Java 关于线程的一些使用

╰+哭是因爲堅強的太久メ 2022-05-21 23:49 188阅读 0赞

public class Demo {
    
        public static void main(String[] agr) throws Exception {
            Demo demo = new Demo();
            demo.test();
        }
    
    
        //线程的wait,notify必须和synchronized一起使用
        //即,当前线程拿属于object的锁之后,就可以调用wait让此线程进入等待状态,然后抛出锁,等待其他线程那到object的锁之后唤醒
        //挂在object上的线程,如果有多个线程挂在object一个对象上那么notify只会唤醒一个线程
        public Object object = new Object();
    
        public void test() throws InterruptedException {
    
            new Thread() {
                @Override
                public void run() {
                    synchronized (object) {
                        L.d("线程1进入等待状态");
                        try {
                            object.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        L.d("线程1继续运行");
                    }
                }
            }.start();
    
            new Thread() {
                @Override
                public void run() {
                    synchronized (object) {
                        L.d("线程2进入等待状态");
                        try {
                            object.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        L.d("线程2继续运行");
                    }
                }
            }.start();
            new Thread() {
                @Override
                public void run() {
                    synchronized (object) {
                        L.d("线程3进入等待状态");
                        try {
                            object.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        L.d("线程3继续运行");
                    }
                }
            }.start();
    
            Thread.sleep(1000);
            synchronized (object) {
                object.notify();
            }
        }
    
    }

如果像下面这个没有拿到锁就调起wait就会抛出IllegalMonitorStateException异常

new Thread() {
                @Override
                public void run() {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }.start();

或者是这样,虽然拿到了object的锁但是并没有挂起在object这个对象上就也会抛出异常

new Thread() {
                @Override
                public void run() {
                    synchronized (object){
                        try {
                            wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
    
                }
            }.start();

上面两种直接调用的wait是将自己直接挂在Thread本类这个对象上所以要进行拿到本类对象的锁才可以,像下面这样就不会抛出异常

public void test() throws InterruptedException {
            Thread thread = new Thread() {
                @Override
                public synchronized void run() {
                    L.d("线程开始");
                    try {
                        wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    L.d("线程完成等待");
                }
            };
    
            thread.start();
    
            Thread.sleep(1000);
            synchronized (thread) {
                thread.notify();
            }
        }

有关线程的状态

<table> 
 <tbody> 
  <tr> 
   <td>NEW</td> 
   <td>刚刚创建的线程尚且没有运行</td> 
  </tr> 
  <tr> 
   <td>RUNNABLE</td> 
   <td>正在运行中的线程</td> 
  </tr> 
  <tr> 
   <td>WAITING</td> 
   <td>线程等待中</td> 
  </tr> 
  <tr> 
   <td>TIMED_WAITING</td> 
   <td>计时等待,调用wait(long timeout)之后所处的状态</td> 
  </tr> 
  <tr> 
   <td>BLOCKED</td> 
   <td>阻塞状态,synchronized的锁已经被其他线程拿到而没有释放,此时线程被阻塞在synchronized</td> 
  </tr> 
  <tr> 
   <td>TERMINATED</td> 
   <td>终止状态,线程运行完成</td> 
  </tr> 
 </tbody> 
</table>

> 另外如果线程调用sleep是不会释放已经拿到的synchronized锁,如果是调用wait方法则会释放已经到的synchronized锁
> 
> 关于thread.join()方法的使用,如果在a线程中调用了b线程的join方法,那么a线程就会进入等待直至b线程执行完成才会继续执行,用网上的专业一点的说法就是将线程由并行转为串行,join内部调用的就是wait方法,

例子：

public void test() {
            Thread thread1 = new Thread() {
                @Override
                public void run() {
                    for (int i = 0; i < 10; i++) {
    
                        try {
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        L.d("线程1 : " + i);
                    }
                }
            };
            thread1.start();
    
            Thread thread2 = new Thread() {
                @Override
                public void run() {
                    for (int i = 0; i < 10; i++) {
                        try {
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        L.d("线程2 : " + i);
                        try {
                            if (i == 5) {
                                thread1.join();
                            }
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            };
            thread2.start();
        }

join方法的源码:

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;
                }
            }
        }