package umontreal.iro.lecuyer.util;

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

/**
 * Extends the {@link AbstractChrono} 
 * class to compute the CPU time for a single thread. It is available
 * only under Java 1.5 which provides platform-independent 
 * facilities to get the CPU time for a single thread through management API.
 * 
 * 

 * Note that this chrono might not work properly on some systems running Linux because
 * of a bug in Sun's implementation or Linux kernel.
 * For instance, this class unexpectedly computes the global CPU time
 * under Fedora 
 * Core 4, kernel 2.6.17 and JRE version 1.5.0-09.
 * With Fedora Core 6, kernel 2.6.20, the function is working properly.
 * As a result, one should not rely on this bug to get the global CPU time.
 * 
 * 

 * Note that the above bug does not prevent one from using this chrono to
 * compute the CPU time for a single-threaded application.  In that case,
 * the global CPU time corresponds to the CPU time of the current thread.
 * 
 * 

 * Running timer fonctions when the associated thread is dead will return 0.
 * 
 */
public class ThreadCPUTimeChrono extends AbstractChrono {
   private  long           myThreadId;
   static   ThreadMXBean   threadMXBean = null;

   protected void getTime (long[] tab) {
      long rawTime = getTime();
      final long DIV = 1000000000L;
      long seconds = rawTime/DIV;
      long micros = (rawTime % DIV)/1000L;
      tab[0] = seconds;
      tab[1] = micros;
   }

   protected long getTime() {
      if (threadMXBean == null) {
         // We use lazy initialization to avoid a potential exception being wrapped into a confusing
         // ExceptionInInitializerError. That would happen if this initialization was in a static block instead of
         // in this method.
         threadMXBean = ManagementFactory.getThreadMXBean();
         if (!threadMXBean.isThreadCpuTimeEnabled())
            // Call this only when necessary, because this can throw a SecurityException if
            // run under a security manager.
            threadMXBean.setThreadCpuTimeEnabled (true);
      }
      long time = threadMXBean.getThreadCpuTime(myThreadId);
      return time < 0 ? 0 : time;
   }


   /**
    * Constructs a ThreadCPUTimeChrono object associated 
    *   with current thread and initializes it to zero.
    * 
    */
   public ThreadCPUTimeChrono() {
      super();
      myThreadId = Thread.currentThread().getId();
      init();
   }


   /**
    * Constructs a ThreadCPUTimeChrono object associated 
    *   with the given {@link Thread} variable and initializes it to zero.
    * 
    */
   public ThreadCPUTimeChrono(Thread inThread) {
      super();
      myThreadId = inThread.getId();
      init();
   }


}