #include <string.h> #include <stdio.h> void JNICALL ExceptionCallback(jvmtiEnv* jvmti, JNIEnv* env, jthread thread, jmethodID method, jlocation location, jobject exception, jmethodID … Read more
Unfortunately PrintGCApplicationStoppedTime is misleading name for this JVM option. In fact it prints the time spent inside safepoints. Safepoint pauses occur not only due to Garbage Collection, but for many other reasons: Deoptimization Biased lock revocation Thread dump Heap inspection Class redifinition etc. (see the list) Safepoints may happen periodically even without a requested VM … Read more
⚠️ For JetBrains IntelliJ IDEA: Go to Help -> Edit Custom Properties…. Create the file if it asks you to create it. To disable the error message paste the following to the file you created: idea_rt idea.no.launcher=true This will take effect on the restart of the IntelliJ.
Theory There are two possible exceptions: OutOfMemoryError: Java heap space means your array does not fit into java heap space. In order to solve you can increase the maximum heap size by using JVM option -Xmx. Also take into account that the maximum size of object cannot be larger than the largest heap generation. OutOfMemoryError: … Read more
HotSpot compilation policy is rather complex, especially for Tiered Compilation, which is on by default in Java 8. It’s neither a number of executions, nor a matter of CompileThreshold parameter. The best explanation (apparently, the only reasonable explanation) can be found in HotSpot sources, see advancedThresholdPolicy.hpp. I’ll summarize the main points of this advanced compilation … Read more
jmap vs. jmap -F, as well as jstack vs. jstack -F use completely different mechanisms to communcate with the target JVM. jmap / jstack When run without -F these tools use Dynamic Attach Mechanism. This works as follows. Before connecting to Java process 1234, jmap creates a file .attach_pid1234 at the working directory of the … Read more
This is really linked to HotSpot and the default option values (Java HotSpot VM Options) which differ between client and server configuration. From Chapter 2 of the whitepaper (The Java HotSpot Performance Engine Architecture): The JDK includes two flavors of the VM — a client-side offering, and a VM tuned for server applications. These two … Read more
Tips about writing micro benchmarks from the creators of Java HotSpot: Rule 0: Read a reputable paper on JVMs and micro-benchmarking. A good one is Brian Goetz, 2005. Do not expect too much from micro-benchmarks; they measure only a limited range of JVM performance characteristics. Rule 1: Always include a warmup phase which runs your … Read more