Observability of the Java Virtual Machine

-
Image
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=...
Post a Comment

More fun with left shift operator

-
Lets say we want to have sum of two integers. But we are not allowed to use + and - operators. Below is a way to do that:

 public class Solution {

    public static int getSum(int a, int b) {

        if (a > 0 && b > 0) {
            return positiveSum(a, b);
        }

        if (a < 0 && b < 0) {
            return negate(positiveSum(Math.abs(a), Math.abs(b)));
        }

        if (a > 0 && b < 0) {
            return minus(a, Math.abs(b));
        } else {
            return minus(b, Math.abs(a));
        }
    }

    private static int minus(int a, int b) {
        boolean[] result = new boolean[32];

        boolean carry = false;

        for (int i = 0; i < 32; ++i) {

            boolean ba = ((a & (1 << i))) != 0;
            boolean bb = (b & (1 << i)) != 0;

            result[i] = ba ^ bb;

            if (carry) {
                result[i] = !result[i];
            }

            if (ba == true) {
                carry = false;
            }

            if (ba == false && bb == true) {
                carry = true;
            }

        }

        int intResult = getIntResult(result);

        return intResult;


    }

    private static int positiveSum(int a, int b) {
        boolean[] result = new boolean[32];

        boolean carry = false;

        for (int i = 0; i < 32; ++i) {

            boolean ba = ((a & (1 << i))) != 0;
            boolean bb = (b & (1 << i)) != 0;

            result[i] = ba ^ bb ^ carry;

            if (carry == true) {
                if (result[i] == true) {
                    carry = false;
                }
            }

            if ((a & (1 << i)) != 0) {
                if ((b & (1 << i)) != 0) {
                    carry = true;
                }
            }
        }

        int intResult = getIntResult(result);

        return intResult;
    }

    private static int getIntResult(boolean[] result) {
        int intResult = 0;
        for (int i = 0; i < result.length; ++i) {

            if (result[i] == true)
                intResult |= (1 << i);

        }
        return intResult;
    }
    // negate a positive value
    private static int negate(int value) {
        if (value < 0) {
            throw new RuntimeException();
        }

        return minus(0, value);
    }
 
    public static void main(String[] args) {

        System.out.println(getSum(-17, -10));
        System.out.println(getSum(17, -10));
        System.out.println(getSum(-10, 17));
        System.out.println(getSum(-15, 32));
        System.out.println(getSum(15, 32));
    }
}

Comments

Post a Comment

Popular posts from this blog

The WeakReference class, monitoring memory leak and garbage collection in a Java application

-
Image
 Below is a Stack implementation that uses an internal resizeable array structure.  public class MyStack< T > implements Stack< T > { private static final int CAPACITY = 100 ; private Object[] array ; private int pos = 0 ; public MyStack () { this . array = new Object[ CAPACITY ] ; } @Override public void push ( T item) { if ( pos >= array . length / 2 ) { Object[] newArray = new Object[ pos * 2 ] ; System. arraycopy ( array , 0 , newArray , 0 , array . length ) ; array = newArray ; } array [ pos ++] = item ; } @Override public T pop () { if (isEmpty()) { throw new RuntimeException( "empty stack" ) ; } @SuppressWarnings ( "unchecked" ) T item = ( T ) array [ pos - 1 ] ; pos -= 1 ; return item ; } @Override @SuppressWarnings ( "unchecked" ) public T peek...
Read more

Simplescalar Simulator - Part 2: sim-outorder.c

-
sim-outorder implements a very detailed out-of-order issue superscalar processor with a two-level memory system and speculative execution support. This simulator is a performance simulator, tracking the latency of all pipeline operations. Let's have a look at SimpleScalar simulator's code related to iTLB. (Instruction Translation Lookaside Buffer) First, there are simulator options related to iTLB: /* register simulator-specific options */ void sim_reg_options(struct opt_odb_t *odb) { /* TLB options */ opt_reg_string(odb, "-tlb:itlb", "instruction TLB config, i.e., { |none}", &itlb_opt, "itlb:16:4096:4:l", /* print */TRUE, NULL); opt_reg_int(odb, "-tlb:lat", "inst/data TLB miss latency (in cycles)", &tlb_miss_lat, /* default */30, /* print */TRUE, /* format */NULL); } /* check simulator-specific option values */ void  sim_check_options(... ) { /* sim-outorder.c  line: 1098*/   /* u...
Read more

Notes on Java Performance

-
Performance monitoring, performance profiling and performance tuning are different activities. For example, monitoring is not an intrusive action but profiling is. Because it may be changing the responsiveness of the running application. User CPU utilization vs Kernel CPU utilization: The ideal situation is when Kernel CPU utilization is 0%. So ideally, all the CPU cycles must be spent on our application code. JVM just in time compiler performs dynamic optimizations. So it makes decisions while the program is running and generates native code with better performance. Java 1.0 was completely interpreted but beginning with Java 1.1.8, there was a just-in-time compiler. It was 8 times faster. After that, paralellizing the garbage collector was a huge improvement. There are hundreds of Java tuning flags. https://github.com/ScottOaks/JavaPerformanceTuning Boolean flags use this syntax: -XX:+FlagName enables the flag, and -XX:-FlagName disables the flag. 32 BIT VS 64 BIT Fr...
Read more