/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */
package org.apache.hive.http;

import java.io.IOException;
import java.io.PrintStream;
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * A servlet to print out the current stack traces.
 */
public class StackServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
  private static ThreadMXBean threadBean =
      ManagementFactory.getThreadMXBean();

  @Override
  public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    if (!HttpServer.isInstrumentationAccessAllowed(getServletContext(),
        request, response)) {
      return;
    }
    response.setContentType("text/plain; charset=UTF-8");
    try (PrintStream out = new PrintStream(
        response.getOutputStream(), false, "UTF-8")) {
      printThreadInfo(out, "");
    }
  }

  /**
   * Print all of the thread's information and stack traces.
   *
   * @param stream the stream to
   * @param title a string title for the stack trace
   */
  private synchronized void printThreadInfo(
      PrintStream stream, String title) {
    final int STACK_DEPTH = 20;
    boolean contention = threadBean.isThreadContentionMonitoringEnabled();
    long[] threadIds = threadBean.getAllThreadIds();
    stream.println("Process Thread Dump: " + title);
    stream.println(threadIds.length + " active threads");
    for (long tid : threadIds) {
      ThreadInfo info = threadBean.getThreadInfo(tid, STACK_DEPTH);
      if (info == null) {
        stream.println("  Inactive");
        continue;
      }
      stream.println("Thread " +
          getTaskName(info.getThreadId(), info.getThreadName()) + ":");
      Thread.State state = info.getThreadState();
      stream.println("  State: " + state);
      stream.println("  Blocked count: " + info.getBlockedCount());
      stream.println("  Wtaited count: " + info.getWaitedCount());
      if (contention) {
        stream.println("  Blocked time: " + info.getBlockedTime());
        stream.println("  Waited time: " + info.getWaitedTime());
      }
      if (state == Thread.State.WAITING) {
        stream.println("  Waiting on " + info.getLockName());
      } else if (state == Thread.State.BLOCKED) {
        stream.println("  Blocked on " + info.getLockName());
        stream.println("  Blocked by " +
            getTaskName(info.getLockOwnerId(), info.getLockOwnerName()));
      }
      stream.println("  Stack:");
      for (StackTraceElement frame : info.getStackTrace()) {
        stream.println("    " + frame.toString());
      }
    }
    stream.flush();
  }

  private String getTaskName(long id, String name) {
    if (name == null) {
      return Long.toString(id);
    }
    return id + " (" + name + ")";
  }
}