当前位置：网站首页>JUC (1) threads and processes, concurrency and parallelism, thread state, locks, producers and consumers

JUC (1) threads and processes, concurrency and parallelism, thread state, locks, producers and consumers

2022-08-04 10:31:00 【51CTO】

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_i++

1、线程和进程

进程：一个程序,微信、qq、、、程序的集合.（一个进程包含多个线程,至少包含一个线程.java默认有两个线程：主线程（main）、垃圾回收线程（GC）
线程：runnable、thread 、callable
java开不了线程,在源码中可以看出,调用的是底层的方法

       
       private native void start0();
      
1.

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_i++_02

2、并发和并行

并发：交替
并行：同时（同一个时间）
并发编程的本质：充分利用cpu的资源

3、线程的状态

看源码

       
       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 <tt>Object.wait()</tt>
       
         * on an object is waiting for another thread to call
       
         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
       
         * that object. A thread that has called <tt>Thread.join()</tt>
       
         * 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;
       
    }
      
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.

新生
运行
阻塞
等待,（死死的等）
超时等待
终止

4、sleep和wait的区别

sleep来自thread.wait来自object
wait会释放锁,sleep不会释放锁
wait只能在同步代码块中,sleep可以在任意地方睡

5、Lock锁

Lock接口

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_java_03

public interface Lock
Lock实现提供比使用synchronized方法和语句可以获得的更广泛的锁定操作. 它们允许更灵活的结构化,可能具有完全不同的属性,并且可以支持多个相关联的对象Condition .
锁是用于通过多个线程控制对共享资源的访问的工具. 通常,锁提供对共享资源的独占访问：一次只能有一个线程可以获取锁,并且对共享资源的所有访问都要求首先获取锁. 但是,一些锁可能允许并发访问共享资源,如ReadWriteLock的读锁.

使用synchronized方法或语句提供对与每个对象相关联的隐式监视器锁的访问,但是强制所有锁获取和释放以块结构的方式发生：当获取多个锁时,它们必须以相反的顺序被释放,并且所有的锁都必须被释放在与它们相同的词汇范围内.

虽然synchronized方法和语句的范围机制使得使用监视器锁更容易编程,并且有助于避免涉及锁的许多常见编程错误,但是有时您需要以更灵活的方式处理锁. 例如,用于遍历并发访问的数据结构的一些算法需要使用“手动”或“链锁定”：您获取节点A的锁定,然后获取节点B,然后释放A并获取C,然后释放B并获得D等. 所述的实施方式中Lock接口通过允许获得并在不同的范围释放的锁,并允许获得并以任何顺序释放多个锁使得能够使用这样的技术.

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_java_04

synchronized和lock的区别

1、synchronized内置的java关键字,lock是一个java类
2、synchronized 无法判断获取锁的状态,lock锁可以判断是否获取到了锁
3、synchronized会自动释放锁,lock必须要手动释放锁,如果不释放锁,死锁
4、synchronized 线程1获得锁,阻塞,线程2 傻傻的等.lock锁就不一定会等下去;会试图获取锁
5、synchronized 可重入锁,不可以中断,非公平：lock,可重入锁可以判断锁,非公平
6、synchronized 适合锁少量的代码同步问题,lock适合锁大量的同步代码

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_java_05

6、买票问题

7、生产者和消费者问题

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_i++_06

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_i++_07

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_javascript_08

8、使用condition替换synchronized

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_java_09

JUC（1）线程和进程、并发和并行、线程的状态、lock锁、生产者和消费者问题_javascript_10

修改后的代码

       
       package com.pc;
       
import java.util.concurrent.locks.Condition;
       
import java.util.concurrent.locks.Lock;
       
import java.util.concurrent.locks.ReentrantLock;
       
/**
       
 * 线程之间的通信,生产者和消费者问题
       
 */
       
public class PC {
       
    public static void main(String[] args) {
       
        Data data = new Data();
       
        new Thread(()->{
       
            for (int i = 0; i < 5; i++) {
       
                try {
       
                    data.increment();
       
                } catch (InterruptedException e) {
       
                    e.printStackTrace();
       
                }
       
            }
       
        },"A").start();
       
        new Thread(()->{
       
            for (int i = 0; i < 5; i++) {
       
                try {
       
                    data.decrement();
       
                } catch (InterruptedException e) {
       
                    e.printStackTrace();
       
                }
       
            }
       
        },"B").start();
       
        new Thread(()->{
       
            for (int i = 0; i < 5; i++) {
       
                try {
       
                    data.increment();
       
                } catch (InterruptedException e) {
       
                    e.printStackTrace();
       
                }
       
            }
       
        },"C").start();
       
        new Thread(()->{
       
            for (int i = 0; i < 5; i++) {
       
                try {
       
                    data.decrement();
       
                } catch (InterruptedException e) {
       
                    e.printStackTrace();
       
                }
       
            }
       
        },"D").start();
       
    }
       
}
       
//等待,业务,通知
       
class Data {
       
    //资源类
       
    private int num = 0;
       
    Lock lock = new ReentrantLock();
       
    Condition condition = lock.newCondition();
       
    /**
       
     * condition.await();//等待
       
     * condition.signalAll();//通知
       
     */
       
    //增加操作
       
    public void increment() throws InterruptedException {
       
        try {
       
            lock.lock();
       
            while (num != 0) {
       
                //等待
       
                condition.await();
       
            }
       
            num++;
       
            System.out.println(Thread.currentThread().getName() + "=>" + num);
       
            //通知
       
            condition.signalAll();
       
        } finally {
       
            lock.unlock();
       
        }
       
    }
       
    //减少操作
       
    public void decrement() throws InterruptedException {
       
        try {
       
            //第一步上锁
       
            lock.lock();
       
            while (num == 0) {
       
                //等待
       
                condition.await();
       
            }
       
            num--;
       
            System.out.println(Thread.currentThread().getName() + "=>" + num);
       
            //通知
       
            condition.signalAll();
       
        } finally {
       
            lock.unlock();
       
        }
       
    }
       
}
      
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
111.