优化ThreadUtil.safeSleep，使用System.nanoTime()

hutool-core/src/main/java/cn/hutool/core/thread/ThreadUtil.java

@@ -384,18 +384,14 @@ public class ThreadUtil {
 	public static boolean safeSleep(long millis) {
 		long done = 0;
 		long before;
-		long spendTime;
-		while (done >= 0 && done < millis) {
-			before = System.currentTimeMillis();
-			if (false == sleep(millis - done)) {
+		// done表示实际花费的时间，确保实际花费时间大于应该sleep的时间
+		while (done < millis) {
+			before = System.nanoTime();
+			if (!sleep(millis - done)) {
 				return false;
 			}
-			spendTime = System.currentTimeMillis() - before;
-			if (spendTime <= 0) {
-				// Sleep花费时间为0或者负数，说明系统时间被拨动
-				break;
-			}
-			done += spendTime;
+			// done始终为正
+			done += (System.nanoTime() - before) / 1_000_000;
 		}
 		return true;
 	}

hutool-core/src/test/java/cn/hutool/core/thread/ThreadUtilTest.java

@@ -1,5 +1,6 @@
 package cn.hutool.core.thread;
 
+import cn.hutool.core.util.RandomUtil;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -11,4 +12,13 @@ public class ThreadUtilTest {
 
 		ThreadUtil.execute(() -> Assert.assertTrue(isValid));
 	}
+
+	@Test
+	public void safeSleepTest() {
+		final long sleepMillis = RandomUtil.randomLong(1, 1000);
+		// 随机sleep时长，确保sleep时间足够
+		final long l = System.currentTimeMillis();
+		ThreadUtil.safeSleep(sleepMillis);
+		Assert.assertTrue(System.currentTimeMillis() - l >= sleepMillis);
+	}
 }