fix code

hutool-core/src/test/java/org/dromara/hutool/core/lang/SingletonTest.java

@@ -16,9 +16,13 @@ import org.dromara.hutool.core.exception.HutoolException;
 import org.dromara.hutool.core.thread.ThreadUtil;
 import lombok.Data;
 import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import java.time.Duration;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 
 public class SingletonTest {
 
@@ -65,4 +69,21 @@ public class SingletonTest {
 	static class C{
 		private B b = Singleton.get(B.class);
 	}
+
+	@Test
+	@Disabled
+	void issue3435Test() {
+		final String key = "123";
+		final ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 10, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
+		for (int i = 0; i < 100; i++) {
+			threadPoolExecutor.execute(() -> {
+				Singleton.get(key, () -> {
+					System.out.println(key);
+					return "123";
+				});
+			});
+		}
+
+		ThreadUtil.sleep(5000);
+	}
 }

hutool-db/src/main/java/org/dromara/hutool/db/ds/DSPool.java

@@ -13,6 +13,7 @@
 package org.dromara.hutool.db.ds;
 
 import org.dromara.hutool.core.io.IoUtil;
+import org.dromara.hutool.core.lang.Singleton;
 import org.dromara.hutool.core.map.MapUtil;
 import org.dromara.hutool.core.map.SafeConcurrentHashMap;
 import org.dromara.hutool.core.spi.SpiUtil;
@@ -42,17 +43,13 @@ public class DSPool implements Closeable {
 
 	private static final String CONNECTION_PREFIX = "connection.";
 
-	private static class SingletonHolder {
-		private static final DSPool INSTANCE = new DSPool();
-	}
-
 	/**
 	 * 获取单例池对象
 	 *
 	 * @return 数据源池
 	 */
 	public static DSPool getInstance() {
-		return SingletonHolder.INSTANCE;
+		return Singleton.get(DSPool.class.getName(), DSPool::new);
 	}
 
 	/**

hutool-extra/src/main/java/org/dromara/hutool/extra/pinyin/engine/houbb/HoubbEngine.java

@@ -37,10 +37,8 @@ import com.github.houbb.pinyin.util.PinyinHelper;
  */
 public class HoubbEngine implements PinyinEngine {
 
-	/**
-	 * 汉字拼音输出的格式
-	 */
-	PinyinStyleEnum format;
+	// 汉字拼音输出的格式
+	private PinyinStyleEnum format;
 
 	/**
 	 * 构造

hutool-extra/src/main/java/org/dromara/hutool/extra/pinyin/engine/jpinyin/JPinyinEngine.java

@@ -40,18 +40,31 @@ import com.github.stuxuhai.jpinyin.PinyinHelper;
 public class JPinyinEngine implements PinyinEngine {
 
 	//设置汉子拼音输出的格式
-	PinyinFormat format;
+	private PinyinFormat format;
 
-	public JPinyinEngine(){
+	/**
+	 * 构造
+	 */
+	public JPinyinEngine() {
 		this(null);
 	}
 
-	public JPinyinEngine(final PinyinFormat format){
+	/**
+	 * 构造
+	 *
+	 * @param format {@link PinyinFormat}
+	 */
+	public JPinyinEngine(final PinyinFormat format) {
 		init(format);
 	}
 
-	public void init(PinyinFormat format){
-		if(null == format){
+	/**
+	 * 初始化格式
+	 *
+	 * @param format 格式{@link PinyinFormat}
+	 */
+	public void init(PinyinFormat format) {
+		if (null == format) {
 			// 不加声调
 			format = PinyinFormat.WITHOUT_TONE;
 		}

hutool-extra/src/main/java/org/dromara/hutool/extra/pinyin/engine/pinyin4j/Pinyin4jEngine.java

@@ -44,7 +44,7 @@ import net.sourceforge.pinyin4j.format.exception.BadHanyuPinyinOutputFormatCombi
 public class Pinyin4jEngine implements PinyinEngine {
 
 	//设置汉子拼音输出的格式
-	HanyuPinyinOutputFormat format;
+	private HanyuPinyinOutputFormat format;
 
 	/**
 	 * 构造

hutool-extra/src/main/java/org/dromara/hutool/extra/pinyin/engine/tinypinyin/TinyPinyinEngine.java

@@ -41,21 +41,22 @@ public class TinyPinyinEngine implements PinyinEngine {
 	/**
 	 * 构造
 	 */
-	public TinyPinyinEngine(){
+	public TinyPinyinEngine() {
 		this(null);
 	}
 
 	/**
 	 * 构造
+	 *
 	 * @param config 配置
 	 */
-	public TinyPinyinEngine(final Pinyin.Config config){
+	public TinyPinyinEngine(final Pinyin.Config config) {
 		Pinyin.init(config);
 	}
 
 	@Override
 	public String getPinyin(final char c) {
-		if(!Pinyin.isChinese(c)){
+		if (!Pinyin.isChinese(c)) {
 			return String.valueOf(c);
 		}
 		return Pinyin.toPinyin(c).toLowerCase();