JUC概述

JUC概述1：

首先是进程和线程的概念：

进程：是指系统在系统中正在运行的一个应用程序，程序一旦运行就是进程，进程是资源分配的最小单位

线程：进程之内独立执行，是程序执行的最小单位

线程的六大状态：在线程的枚举类中

 public enum State {         /**          * Thread state for a thread which has not yet started.          */         NEW,          /**          * Thread state for a runnable thread.  A thread in the runnable          * state is executing in the Java virtual machine but it may          * be waiting for other resources from the operating system          * such as processor.          */         RUNNABLE,          /**          * Thread state for a thread blocked waiting for a monitor lock.          * A thread in the blocked state is waiting for a monitor lock          * to enter a synchronized block/method or          * reenter a synchronized block/method after calling          * {@link Object#wait() Object.wait}.          */         BLOCKED,          /**          * Thread state for a waiting thread.          * A thread is in the waiting state due to calling one of the          * following methods:          * <ul>          *   <li>{@link Object#wait() Object.wait} with no timeout</li>          *   <li>{@link #join() Thread.join} with no timeout</li>          *   <li>{@link LockSupport#park() LockSupport.park}</li>          * </ul>          *          * <p>A thread in the waiting state is waiting for another thread to          * perform a particular action.          *          * For example, a thread that has called {@code Object.wait()}          * on an object is waiting for another thread to call          * {@code Object.notify()} or {@code Object.notifyAll()} on          * that object. A thread that has called {@code Thread.join()}          * is waiting for a specified thread to terminate.          */         WAITING,          /**          * Thread state for a waiting thread with a specified waiting time.          * A thread is in the timed waiting state due to calling one of          * the following methods with a specified positive waiting time:          * <ul>          *   <li>{@link #sleep Thread.sleep}</li>          *   <li>{@link Object#wait(long) Object.wait} with timeout</li>          *   <li>{@link #join(long) Thread.join} with timeout</li>          *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>          *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>          * </ul>          */         TIMED_WAITING,          /**          * Thread state for a terminated thread.          * The thread has completed execution.          */         TERMINATED;     }

状态名称说明new初始状态runnable运行状态blocked阻塞状态waiting等待状态，一直等(不见不散)time_waiting超时等待，（过时不候）terminated终止状态

wait和sleep的区别：

sleep是Thread的静态方法，wait是Object的方法，任何对象实例化都能调用
sleep不会释放锁，他也不需要占用锁，wait会释放锁，但是调用它的前提是当前线程占有锁
它们都可以interrupted被中断

并发和并行：

并发是指多个事情在同一个时间段中执行

并行是指多个事情在同一时刻执行

管程：

是一种同步机制，保证同一时间内只有一个线程访问被保护数据或者代码

jvm同步基于进入(加锁)和退出(解锁)，是管程对象实现的

大意就是进加锁，退是解锁，通过管程对象管理

用户线程：自定义线程主线程结束了，用户线程还存在，则表示JVM还存在

 public class demo {     public static void main(String[] args) {         Thread a = new Thread(() -> {             System.out.println(Thread.currentThread().getName()+"::"+Thread.currentThread().isDaemon());             while (true){}         }, "a");          a.start();         System.out.println(Thread.currentThread().getName());     } }

守护线程：

ex:垃圾回收没有用户线程了，都是守护线程，JVM结束

 public class demo {     public static void main(String[] args) {         Thread a = new Thread(() -> {             System.out.println(Thread.currentThread().getName()+"::"+Thread.currentThread().isDaemon());             while (true){}         }, "a");         //设置子线程为守护线程         a.setDaemon(true);         a.start();         System.out.println(Thread.currentThread().getName());     } }

__EOF__

本文作者： xbhog

本文链接： https://www.cnblogs.com/xbhog/p/15679944.html

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