From a3eca85e12db8b5a2d80f1511b6923c27f376463 Mon Sep 17 00:00:00 2001
From: jptx1234 <jptx1234@163.com>
Date: Sun, 17 May 2020 23:29:43 +0800
Subject: [PATCH] =?UTF-8?q?Snowflake=20=E5=BE=AA=E7=8E=AF=E7=AD=89?=
 =?UTF-8?q?=E5=BE=85=E4=B8=8B=E4=B8=80=E4=B8=AA=E6=97=B6=E9=97=B4=E6=97=B6?=
 =?UTF-8?q?=E5=8A=A0=E5=85=A5=E5=AF=B9=E6=97=B6=E9=92=9F=E5=80=92=E9=80=80?=
 =?UTF-8?q?=E7=9A=84=E5=88=A4=E6=96=AD?=
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Snowflake 在循环等待下一个时间时，判断时间未发生变化的方式由<=改为==，避免了时钟突然倒退导致的长时间循环，同时加入时钟倒退检测，避免生成重复ID
---
 .../src/main/java/cn/hutool/core/lang/Snowflake.java      | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/hutool-core/src/main/java/cn/hutool/core/lang/Snowflake.java b/hutool-core/src/main/java/cn/hutool/core/lang/Snowflake.java
index b39ddb3bd..44908d7d0 100644
--- a/hutool-core/src/main/java/cn/hutool/core/lang/Snowflake.java
+++ b/hutool-core/src/main/java/cn/hutool/core/lang/Snowflake.java
@@ -177,9 +177,15 @@ public class Snowflake implements Serializable {
 	 */
 	private long tilNextMillis(long lastTimestamp) {
 		long timestamp = genTime();
-		while (timestamp <= lastTimestamp) {
+		// 循环直到操作系统时间戳变化
+		while (timestamp == lastTimestamp) {
 			timestamp = genTime();
 		}
+		if (timestamp < lastTimestamp) {
+			// 如果发现新的时间戳比上次记录的时间戳数值小，说明操作系统时间发生了倒退，报错
+			throw new IllegalStateException(
+					StrUtil.format("Clock moved backwards. Refusing to generate id for {}ms", lastTimestamp - timestamp));
+		}
 		return timestamp;
 	}