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Showing posts with the label union-find

Observability of the Java Virtual Machine

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The JVM is one of the most observable runtimes. It provides us lots of tools for troubleshooting a JVM application in production. 1. Thread observability Threads are how the JVM actually does work. When something is wrong in production, the symptom is almost always a thread: stopped, blocked, leaking etc. Thread dumps work on any JVM with no  instrumentation, no agents, no restarts. <Example project link with /threaddump endpoint>         // (1) Deadlock — two threads grab the same pair of locks in opposite order.         new Thread(() -> grab(LOCK_A, LOCK_B), "deadlock-A-then-B").start();         new Thread(() -> grab(LOCK_B, LOCK_A), "deadlock-B-then-A").start(); http://localhost:8080/actuator/threaddump To list the JVMS, we can use the command below. PS C:\observe-jvm> jps -lv 25296 jdk.jcmd/sun.tools.jps.Jps -Dapplication.home=C:\Program Files\Microsoft\jdk-21.0.3.9-hotspot -Xms8m -Djdk.module.main=...

Dynamic Connectivity Problem and the Union-Find Algorithm

Lets say we need to connect some objects and query if some objects are connected or not. Below is an example test: @Test     public void testConnectivity() {         MyConnectionDb connectDb = new MyConnectionDb();         connectDb.connect(4, 3);         connectDb.connect(3, 8);         connectDb.connect(6, 5);         connectDb.connect(9, 4);         connectDb.connect(2, 1);         assertTrue(connectDb.isConnected(8, 9));         assertFalse(connectDb.isConnected(5, 4));         connectDb.connect(5, 0);         connectDb.connect(7, 2);         connectDb.connect(6, 1);         connectDb.connect(7, 3);         assertTrue(connectDb.isConnected(5, 3));     } So whe...

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