/**
 * A program that starts several threads, each of which performs the
 * same computation.  The user specifies the number of threads.  The
 * point is to see that the threads finish in an indeterminate order.
 */
public class ThreadTest1 {
   
   
   /**
    * When a thread belonging to this class is run it will count the
    * number of primes between 2 and 1000000.  It will print the result
    * to standard output, along with its id number and the elapsed
    * time between the start and the end of the computation.
    */
   private static class CountPrimesThread extends Thread {
      int id;  // An id number for this thread; specified in the constructor.
      public CountPrimesThread(int id) {
         this.id = id;
      }
      public void run() {
         long startTime = System.currentTimeMillis();
         int count = countPrimes(2,1000000);
         long elapsedTime = System.currentTimeMillis() - startTime;
         System.out.println("Thread " + id + " counted " + 
               count + " primes in " + (elapsedTime/1000.0) + " seconds.");
      }
   }
   
   
   /**
    * Start several CountPrimesThreads.  The number of threads, between 1 and 25,
    * is specified by the user.
    */
   public static void main(String[] args) {
      int numberOfThreads = 0;
      while (numberOfThreads < 1 || numberOfThreads > 25) {
         System.out.print("How many threads do you want to use  (from 1 to 25) ?  ");
         numberOfThreads = TextIO.getlnInt();
         if (numberOfThreads < 1 || numberOfThreads > 25)
            System.out.println("Please enter a number between 1 and 25 !");
      }
      System.out.println("\nCreating " + numberOfThreads + " prime-counting threads...");
      CountPrimesThread[] worker = new CountPrimesThread[numberOfThreads];
      for (int i = 0; i < numberOfThreads; i++)
         worker[i] = new CountPrimesThread( i );
      for (int i = 0; i < numberOfThreads; i++)
         worker[i].start();
      System.out.println("Threads have been created and started.");
   }
   
   
   /**
    * Compute and return the number of prime numbers in the range
    * min to max, inclusive.
    */
   private static int countPrimes(int min, int max) {
      int count = 0;
      for (int i = min; i <= max; i++)
         if (isPrime(i))
            count++;
      return count;
   }
   
   
   /**
    * Test whether x is a prime number.  
    * x is assumed to be greater than 1.
    */
   private static boolean isPrime(int x) {
      assert x > 1;
      int top = (int)Math.sqrt(x);
      for (int i = 2; i <= top; i++)
         if ( x % i == 0 )
            return false;
      return true;
   }


} // end class ThreadTest1