线程与进程

什么是JUC

java.until工具包、包、分类

线程和进程

进程：一个程序。QQ.exe等等程序的集合

一个进程往往包含多个进程，至少包含一个

Java默认包含几个线程？2个 main GC

Java可以开启线程吗

public synchronized void start() {
    /**
     * This method is not invoked for the main method thread or "system"
     * group threads created/set up by the VM. Any new functionality added
     * to this method in the future may have to also be added to the VM.
     *
     * A zero status value corresponds to state "NEW".
     */
    if (threadStatus != 0)
        throw new IllegalThreadStateException();

    /* Notify the group that this thread is about to be started
     * so that it can be added to the group's list of threads
     * and the group's unstarted count can be decremented. */
    group.add(this);

    boolean started = false;
    try {
        start0();
        started = true;
    } finally {
        try {
            if (!started) {
                group.threadStartFailed(this);
            }
        } catch (Throwable ignore) {
            /* do nothing. If start0 threw a Throwable then
              it will be passed up the call stack */
        }
    }
}

private native void start0();

调用本地方法，底层的C++，Java无法直接操作硬件

并发，并行

并发编程：并发、并行

并发(多线程操作同一个资源)

CPU一核，模拟出来多条线程，天下武功，唯快不破，快速交替并行(多个人一起行走)
CPU多核，多个线程可以同时执行;线程池

package com.cz.demo1;

/**
 * @author 卓亦苇
 * @version 1.0
 * 2023/2/28 16:38
 */
public class Test {
    public static void main(String[] args) {
        //获取cpu核数
        System.out.println(Runtime.getRuntime().availableProcessors());
    }
}

并发编程的本质:充分利用CPU的资源

所有的公司都很看重!

企业，挣钱=>提高效率，裁员，找一个厉害的人顶替三个不怎么样的人;

人员(减)、技术成本（高)

线程的状态

public enum State {
    //线程新生
    NEW,

    //运行
    RUNNABLE,
    //阻塞
    BLOCKED,

    //等待
    WAITING,

    //超时等待
    TIMED_WAITING,

    //终止
    TERMINATED;
}

wait/sleep

来自不同的类

wait => Object
sleep => Thread
关于锁的释放
wait 会释放锁，sleep睡觉了，抱着锁睡觉，不会释放！
使用范围不同
wait：必须在同步代码块
sleep可以再任何地方睡
是否需要捕获异常
wait 不需要捕获异常
sleep必须要捕获异常

Lock

传统Synchoronized

Lock锁

package com.cz.demo1;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @author 卓亦苇
 * @version 1.0
 * 2023/2/28 22:54
 */
public class TestLock2 {
    public static void main(String[] args) {
        Ticket2 ticket2 = new Ticket2();

        new Thread(()->{for (int i = 0; i < 40; i++) {ticket2.sale();}},"A").start();
        new Thread(()->{for (int i = 0; i < 40; i++) {ticket2.sale();}},"B").start();
        new Thread(()->{for (int i = 0; i < 40; i++) {ticket2.sale();}},"C").start();

    }
}
//资源类 OOP
class Ticket2{
    //属性、方法
    private int num = 30;
    Lock lock = new ReentrantLock();
    //买票方式
    public void sale(){
        lock.lock();//加锁
        try {
            if(num>0){
                System.out.println(Thread.currentThread().getName()+"卖出了" +
                        num--+"票，剩余"+num);
            }
        }finally {
            lock.unlock();//解锁
        }
    }

}