package edu.washington.escience.myria.util;

import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Helper class to aid in Thread debugging.
 *
 */
public final class ThreadUtils {

  /** Prevent construction of utility class. */
  private ThreadUtils() {}

  /** The logger for this class. */
  private static final Logger LOGGER = LoggerFactory.getLogger(ThreadUtils.class);

  /**
   * @return the currently-live threads.
   */
  public static Set<Thread> getCurrentThreads() {
    return Thread.getAllStackTraces().keySet();
  }

  /**
   * Print out the list of currently active threads.
   *
   * @param tag a string printed before the message. For identifying calls to this function.
   */
  public static void printCurrentThreads(final String tag) {
    final Set<Thread> threadSet = getCurrentThreads();
    StringBuilder sb = new StringBuilder();
    sb.append(tag + ":" + threadSet.size() + " threads currently active.\n");
    sb.append('\t');
    for (final Thread t : threadSet) {
      sb.append(t.getId() + '[' + t.getName() + "], ");
    }
    sb.append('\n');
    LOGGER.warn(sb.toString());
  }

  /** Time constant. */
  private static final double NS_PER_SEC = 1e9;
  /** Lower bound on thread CPU time. */
  private static final double THREAD_CPU_LB = 0.01;

  /**
   * Prints the total CPU usage of every thread.
   */
  public static void printThreadCpuTime() {
    StringBuilder sb = new StringBuilder();
    ThreadMXBean threadMX = ManagementFactory.getThreadMXBean();
    for (Thread t : getCurrentThreads()) {
      long threadId = t.getId();
      double cpuTimeInSec = threadMX.getThreadCpuTime(threadId) / NS_PER_SEC;
      if (cpuTimeInSec > THREAD_CPU_LB) {
        sb.append('\t')
            .append(threadId)
            .append(":")
            .append(t.getName())
            .append(' ')
            .append(cpuTimeInSec)
            .append('\n');
      }
    }
    LOGGER.warn(sb.toString());
  }
}