Android Application doing too much work on its main thread error. Pls help.

package com.example.sarvesh007.othello;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.os.SystemClock;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import java.sql.Time;
import java.util.Timer;

@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public class GameActivity extends AppCompatActivity implements View.OnClickListener{

    Button squares[][]= new Button[8][8];
    int matrix[][] = new int[8][8];
    int col = 0, row = 0;
    String TAG = GameActivity.class.getSimpleName();
    Drawable userButtonIcon, computerButtonIcon, emptyButtonIcon;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_game);
        userButtonIcon = findViewById(R.id.button).getBackground();
        computerButtonIcon =findViewById(R.id.button4).getBackground();
        emptyButtonIcon = findViewById(R.id.button2).getBackground();
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                startBoard();
            }
        });


    }



    @Override
    public void onClick(final View v) {
        {
            int k = 0, matri[][] = new int[8][8];

            for (int i = 0; i < 8; i++) {
                for (int j = 0; j < 8; j++) {
                    if (v.getId() == squares[i][j].getId()) {
                        k++;
                        col = i;      //Possible logical error check values of col and row
                        row = j;      //Possible logical error check values of col and row
                        break;
                    }

                }
                if (k > 0)
                    break;
            }

            if (matrix[col][row] != 2 && matrix[col][row] != 1)
                matrix[col][row] = 1; // Possible logical error check values of col and row

                 for (int i = 0; i < 8; i++) {
                   for (int j = 0; j < 8; j++) {
                     matri[i][j] = matrix[i][j];
               }
            }
            new Thread(new Runnable() {
                @Override
                public void run() {
                    matrix = Processor.Move(matrix, row, col);
                }
            }).start();

            setBoard(matrix);
            new Thread(new Runnable() {
                @Override
                public void run() {
                    matrix = Processor.computerMove(matrix);
                }
            }).start();

            setBoard(matrix);

            int temp = 0;
            for (int i = 0; i < 8; i++) {
                for (int j = 0; j < 8; j++) {
                    if (matri[i][j] != matrix[i][j])
                        temp++;
                }
            }
            if (temp == 0) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getBaseContext(), "Illegal Move!", Toast.LENGTH_LONG).show();
                    }
                });
            }


        }
    }

        public void setBoard ( int[][] matrix){
            for (int i = 0; i < 8; i++)
                for (int j = 0; j < 8; j++)
                    switch (matrix[i][j]) {
                        case 1:
                            squares[i][j].setBackground(userButtonIcon);
                            break;
                        case 2:
                            squares[i][j].setBackground(computerButtonIcon);
                            break;
                        default:
                            squares[i][j].setBackground(emptyButtonIcon);
                            break;
                    }
            Log.i(TAG, "Board set");
            SystemClock.sleep(1000);
        }


        private void startBoard () {

            squares[0][0] = findViewById(R.id.square1x1);
            squares[0][1] = findViewById(R.id.square1x2);
            squares[0][2] = findViewById(R.id.square1x3);
            squares[0][3] = findViewById(R.id.square1x4);
            squares[0][4] = findViewById(R.id.square1x5);
            squares[0][5] = findViewById(R.id.square1x6);
            squares[0][6] = findViewById(R.id.square1x7);
            squares[0][7] = findViewById(R.id.square1x8);

            squares[1][0] = findViewById(R.id.square2x1);
            squares[1][1] = findViewById(R.id.square2x2);
            squares[1][2] = findViewById(R.id.square2x3);
            squares[1][3] = findViewById(R.id.square2x4);
            squares[1][4] = findViewById(R.id.square2x5);
            squares[1][5] = findViewById(R.id.square2x6);
            squares[1][6] = findViewById(R.id.square2x7);
            squares[1][7] = findViewById(R.id.square2x8);

            squares[2][0] = findViewById(R.id.square3x1);
            squares[2][1] = findViewById(R.id.square3x2);
            squares[2][2] = findViewById(R.id.square3x3);
            squares[2][3] = findViewById(R.id.square3x4);
            squares[2][4] = findViewById(R.id.square3x5);
            squares[2][5] = findViewById(R.id.square3x6);
            squares[2][6] = findViewById(R.id.square3x7);
            squares[2][7] = findViewById(R.id.square3x8);

            squares[3][0] = findViewById(R.id.square4x1);
            squares[3][1] = findViewById(R.id.square4x2);
            squares[3][2] = findViewById(R.id.square4x3);
            squares[3][3] = findViewById(R.id.square4x4);
            squares[3][4] = findViewById(R.id.square4x5);
            squares[3][5] = findViewById(R.id.square4x6);
            squares[3][6] = findViewById(R.id.square4x7);
            squares[3][7] = findViewById(R.id.square4x8);

            squares[4][0] = findViewById(R.id.square5x1);
            squares[4][1] = findViewById(R.id.square5x2);
            squares[4][2] = findViewById(R.id.square5x3);
            squares[4][3] = findViewById(R.id.square5x4);
            squares[4][4] = findViewById(R.id.square5x5);
            squares[4][5] = findViewById(R.id.square5x6);
            squares[4][6] = findViewById(R.id.square5x7);
            squares[4][7] = findViewById(R.id.square5x8);

            squares[5][0] = findViewById(R.id.square6x1);
            squares[5][1] = findViewById(R.id.square6x2);
            squares[5][2] = findViewById(R.id.square6x3);
            squares[5][3] = findViewById(R.id.square6x4);
            squares[5][4] = findViewById(R.id.square6x5);
            squares[5][5] = findViewById(R.id.square6x6);
            squares[5][6] = findViewById(R.id.square6x7);
            squares[5][7] = findViewById(R.id.square6x8);

            squares[6][0] = findViewById(R.id.square7x1);
            squares[6][1] = findViewById(R.id.square7x2);
            squares[6][2] = findViewById(R.id.square7x3);
            squares[6][3] = findViewById(R.id.square7x4);
            squares[6][4] = findViewById(R.id.square7x5);
            squares[6][5] = findViewById(R.id.square7x6);
            squares[6][6] = findViewById(R.id.square7x7);
            squares[6][7] = findViewById(R.id.square7x8);

            squares[7][0] = findViewById(R.id.square8x1);
            squares[7][1] = findViewById(R.id.square8x2);
            squares[7][2] = findViewById(R.id.square8x3);
            squares[7][3] = findViewById(R.id.square8x4);
            squares[7][4] = findViewById(R.id.square8x5);
            squares[7][5] = findViewById(R.id.square8x6);
            squares[7][6] = findViewById(R.id.square8x7);
            squares[7][7] = findViewById(R.id.square8x8);

            for (int i = 0; i < 8; i++)
                for (int j = 0; j < 8; j++) {
                    squares[i][j].setOnClickListener(this);
                    squares[i][j].setBackground(findViewById(R.id.button2).getBackground());
                    Log.i(TAG, "OnCLickListener set");
                }
            squares[3][3].setBackground(userButtonIcon);
            squares[3][4].setBackground(computerButtonIcon);
            squares[4][3].setBackground(computerButtonIcon);
            squares[4][4].setBackground(userButtonIcon);

            matrix[3][3] = 1;
            matrix[4][3] = 2;
            matrix[3][4] = 2;
            matrix[4][4] = 1;


        }

    }