java多线程创建与信息共享

摘要

• volatile线程工作副本的可见性
• synchronized:关键步骤加锁

线程的创建

继承Thread

public class Thread1 extends Thread{
	public void run()
	{
		System.out.println("hello");
	}
	public static void main(String[] a)
	{
		new Thread1().start();
	}
}

实现Runable

public class Thread2 implements Runnable{
	public void run()
	{
		System.out.println("hello");
	}
	public static void main(String[] a)
	{
		new Thread(new Thread2()).start();
	}
}

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java多线程信息共享

通过共享变量在多个线程中共享消息

• static变量
• 同一个Runnable类的成员变量

public class ThreadDemo0
{
	public static void main(String [] args)
	{
		new TestThread0().start();
		new TestThread0().start();
		new TestThread0().start();
		new TestThread0().start();
	}
}
class TestThread0 extends Thread  
{
	//private int tickets=100;           //每个线程卖100张，没有共享
	private static int tickets=100;  //static变量是共享的，所有的线程共享
	public void run()
	{
		while(true)
		{
			if(tickets>0)
			{
				System.out.println(Thread.currentThread().getName() +
				" is selling ticket " + tickets);
				tickets = tickets - 1;
			}
			else
			{
				break;
			}
		}
	}
}

public class ThreadDemo1
{
	public static void main(String [] args)
	{
		TestThread1 t=new TestThread1();
		new Thread(t).start();
		new Thread(t).start();
		new Thread(t).start();
		new Thread(t).start();
	}
}
class TestThread1 implements Runnable
{
	private int tickets=100;
	public void run()
	{
		while(true)
		{
			if(tickets>0)
			{
				try {
					Thread.sleep(100);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				tickets--;
				System.out.println(Thread.currentThread().getName() +" is selling ticket " + tickets);
			}
			else
			{
				break;
			}
				
		}
	}
}

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volatile 让所有线程及时看到变量值的变化

public class ThreadDemo2
{
	public static void main(String args[]) throws Exception 
	{
		TestThread2 t = new TestThread2();
		t.start();
		Thread.sleep(2000);
		t.flag = false;
		System.out.println("main thread is exiting");
	}
}

class TestThread2 extends Thread
{
	// boolean flag = true;   //子线程不会停止
	volatile boolean flag = true;  //用volatile修饰的变量可以及时在各线程里面通知
	public void run() 
	{
		int i=0;
		while(flag) // t.flag = false; 工作缓存的flag是true 需要加入volatile
		{
			i++;			
		}
		System.out.println("test thread3 is exiting");
	}	
} 

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public class ThreadDemo3 {
	public static void main(String[] args) {
		TestThread3 t = new TestThread3();
		new Thread(t, "Thread-0").start();
		new Thread(t, "Thread-1").start();
		new Thread(t, "Thread-2").start();
		new Thread(t, "Thread-3").start();
	}
}

class TestThread3 implements Runnable {
	private volatile int tickets = 100; // 多个 线程在共享的
	String str = new String("");

	public void run() {
		while (true) {
			sale();
			try {
				Thread.sleep(100);
			} catch (Exception e) {
				System.out.println(e.getMessage());
			}
			if (tickets <= 0) {
				break;
			}
		}

	}

	public synchronized void sale() { // 同步函数
		if (tickets > 0) {
			System.out.println(Thread.currentThread().getName() + " is saling ticket " + tickets--);
		}
	}
}

参考

• https://www.jianshu.com/p/35878d4ec130
• https://blog.csdn.net/weixin_39747568/article/details/112872830

问题

• tomcat在配置时设置最大线程数，当前线程数超过这个数值时会出错，那么有没有办法捕获到这个错误，从而在client端显示出错信息？