parttimenerd

If any issues arise, please don't hesitate to ask.

Setup

Before diving into the code, please clone the OpenJDK JDK repository on a machine running Linux and build it according to the build instructions.

This should give you a running OpenJDK. Add it to your path and run a simple Java "Hello, World" program to confirm everything is set up correctly.

Testing

parttimenerd

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CpuCoreHog {
    public static void main(String[] args) {
        // Get the number of available processors (cores)
        int cores = Runtime.getRuntime().availableProcessors() * 5;
        System.out.println("Running on " + cores + " cores.");
        // Create a fixed thread pool with the number of available cores
        ExecutorService executorService = Executors.newFixedThreadPool(cores);

parttimenerd

import java.io.IOException;
import java.net.*;

import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpExchange;

class HttpRequestsExample {

    private static HttpServer server;

parttimenerd

Hello-eBPF

• GitHub: https://github.com/parttimenerd/hello-ebpf
• Blog: https://mostlynerdless.de/

eBPF

• main page: https://ebpf.io
• some information: https://www.brendangregg.com/ebpf.html
• https://www.infoq.com/presentations/facebook-google-bpf-linux-kernel/

parttimenerd

• segment.setUtf8String(0, obj); -> segment.setString(0, obj);
• same with getUtf8String
• MemoryLayout.sequenceLayout(JAVA_BYTE) -> MemoryLayout.sequenceLayout(0, JAVA_BYTE)
• arena.allocateUtf8String(string) -> allocateFrom(string)
• var readers = arena.allocateArray(PanamaUtil.POINTER, perfBuffers.size()); -> var readers = arena.allocate(PanamaUtil.POINTER, perfBuffers.size());
• jextract:
  • Callbacks: "X" -> "X.function"
  • bcc_symbol.module$get(sym) -> module(sym)
• Lib.open(pathInC, O_RDONLY) (var args (?)) -> Lib.open.makeInvoker().apply(pathInC, O_RDONLY) (extern int open(const char *__file, int __oflag, ...))

parttimenerd

"""
Sample file to test the trace module.

This should print:

    ...
    ********** Trace Results **********
    Used classes:
      only static init:
      not only static init:

parttimenerd

@Name("minecraft.ChunkGeneration")
@Label("Chunk Generation")
@Category({"Minecraft", "World Generation"})
class ChunkGeneration extends jdk.jfr.Event {
  @Label("Start Time")
  @Timestamp("TICKS")
  long startTime;

  @Label("Duration")
  @Timespan("TICKS")

parttimenerd

! 2023-08-01 https://twitter.com
twitter.com##a.r-13qz1uu.r-rjfia.r-1ny4l3l.r-16y2uox.r-eqz5dr.r-6koalj.r-1loqt21.r-1habvwh.css-1dbjc4n.css-18t94o4.css-4rbku5:nth-of-type(7)

! 2023-09-10 https://twitter.com
twitter.com##a.r-13qz1uu.r-oyd9sg.r-1ny4l3l.r-eqz5dr.r-13awgt0.r-6koalj.r-1loqt21.r-1habvwh.css-1dbjc4n.css-18t94o4.css-4rbku5:nth-of-type(7)

! 2023-11-21 https://twitter.com
twitter.com###id__q3p36maqo9 > div.r-13awgt0.r-1h0z5md.r-18u37iz.css-175oi2r > .r-1ny4l3l.r-lrvibr.r-bztko3.r-bt1l66.r-1777fci.css-175oi2r > .r-3s2u2q.r-clp7b1.r-o7ynqc.r-1h0z5md.r-6koalj.r-1awozwy.r-16dba41.r-rjixqe.r-a023e6.r-37j5jr.r-qvutc0.r-bcqeeo.css-1rynq56 > .r-1udh08x.r-xoduu5.css-175oi2r > span
twitter.com###id__cglm8gn7hvg > div.r-13awgt0.r-1h0z5md.r-18u37iz.css-175oi2r > .r-1ny4l3l.r-lrvibr.r-bztko3.r-bt1l66.r-1777fci.css-175oi2r > .r-3s2u2q.r-clp7b1.r-o7ynqc.r-1h0z5md.r-6koalj.r-1awozwy.r-16dba41.r-rjixqe.r-a023e6.r-37j5jr.r-qvutc0.r-bcqeeo.css-1rynq56 > .r-1udh08x.r-xoduu5.css-175oi2r > span > .r-1pn2ns4.r-1k6nrdp.r-1c

parttimenerd

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class Main {

    public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        Class<?> klass = Main.class;
        Method mainMethod = klass.getMethod("test");
        mainMethod.invoke(null);
    }

parttimenerd

public class SmallProgram {
    public static void main(String[] args) {
        String name = args[0];
        System.out.println("Hello, " + name + "!");
    }
}