【Java高并发最佳实践】线程安全的单实例模式

参考资料：

高并发下线程安全的单例模式（最全最经典）

高并发Java（7）：并发设计模式 http://www.importnew.com/21312.html

1.单实例模式的线程安全的两种上佳实践：

public class SQLFactory
{
private Logger logger = LoggerFactory.getLogger(getClass());//Log.getLog(getClass());

/*//old method not thread-safe
private static SQLFactory instance = null;
public static SQLFactory getInstance() {
if (instance == null) {
instance = new SQLFactory();
}
return instance;
}
*/

//thread-safe best practice
public static SQLFactory getInstance() {
return SQLHolder.instance;
}
private static class SQLHolder {
private static SQLFactory instance = new SQLFactory();
}

/*//also good thread-safe
volatile private static SQLFactory instance = null;
public static SQLFactory getInstance() {
synchronized (SQLFactory.class) {
if (instance == null) {
instance = new SQLFactory();
}
}
return instance;
}*/
}

2.测试方法：

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import com.highgo.admin.migrator.controller.SQLFactory;

public class TestThreadSafe {
public void doing() {
System.out.println(SQLFactory.getInstance().hashCode());
}

public static void main(String[] args) {
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(4, 8, 101, TimeUnit.SECONDS,
new LinkedBlockingQueue<Runnable>(2000));

final TestThreadSafe tf = new TestThreadSafe();
for (int i = 0; i < 10; i++) {
threadPool.submit(() -> {
tf.doing();
});
}
}
}

3.测试结果：相同的实例哈希值表示始终都是同一个实例。

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