问如何锁定和同步更新primes[]和total？

EN

public class PrimeBuggy implements Runnable {
//private static int start, N;
//I changed above line to following:
private final int start,N;
private static int numThreads;
private static int primes[];
private static boolean pflag[];
private static int total = 0;
//I created a lock
private Lock lock();
this.start = start;
this.N = N;
private static boolean is_prime(int v) {
    int i;
    int bound = (int)Math.floor(Math.sqrt((double)v)) + 1;
    for (i = 2; i < bound; i++) {
        if (pflag[i])
            continue;
        if (v % i == 0) {
            pflag[v] = true;
            return false;
        }
    }
    return (v > 1);
}    

/***/
private int threadNum;
private PrimeBuggy(int threadNum) { this.threadNum = threadNum; }
public void run() {
    int i;
    //lock this begining
    lock.lock();
    start = N/numThreads * threadNum;
    N = start + N/numThreads;
    for (i = start; i < N; i++) {
        if (is_prime(i)) {
            primes[total] = i;
            total++;
            //unlock at the end
            lock.unlock();
        }
    }
}