このテスト スレッド コードから抜粋したこのコードでは、スレッドが 2 つのメソッドaddToTotal()を呼び出しますcountPrimes()が、前者のみが同期とマークされています。
が実行されているときにインターリーブを防止するものcountPrimes()。countPrimes()i、min、max、count などで使用される変数も共有リソースではありませんか。そして、isPrime()によって呼び出されるのは何countPrimes()ですか？
public class ThreadTest2 {
private static final int START = 3000000;
private static int total;
synchronized private static void addToTotal(int x) {
total = total + x;
System.out.println(total + " primes found so far.");
}
private static class CountPrimesThread extends Thread {
int count = 0;
int min, max;
public CountPrimesThread(int min, int max) {
this.min = min;
this.max = max;
}
public void run() {
count = countPrimes(min,max);
System.out.println("There are " + count +
" primes between " + min + " and " + max);
addToTotal(count);
}
}
private static void countPrimesWithThreads(int numberOfThreads) {
int increment = START/numberOfThreads;
System.out.println("\nCounting primes between " + (START+1) + " and "
+ (2*START) + " using " + numberOfThreads + " threads...\n");
long startTime = System.currentTimeMillis();
CountPrimesThread[] worker = new CountPrimesThread[numberOfThreads];
for (int i = 0; i < numberOfThreads; i++)
worker[i] = new CountPrimesThread(START+i*increment+1, START+(i+1)*increment );
total = 0;
for (int i = 0; i < numberOfThreads; i++)
worker[i].start();
for (int i = 0; i < numberOfThreads; i++) {
while (worker[i].isAlive()) {
try {
worker[i].join();
} catch (InterruptedException e) {
}
}
}
long elapsedTime = System.currentTimeMillis() - startTime;
System.out.println("\nThe number of primes is " + total + ".");
System.out.println("\nTotal elapsed time: " + (elapsedTime/1000.0) + " seconds.\n");
}
public static void main(String[] args) {
int processors = Runtime.getRuntime().availableProcessors();
if (processors == 1)
System.out.println("Your computer has only 1 available processor.\n");
else
System.out.println("Your computer has " + processors + " available processors.\n");
int numberOfThreads = 0;
while (numberOfThreads < 1 || numberOfThreads > 5) {
System.out.print("How many threads do you want to use (from 1 to 5) ? ");
numberOfThreads = TextIO.getlnInt();
if (numberOfThreads < 1 || numberOfThreads > 5)
System.out.println("Please enter 1, 2, 3, 4, or 5 !");
}
countPrimesWithThreads(numberOfThreads);
}
private static int countPrimes(int min, int max) {
int count = 0;
for (int i = min; i <= max; i++)
if (isPrime(i))
count++;
return count;
}
private static boolean isPrime(int x) {
int top = (int)Math.sqrt(x);
for (int i = 2; i <= top; i++)
if ( x % i == 0 )
return false;
return true;
}
}