public class Main { public static void agentmain(String agentArgs) { premain(agentArgs); } public static void premain(String agentArgs) { Main main = new Main(); main.run(new Options(agentArgs)); } private void run(Options options) { Thread t = new Thread(new Profiler(options)); t.setDaemon(true); t.setName("Profiler"); t.start(); }}

欢迎大家来到IT世界,在知识的湖畔探索吧!

欢迎大家来到IT世界,在知识的湖畔探索吧!java -javaagent:./target/tiny_profiler.jar=agentArgs …

public class Options { /** interval option */ private Duration interval = Duration.ofMillis(10); /** flamegraph option */ private Optional<Path> flamePath; /** table option */ private boolean printMethodTable = true; ...}

欢迎大家来到IT世界,在知识的湖畔探索吧!Thread t = new Thread(new Profiler(options));

t.setDaemon(true);

t.setName("Profiler");t.start();

public class Profiler implements Runnable { private final Options options; private final Store store; public Profiler(Options options) { this.options = options; this.store = new Store(options.getFlamePath()); Runtime.getRuntime().addShutdownHook(new Thread(this::onEnd)); } private static void sleep(Duration duration) { // ... } @Override public void run() { while (true) { Duration start = Duration.ofNanos(System.nanoTime()); sample(); Duration duration = Duration.ofNanos(System.nanoTime()) .minus(start); Duration sleep = options.getInterval().minus(duration); sleep(sleep); } } private void sample() { Thread.getAllStackTraces().forEach( (thread, stackTraceElements) -> { if (!thread.isDaemon()) {  // exclude daemon threads store.addSample(stackTraceElements); } }); } private void onEnd() { if (options.printMethodTable()) { store.printMethodTable(); } store.storeFlameGraphIfNeeded(); }

Runtime.getRuntime().addShutdownHook(new Thread(this::onEnd));

while (true) { Duration start = Duration.ofNanos(System.nanoTime()); sample(); Duration duration = Duration.ofNanos(System.nanoTime()) .minus(start); Duration sleep = options.getInterval().minus(duration); sleep(sleep);}

Thread.getAllStackTraces().forEach( (thread, stackTraceElements) -> { if (!thread.isDaemon()) {  // exclude daemon threads store.addSample(stackTraceElements); }});

package me.bechberger;import java.io.BufferedOutputStream;import java.io.OutputStream;import java.io.PrintStream;import java.nio.file.Path;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.Optional;import java.util.stream.Stream;/** * store of the traces */public class Store { /** too large and browsers can't display it anymore */ private final int MAX_FLAMEGRAPH_DEPTH = 100; private static class Node { // ... } private final Optional<Path> flamePath; private final Map<String, Long> methodOnTopSampleCount =  new HashMap<>(); private final Map<String, Long> methodSampleCount =  new HashMap<>(); private long totalSampleCount = 0; /** * trace tree node, only populated if flamePath is present */ private final Node rootNode = new Node("root"); public Store(Optional<Path> flamePath) { this.flamePath = flamePath; } private String flattenStackTraceElement( StackTraceElement stackTraceElement) { // call intern to safe some memory return (stackTraceElement.getClassName() + "." +  stackTraceElement.getMethodName()).intern(); } private void updateMethodTables(String method, boolean onTop) { methodSampleCount.put(method,  methodSampleCount.getOrDefault(method, 0L) + 1); if (onTop) { methodOnTopSampleCount.put(method,  methodOnTopSampleCount.getOrDefault(method, 0L) + 1); } } private void updateMethodTables(List<String> trace) { for (int i = 0; i < trace.size(); i++) { String method = trace.get(i); updateMethodTables(method, i == 0); } } public void addSample(StackTraceElement[] stackTraceElements) { List<String> trace =  Stream.of(stackTraceElements) .map(this::flattenStackTraceElement) .toList(); updateMethodTables(trace); if (flamePath.isPresent()) { rootNode.addTrace(trace); } totalSampleCount++; } // the only reason this requires Java 17 :P private record MethodTableEntry( String method,  long sampleCount,  long onTopSampleCount) { } private void printMethodTable(PrintStream s,  List<MethodTableEntry> sortedEntries) { // ... } public void printMethodTable() { // sort methods by sample count // the print a table // ... } public void storeFlameGraphIfNeeded() { // ... }}

private static class Node {  private final String method;  private final Map<String, Node> children = new HashMap<>();  private long samples = 0;   public Node(String method) {  this.method = method;  }   private Node getChild(String method) {  return children.computeIfAbsent(method, Node::new);  }   private void addTrace(List<String> trace, int end) {  samples++;  if (end > 0) {  getChild(trace.get(end)).addTrace(trace, end - 1);  }  }   public void addTrace(List<String> trace) {  addTrace(trace, trace.size() - 1);  }   /**  * Write in d3-flamegraph format  */  private void writeAsJson(PrintStream s, int maxDepth) {  s.printf("{ \"name\": \"%s\", \"value\": %d, \"children\": [",  method, samples);  if (maxDepth > 1) {  for (Node child : children.values()) {  child.writeAsJson(s, maxDepth - 1);  s.print(",");  }  }  s.print("]}");  }   public void writeAsHTML(PrintStream s, int maxDepth) {  s.print("""  <head>  <link rel="stylesheet"  type="text/css"  href="https://cdn.jsdelivr.net/npm/d3-flame-graph@4.1.3/dist/d3-flamegraph.css">  </head>  <body>  <div id="chart"></div>  <script type="text/javascript"  src="https://d3js.org/d3.v7.js"></script>  <script type="text/javascript"  src="https://cdn.jsdelivr.net/npm/d3-flame-graph@4.1.3/dist/d3-flamegraph.min.js"></script>  <script type="text/javascript">  var chart = flamegraph().width(window.innerWidth);  d3.select("#chart").datum(""");  writeAsJson(s, maxDepth);  s.print("""  ).call(chart);  window.onresize =  () => chart.width(window.innerWidth);  </script>  </body>  """);  }

# build itmvn package
# run your program and print the table of methods sorted by their sample count# and the flame graph, taking a sample every 10msjava -javaagent:target/tiny-profiler.jar=flamegraph=flame.html ...
你可以在renaissance dotty基准测试上运行，并创建如前所示的火焰图：
# download a benchmark> test -e renaissance.jar || wget https://github.com/renaissance-benchmarks/renaissance/releases/download/v0.14.2/renaissance-gpl-0.14.2.jar -O renaissance.jar> java -javaagent:./target/tiny_profiler.jar=flamegraph=flame.html -jar renaissance.jar dotty...===== method table ======Total samples: 11217Method Samples Percentage On top Percentagedotty.tools.dotc.typer.Typer.typed 59499 530.44 2 0.02dotty.tools.dotc.typer.Typer.typedUnadapted 31050 276.81 7 0.06scala.runtime.function.JProcedure1.apply 24283 216.48 13 0.12dotty.tools.dotc.Driver.process 19012 169.49 0 0.00dotty.tools.dotc.typer.Typer.typedUnnamed$1 18774 167.37 7 0.06dotty.tools.dotc.typer.Typer.typedExpr 18072 161.11 0 0.00scala.collection.immutable.List.foreach 16271 145.06 3 0.03...