线程唯一的单例

经典设计模式的单例模式是指进程唯一的对象实例，实现code如下：

package cun.zheng.weng.design.sinstnce;import java.util.concurrent.CountDownLatch;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;public class IdGenerator {private IdGenerator(){}private AtomicLong generator = new AtomicLong(0);static class IdGeneratorHolder {private final static IdGenerator ID_GENERATOR = new IdGenerator();}public static IdGenerator getInstance(){return IdGeneratorHolder.ID_GENERATOR;}public Long getId(){return generator.getAndIncrement();}public static void main(String[] args) throws InterruptedException {ThreadPoolExecutor executor = new ThreadPoolExecutor(3,3,1000, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<>());CountDownLatch latch = new CountDownLatch(10);for(int i=0;i<10;i++){Integer taskId = i;executor.submit(()->{Long threadId = Thread.currentThread().getId();System.out.println("Task "+ taskId +" generate id->" + IdGenerator.getInstance().getId() + " ,task done by "+ threadId);latch.countDown();});}latch.await();executor.shutdownNow();}
}输出结果：
Task 0 generate id->0 ,task done by 9
Task 1 generate id->1 ,task done by 10
Task 2 generate id->2 ,task done by 11
Task 3 generate id->3 ,task done by 9
Task 5 generate id->5 ,task done by 10
Task 4 generate id->4 ,task done by 11
Task 7 generate id->7 ,task done by 10
Task 6 generate id->6 ,task done by 9
Task 9 generate id->9 ,task done by 10
Task 8 generate id->8 ,task done by 11

别跟我扯什么双重检测单例模式，性能太差，不考虑，单例模式就用静态内部类实现，高性能+延迟加载，还要什么双重检测！

那么，问题来了，如果我要实现线程绑定呢，换句话说就是实现线程间唯一的单例，进程中可以有多个实例。

思路很简单：将线程id绑定对象实例就行了。以下使用Map和JDK原生的ThreadLocal实现这个想法。

package cun.zheng.weng.design.sinstnce;import java.util.Map;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicLong;public class ThreadSingleInstance {private ThreadSingleInstance(){}AtomicLong atomicLong = new AtomicLong(0);private static final Map<Long,ThreadSingleInstance> idGeneratorHolder = new ConcurrentHashMap<>();public Long getId(){return atomicLong.getAndIncrement();}public static ThreadSingleInstance getInstance(){Long threadId = Thread.currentThread().getId();idGeneratorHolder.putIfAbsent(threadId,new ThreadSingleInstance());return idGeneratorHolder.get(threadId);}public static void main(String[] args) throws InterruptedException {ThreadPoolExecutor executor = new ThreadPoolExecutor(3,3,1000, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<>());CountDownLatch latch = new CountDownLatch(10);for(int i=0;i<10;i++){Integer taskId = i;executor.submit(()->{Long threadId = Thread.currentThread().getId();System.out.println("Task "+ taskId +" generate id->" + ThreadSingleInstance.getInstance().getId() + " ,task done by "+ threadId);latch.countDown();});}latch.await();executor.shutdownNow();}
}输出：
Task 1 generate id->0 ,task done by 10
Task 2 generate id->0 ,task done by 11
Task 3 generate id->1 ,task done by 10
Task 4 generate id->1 ,task done by 11
Task 5 generate id->2 ,task done by 10
Task 6 generate id->2 ,task done by 11
Task 7 generate id->3 ,task done by 10
Task 8 generate id->3 ,task done by 11
Task 9 generate id->4 ,task done by 10
Task 0 generate id->0 ,task done by 9

package cun.zheng.weng.design.sinstnce;import java.util.concurrent.CountDownLatch;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;public class ThreadInstanceByThreadLocal {private ThreadInstanceByThreadLocal(AtomicLong atomicLong){this.atomicLong = atomicLong;}private AtomicLong atomicLong;public Long getId(){return atomicLong.getAndIncrement();}public static ThreadInstanceByThreadLocal getInstance(){return new ThreadInstanceByThreadLocal(new AtomicLong(0));}public static void main(String[] args) throws InterruptedException {ThreadPoolExecutor executor = new ThreadPoolExecutor(3,3,1000, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<>());CountDownLatch latch = new CountDownLatch(10);ThreadLocal<ThreadInstanceByThreadLocal> threadLocal = new ThreadLocal<ThreadInstanceByThreadLocal>(){@Overrideprotected ThreadInstanceByThreadLocal initialValue() {return ThreadInstanceByThreadLocal.getInstance();}};for(int i=0;i<10;i++){Integer taskId = i;executor.submit(()->{Long threadId = Thread.currentThread().getId();System.out.println("Task "+ taskId +" generate id->" + threadLocal.get().getId() + " ,task done by "+ threadId);latch.countDown();});}latch.await();executor.shutdownNow();}
}