Thread详解
Java并发之AQS详解
Thread中join实现如下：
public final synchronized void join(long millis) throws InterruptedException { long base = System.currentTimeMillis(); long now = 0; if (millis < 0) { throw new IllegalArgumentException("timeout value is negative"); } if (millis == 0) { while (isAlive()) { wait(0); } } else { while (isAlive()) { long delay = millis - now; if (delay <= 0) { break; } wait(delay); now = System.currentTimeMillis() - base; } }}其中利用了Object的wait方法，调用的前提是已经获得join线程的锁，如果thread对象被锁住则会等待其被释放。
import core.AbstractCommonConsumer;import core.CommonUtils;import core.MagnetMonitor;import core.NamedThreadPoolExecutor;import org.apache.ibatis.io.Resources;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.lang.reflect.InvocationTargetException;import java.util.Date;import java.util.LinkedList;import java.util.List;import java.util.concurrent.*;import java.util.concurrent.locks.LockSupport;class JoinTester01 implements Runnable { private String name; JoinTester01(String name) { this.name = name; } public void run() { System.out.printf("%s begins: %s\n", name, new Date()); try { TimeUnit.SECONDS.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } System.out.printf("%s has finished: %s\n", name, new Date()); }}class JoinTester02 implements Runnable { Thread thread; JoinTester02(Thread thread) { this.thread = thread; } Thread getThread(){ return this.thread; } public void run() { synchronized (thread) { System.out.printf("getObjectLock at %s\n", new Date()); try { Thread.sleep(2000); } catch (InterruptedException ex) { ex.printStackTrace(); } System.out.printf("ReleaseObjectLock at %s\n", new Date()); } try { Thread.sleep(1000); } catch (InterruptedException ex) { ex.printStackTrace(); } synchronized (thread) { System.out.printf("getObjectLock again at %s\n", new Date()); try { Thread.sleep(2000); } catch (InterruptedException ex) { ex.printStackTrace(); } System.out.printf("ReleaseObjectLock again at %s\n", new Date()); } }}class TestMain { public static void main(String[] args) { Thread thread = new Thread(new JoinTester01("Leon")); JoinTester02 tester02 = new JoinTester02(thread); Thread getLockThread = new Thread(tester02); getLockThread.start(); thread.start(); try { System.out.printf("start join at %s\n", new Date()); thread.join(1000); System.out.printf("stop join at %s\n", new Date()); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } }}start join at Sun Jun 30 18:40:08 CST 2019Leon begins: Sun Jun 30 18:40:08 CST 2019getObjectLock at Sun Jun 30 18:40:08 CST 2019ReleaseObjectLock at Sun Jun 30 18:40:10 CST 2019stop join at Sun Jun 30 18:40:11 CST 2019getObjectLock again at Sun Jun 30 18:40:11 CST 2019ReleaseObjectLock again at Sun Jun 30 18:40:13 CST 2019Leon has finished: Sun Jun 30 18:40:18 CST 2019