content: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  import java.lang.reflect.Field;
  import java.util.Map;
  
  public class Main implements Runnable {
      static final int numberOfThreads = 5;
      static final int totalOperations = 1000;
  
      public static void main(String[] args) throws Exception {
          final Thread[] threads = new Thread[numberOfThreads];
          for (int t = 0; t < threads.length; t++) {
              threads[t] = new Thread(new Main());
              threads[t].start();
          }
          for (Thread t : threads) {
              t.join();
          }
          // Do this test after the other part to leave some time for the heap task daemon to start
          // up.
          test_getStackTraces();
          System.out.println("Finishing");
      }
  
      static Thread getHeapTaskDaemon() throws Exception {
          Field f = ThreadGroup.class.getDeclaredField("systemThreadGroup");
          f.setAccessible(true);
          ThreadGroup systemThreadGroup = (ThreadGroup) f.get(null);
  
          while (true) {
              int activeCount = systemThreadGroup.activeCount();
              Thread[] array = new Thread[activeCount];
              systemThreadGroup.enumerate(array);
              for (Thread thread : array) {
                 if (thread.getName().equals("HeapTaskDaemon") &&
                     thread.getState() != Thread.State.NEW) {
                    return thread;
                  }
              }
              // Yield to eventually get the daemon started.
              Thread.sleep(10);
          }
      }
  
      static void test_getStackTraces() throws Exception {
          Thread heapDaemon = getHeapTaskDaemon();
  
          // Force a GC to ensure the daemon truly started.
          Runtime.getRuntime().gc();
          // Check all the current threads for positive IDs.
          Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();
          for (Map.Entry<Thread, StackTraceElement[]> pair : map.entrySet()) {
              Thread thread = pair.getKey();
              // Expect empty stack trace since we do not support suspending the GC thread for
              // obtaining stack traces. See b/28261069.
              if (thread == heapDaemon) {
                  System.out.println(thread.getName() + " depth " + pair.getValue().length); 
              }
          }
      }
  
      public void test_getId() {
          if (Thread.currentThread().getId() <= 0) {
              System.out.println("current thread's ID is not positive");
          }
          // Check all the current threads for positive IDs.
          Map<Thread, StackTraceElement[]> stMap = Thread.getAllStackTraces();
          for (Thread thread : stMap.keySet()) {
              if (thread.getId() <= 0) {
                  System.out.println("thread's ID is not positive: " + thread.getName());
              }
          }
      }
  
      public void run() {
          for (int i = 0; i < totalOperations; ++i) {
              test_getId();
          }
      }
  }
  