CyclicBarrier のサンプル。

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class Solver {
  public static void main(String args) {
    float matrix = new float[10][10];
    for (int i = 0; i < matrix.length; i++) {
      for (int j = 0; j < matrix[i].length; j++) {
        matrix[i][j] = (i + 1) * (j + 1);
      }
    }

    new Solver(matrix);
  }

  final int N;

  final float data;

  final CyclicBarrier barrier;

  class Worker implements Runnable {
    int myRow;
    boolean done;

    Worker(int row) {
      myRow = row;
    }

    public void run() {
      while (!done()) {
        System.out.println("processRow(" + myRow+ ") : " + Thread.currentThread());

        try {
          barrier.await();
        } catch (InterruptedException ex) {
          return;
        } catch (BrokenBarrierException ex) {
          return;
        }
        done = true;
      }
    }

    private boolean done() {
      return done;
    }
  }

  public Solver(float[] matrix) {
    data = matrix;
    N = matrix.length;
    barrier = new CyclicBarrier(N, new Runnable() {
      public void run() {
        System.out.println("mergeRows() : " + Thread.currentThread());
      }
    });
    for (int i = 0; i < N; ++i)
      new Thread(new Worker(i)).start();

    System.out.println("waitUntilDone() : " + Thread.currentThread());
    System.exit(0);
  }
}