java多线程中的join()、 sleep()、 yield()、 wait()函数

join()

当线程t1调用t2.join()后，t1保持锁对象，等待t2执行完，t1进入可执行状态；

package thread;

public class JoinRunnable implements Runnable {
	
	Thread t1 ,t2;
	
	public JoinRunnable() {
		t1 = new Thread(this);
		t1.setName("t1");
		t2 = new Thread(this);
		t2.setName("t2");
	}

	@Override
	public void  run() { //如果加上synchronized锁标记，那么即使t1线程调用了t2.join()；由于join不释放锁，t2还是无法按预期执行
             System.out.println(Thread.currentThread().getName()); 
             
             if(Thread.currentThread()==t1){	////////
            	 try {
            		System.out.println("t2.join();");
					t2.join();	/////////////////
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
             }
             
             for (int i = 0; i < 10; i++) {
            	 System.out.println(Thread.currentThread().getName()); 
			}
	}

	public static void main(String[] args){
		JoinRunnable runnable = new JoinRunnable();
		runnable.t1.start();
		runnable.t2.start();
	}
	
}

运行结果：

t1
t2
t2.join();
t2
t2
t2
t2
t2
t2
t2
t2
t2
t2
t1
t1
t1
t1
t1
t1
t1
t1
t1
t1

----------------------------------------------------------------------------------------------------------------------------

sleep()

在线程t1中调用sleep(time),t1保持锁对象，进入阻塞状态，time完成后，t1进入可执行状态。给了低优先级线程执行的机会。

package thread;

public class SleepRunnable implements Runnable {
	
	@Override
	public synchronized void  run() {
		 for(int i=0; i<3; i++){ 
             System.out.println(Thread.currentThread().getName()+":"+i); 
             try{ 
                 Thread.sleep(100);	//线程调用了sleep(100)，由于sleep不释放锁，其它线程依然无法进入run函数
             } 
             catch(InterruptedException e){ 
                 System.out.println("Interrupted"); 
             } 
         } 
	}

	public static void main(String[] args){
		SleepRunnable myrun = new SleepRunnable();
		Thread t1 = new Thread(myrun);
		t1.setName("t1");
		Thread t2 = new Thread(myrun);
		t2.setName("t2");
		t1.start();
		t2.start();
	}
	
}

运行结果：

t1:0
t1:1
t1:2
t2:0
t2:1
t2:2

----------------------------------------------------------------------------------------------------------------------------

yield()

当线程调用yield()，线程直接进入可执行状态，不放锁

package thread;

public class YieldRunnable implements Runnable {
	
	@Override
	public void  run() { //这里如果用synchronized标记，则其它线程无法进入
		 for(int i=0; i<3; i++){ 
             System.out.println(Thread.currentThread().getName()+":"+i); 
             Thread.yield();<span style="white-space:pre">		</span>//////////////
         } 
	}

	public static void main(String[] args){
		YieldRunnable myrun = new YieldRunnable();
		Thread t1 = new Thread(myrun);
		t1.setName("t1");
		Thread t2 = new Thread(myrun);
		t2.setName("t2");
		t1.start();
		t2.start();
	}
	
}

运行结果:

t1:0
t2:0
t1:1
t2:1
t1:2
t2:2

----------------------------------------------------------------------------------------------------------------------------

wait()

当现在t1在调用wait()后，线程释放拥有的锁，进入线程等待池。当其他线程调用notify时，JVM从线程等待池中取走某一线程，放入锁标志等待池。

package thread;

public class WaitRunnable implements Runnable {
	
	Thread t1 ,t2;
	
	public WaitRunnable() {
		t1 = new Thread(this);
		t1.setName("t1");
		t2 = new Thread(this);
		t2.setName("t2");
	}

	@Override
	public synchronized void  run() {
             if(Thread.currentThread()==t1){
            		System.out.println("----------"+Thread.currentThread().getName()+" wait 10");
					try {
						wait(10);<span style="white-space:pre">		</span>////////////
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
             }
             for (int i = 0; i < 10; i++) {
            	 System.out.println(Thread.currentThread().getName()); 
			}
             if(Thread.currentThread()==t2){
            	 System.out.println("---------- t2 done");
            	 notifyAll();<span style="white-space:pre">		</span>////////////
             }else{
            	 System.out.println("---------- t1 done");
             }
	}

	public static void main(String[] args){
		WaitRunnable runnable = new WaitRunnable();
		runnable.t1.start();
		runnable.t2.start();
	}
	
}

运行结果：

----------t1 wait 10
t2
t2
t2
t2
t2
t2
t2
t2
t2
t2
---------- t2 done
t1
t1
t1
t1
t1
t1
t1
t1
t1
t1
---------- t1 done