Add a startup profiler for debugging

agent/agent/src/main/java/com/microsoft/applicationinsights/agent/Agent.java

@@ -42,6 +42,8 @@ public static void premain(String agentArgs, Instrumentation inst) {
     }
     OpenTelemetryAgent.premain(agentArgs, inst);
     alreadyLoaded = true;
+
+    StartupProfiler.start();
   }
 
   // this is provided only for dynamic attach in the first line of main

agent/agent/src/main/java/com/microsoft/applicationinsights/agent/StartupProfiler.java

@@ -0,0 +1,119 @@
+/*
+ * ApplicationInsights-Java
+ * Copyright (c) Microsoft Corporation
+ * All rights reserved.
+ *
+ * MIT License
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this
+ * software and associated documentation files (the ""Software""), to deal in the Software
+ * without restriction, including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software, and to permit
+ * persons to whom the Software is furnished to do so, subject to the following conditions:
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ * THE SOFTWARE IS PROVIDED *AS IS*, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+ * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+ * PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+ * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+package com.microsoft.applicationinsights.agent;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.lang.management.ManagementFactory;
+import java.lang.management.RuntimeMXBean;
+import java.lang.management.ThreadInfo;
+import java.lang.management.ThreadMXBean;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+final class StartupProfiler {
+
+  private static final String STACKTRACES = "stacktrace.txt";
+
+  public static void start() {
+    if (isReadonly()) {
+      return;
+    }
+
+    String startupProfiling = System.getProperty("-Dapplicationinsights.debug.startupProfiling");
+    if (!"true".equalsIgnoreCase(startupProfiling)) {
+      return;
+    }
+
+    String tempDirectory = System.getProperty("java.io.tmpdir");
+    File file = new File(tempDirectory, STACKTRACES);
+    try {
+      start(
+          new PrintWriter(
+              new PrintWriter(Files.newBufferedWriter(file.toPath(), Charset.defaultCharset()))));
+    } catch (IOException ignore) {
+      // ignore it for now
+    }
+  }
+
+  private static void start(PrintWriter out) {
+    Executors.newSingleThreadScheduledExecutor()
+        .scheduleAtFixedRate(new ThreadDump(out), 50, 50, TimeUnit.MILLISECONDS);
+  }
+
+  private static boolean isReadonly() {
+    File tempDir = new File(System.getProperty("java.io.tmpdir"));
+    return tempDir.canRead() && !tempDir.canWrite();
+  }
+
+  private StartupProfiler() {}
+
+  private static class ThreadDump implements Runnable {
+
+    private final PrintWriter out;
+
+    private ThreadDump(PrintWriter out) {
+      this.out = out;
+    }
+
+    @Override
+    public void run() {
+      out.println("========================================");
+      RuntimeMXBean runtimeBean = ManagementFactory.getRuntimeMXBean();
+      out.println(runtimeBean.getUptime());
+      out.println();
+      ThreadMXBean threadBean = ManagementFactory.getThreadMXBean();
+      ThreadInfo[] threadInfos =
+          threadBean.getThreadInfo(
+              threadBean.getAllThreadIds(), threadBean.isObjectMonitorUsageSupported(), false);
+      long currentThreadId = Thread.currentThread().getId();
+      for (ThreadInfo threadInfo : threadInfos) {
+        if (threadInfo.getThreadId() != currentThreadId) {
+          write(threadInfo);
+        }
+      }
+      out.flush();
+    }
+
+    private void write(ThreadInfo threadInfo) {
+      if (capture(threadInfo)) {}
+      out.println(threadInfo.getThreadName() + " #" + threadInfo.getThreadId());
+      out.println("   java.lang.Thread.State: " + threadInfo.getThreadState());
+      for (StackTraceElement ste : threadInfo.getStackTrace()) {
+        out.println("        " + ste);
+      }
+      out.println();
+    }
+
+    private static boolean capture(ThreadInfo threadInfo) {
+      if (threadInfo.getThreadName().equals("main")) {
+        return true;
+      }
+      // check stack trace length helps to skip "Signal Dispatcher" thread
+      return threadInfo.getThreadState() == Thread.State.RUNNABLE
+          && threadInfo.getStackTrace().length > 0;
+    }
+  }
+}