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@Immutable
class OneValueCache {
private final BigInteger lastNumber;
private final BigInteger[] lastFactors;
public OneValueCache(BigInteger i,
BigInteger[] factors) {
lastNumber = i;
lastFactors = Arrays.copyOf(factors, factors.length);
}
public BigInteger[] getFactors(BigInteger i) {
if (lastNumber == null || !lastNumber.equals(i))
return null;
else
return Arrays.copyOf(lastFactors, lastFactors.length);
}
}
@ThreadSafe
public class VolatileCachedFactorizer implements Servlet {
private volatile OneValueCache cache =
new OneValueCache(null, null);//这里是安全发布
public void service(ServletRequest req, ServletResponse resp) {
BigInteger i = extractFromRequest(req);
BigInteger[] factors = cache.getFactors(i);
if (factors == null) {
factors = factor(i);
//由于cache为volatile,所以最新值立即能让其它线程可见
cache = new OneValueCache(i, factors);
}
encodeIntoResponse(resp, factors);
}
}