JUC并发编程

什么是JUC

java.util 工具包，包，分类

业务：普通的线程代码：Thread

Runnable 没有返回值，效率相对Callable较低

线程和进程

线程、进程，如果不能用一句话说出来的技术，不扎实！

进程：一个程序，QQ.exe、Music.exe程序的集合

一个进程往往可以包含多个线程，至少有一个

java默认有两个线程，main线程和GC进程

java真的能开启线程吗 开不了

  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 */
             }
         }
     }
 //本地方法，底层的C++，Java无法直接操作硬件
     private native void start0();

并发、并行

并发编程;并发，并行

并发（多个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；

package com.Study;
 ​
 import org.omg.SendingContext.RunTime;
 ​
 public class demo01 {
     public static void main(String[] args) {
         //获取CPU的核数
         //CPU密集型，IO密集型
         System.out.println(Runtime.getRuntime().availableProcessors());
     }
 }