JUC并发编程(一)

因为内容太多了，所以将其拆分为以下内容

• JUC并发编程(一)（当前）
• JUC并发编程(二)
• JUC并发编程(三)
• JUC并发编程(四)
• JUC并发编程(五)

参考

https://www.bilibili.com/video/BV1B7411L7tE

多线程进阶=>JUC并发编程

JDK下的

• java.util.concurrent
• java.util.concurrent.atomic
• java.util.concurrent.locks
• java.util.fuction

回顾多线程

public class Test1 {
    public static void main(String[] args) {
        //获得CPU核数
        System.out.println(Runtime.getRuntime().availableProcessors());
    }
}

线程状态

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;
}

中文对应

Enum Constant and Description
BLOCKED 一个线程的线程状态阻塞等待监视器锁定。
NEW 线程尚未启动的线程状态。
RUNNABLE 可运行线程的线程状态。
TERMINATED 终止线程的线程状态。
TIMED_WAITING 具有指定等待时间的等待线程的线程状态。
WAITING 等待线程的线程状态

Lock锁

传统的synchronized

public class Test1 {
    public static void main(String[] args) {
        Ticket ticket=new Ticket();

        new Thread(()->{
            for (int i = 0; i < 40; i++) {
                ticket.sale();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 40; i++) {
                ticket.sale();
            }
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 40; i++) {
                ticket.sale();
            }
        },"C").start();
    }
}
class Ticket{
    private int number=30;

    public synchronized void sale(){
        if(number>0){
            number--;
            System.out.println(Thread.currentThread().getName()+"当前票数"+number);
        }
    }
}

Lock接口

• 随着这种增加的灵活性，额外的责任。 没有块结构化锁定会删除使用synchronized方法和语句发生的锁的自动释放。 在大多数情况下，应使用以下惯用语：

  Lock l = ...; l.lock(); try { // access the resource protected by this lock } finally { l.unlock(); }

  当在不同范围内发生锁定和解锁时，必须注意确保在锁定时执行的所有代码由try-finally或try-catch保护，以确保在必要时释放锁定。

public class Test2 {
    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();
    }
}

class Ticket2 {
    private int number = 30;
    //1.new ReentrantLock();
    Lock lock = new ReentrantLock();

    public void sale() {
        //2.lock();
        lock.lock();
        try {
            if (number > 0) {
                number--;
                System.out.println(Thread.currentThread().getName() + "当前票数" + number);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //3.unlock();
            lock.unlock();
        }
    }
}

synchronized 与 lock 区别

1. Synchronized 内置的Jva关键字， Lock 是一个Java类
2. Synchronized 无法判断获取锁的状态，Lock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,阳塞).线程2 (等待,使使的等) ；Lock锁就不一定会等待下去；
5. Synchronized可重入锁 ，不可以中断的，非公平；Lock，可重入锁,可以判断锁,非公平(可以自己设置) ；
6. Synchronied 适合锁少量的代码同步问题 ，Lock适合锁大量的同步代码！

锁是什么，如何判断锁的是谁？

因为内容太多了，所以将其拆分为以下内容

• JUC并发编程(一)（当前）
• JUC并发编程(二)
• JUC并发编程(三)
• JUC并发编程(四)
• JUC并发编程(五)