Java马士兵高并发编程视频学习笔记（一）

1.同一个资源，同步和非同步的方法可以同时调用

package com.dingyu;
public class Y {

public synchronized void m1() {

System.out.println(Thread.currentThread().getName() + " m1 begin---------");

try {

Thread.sleep(5000);

} catch (InterruptedException e) {

// TODO Auto-generated catch block

            e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + " m1 end---------");

}
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m2() {
    System.out.println(Thread.currentThread().getName() </span>+ " m2 begin---------"<span style="color: #000000;">);
    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(</span>5000<span style="color: #000000;">);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        </span><span style="color: #008000;">//</span><span style="color: #008000;"> TODO Auto-generated catch block</span>

            e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + " m2 end---------");

}

public static void main(String[] args) {

Y t = new Y();

//        new Thread(()->t.m1(),"t1").start();

//        new Thread(()->t.m2(),"t2").start();

new Thread(new Runnable() {
        @Override
        </span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> run() {
            t.m1();
            
        }
    },</span>"t1"<span style="color: #000000;">).start();;
</span><span style="color: #0000ff;">new</span> Thread(<span style="color: #0000ff;">new</span><span style="color: #000000;"> Runnable() {
        
        @Override
        </span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> run() {
            t.m2();
            
        }
    },</span>"t2"<span style="color: #000000;">).start();;
}

}

可以看到t1先执行，如果不能同时调用那么t2是不能执行的，必须等t1结束，释放锁后才能调用，但这里t2确先执行了，所以是可以同时调用的。

2.对业务写代码进行加锁，对读代码不进行加锁，会产生脏读

　　

package com.dingyu;
public class U {

private String name;

private double banlance;
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">synchronized</span> <span style="color: #0000ff;">void</span> set(String name, <span style="color: #0000ff;">double</span><span style="color: #000000;"> balance) {
    </span><span style="color: #0000ff;">this</span>.name =<span style="color: #000000;"> name;
    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(</span>5000<span style="color: #000000;">);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        e.printStackTrace();
    }
    </span><span style="color: #0000ff;">this</span>.banlance =<span style="color: #000000;"> balance;
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">double</span><span style="color: #000000;"> getBalance() {
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> banlance;
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    U u </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> U();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt; u.set("zhangsan", 500<span style="color: #000000;">)).start();
    System.out.println(u.getBalance());
    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(</span>5000<span style="color: #000000;">);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(u.getBalance());
}

}

3.同线程内一个同步方法可以去调用另一个同步方法（重入锁 还有一种重入锁就是子类调用父类的同步方法）

package com.dingyu;
public class I {

public synchronized void m1() {

System.out.println("m1 start");

m2();

System.out.println("m1 end");

}
</span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">synchronized</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m2() {
    System.out.println(</span>"m2 start"<span style="color: #000000;">);
    System.out.println(</span>"m2 end"<span style="color: #000000;">);
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    I i </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> I();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt;<span style="color: #000000;"> i.m1()).start();
}

}

4.模拟一个简单的死锁

package com.dingyu;
public class DeadLock {

private Object o1 = new Object();

private Object o2 = new Object();
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (o1) {
        </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
            Thread.sleep(</span>10000<span style="color: #000000;">);
        } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
            e.printStackTrace();
        }
        
        </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (o2) {
            System.out.println(</span>"如果出现这句话表示没有死锁"<span style="color: #000000;">);
        }
    }
    
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m2() {
    </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;">(o2) {
        
        </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (o1) {
            System.out.println(</span>"如果出现这句话表示没有死锁"<span style="color: #000000;">);
        }
        
    }
    
}
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    DeadLock deadLock</span>=<span style="color: #0000ff;">new</span><span style="color: #000000;"> DeadLock();
    </span><span style="color: #0000ff;">new</span> Thread(()-&gt;<span style="color: #000000;">deadLock.m1()).start();
    </span><span style="color: #0000ff;">new</span> Thread(()-&gt;<span style="color: #000000;">deadLock.m2()).start();
}

}

5.如果执行同步方法中出现异常，那么就会自动释放锁，如果不想释放锁，加上try catch

package com.dingyu;
public class ReleaseLock {

private int count = 0;

private int i = 0;
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">synchronized</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">while</span> (<span style="color: #0000ff;">true</span><span style="color: #000000;">) {
        System.out.println(Thread.currentThread().getName() </span>+ " " + count++<span style="color: #000000;">);
        </span><span style="color: #0000ff;">if</span> (count % 10 == 0<span style="color: #000000;">)
            i </span>= 1 / 0<span style="color: #000000;">;
    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    ReleaseLock releaseLock </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> ReleaseLock();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt; releaseLock.m1(), "t1"<span style="color: #000000;">).start();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt; releaseLock.m1(), "t2"<span style="color: #000000;">).start();
}

}

 6.volatile关键字（无锁同步）

volatile关键字 每个线程都有自己的一小块内存，执行的时候会把变量copy过来，修改了后在写回对象，

执行m1方法的线程把 running读到内存里，与此同时主线程也把running读到内存，并进行修改，写回对象为false

但是执行m1的线程里的内存一直都是true啊（因为太忙了没空去刷新）所以会形成死循环，

volatile就是当running改了之后 *立马去通知其他线程，你们记得去主存刷新一下，一刷新，running为false，退出while循环。

package com.dingyu;
/**
 * volatile关键字   每个线程都有自己的一小块内存，执行的时候会把变量copy过来，修改了后在写回对象，
 * 执行m1方法的线程把 running读到内存里，与此同时主线程也把running读到内存，并进行修改，写回对象为false
 * 但是执行m1的线程里的内存一直都是true啊（因为太忙了没空去刷新）所以会形成死循环，volatile就是当running改了之后
 * 立马去通知其他线程，你们记得去主存刷新一下，一刷新，running为false，退出while循环。
 * @author dingyu
 *
 */
public class VolatileDemo {
    private volatile boolean running = true;
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    System.out.println(</span>"m1 start"<span style="color: #000000;">);
    </span><span style="color: #0000ff;">while</span><span style="color: #000000;"> (running) {
        
    }
    System.out.println(</span>"m1 end"<span style="color: #000000;">);
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    VolatileDemo volatileDemo </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> VolatileDemo();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt;<span style="color: #000000;"> volatileDemo.m1()).start();
    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(</span>1000<span style="color: #000000;">);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        e.printStackTrace();
    }
    volatileDemo.running </span>= <span style="color: #0000ff;">false</span><span style="color: #000000;">;

}

}

7.voliatile 不能保证原子性 不能替换synchronized

package com.dingyu;
/**

voliatile 不能保证原子性 不能替换synchronized

@author dingyu


*/

public class VolatileDemo02 {

public volatile int count = 0;
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">for</span> (<span style="color: #0000ff;">int</span> i = 0; i &lt;= 10000; i++<span style="color: #000000;">)
        count</span>++<span style="color: #000000;">;
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    VolatileDemo02 volatileDemo02 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> VolatileDemo02();
    </span><span style="color: #0000ff;">for</span> (<span style="color: #0000ff;">int</span> i = 0; i &lt; 3; i++<span style="color: #000000;">) {
        </span><span style="color: #0000ff;">new</span> Thread(() -&gt;<span style="color: #000000;"> volatileDemo02.m1()).start();
    }
    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(</span>5000<span style="color: #000000;">);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(volatileDemo02.count);
}

}

 8.多个原子类的方法之间不具备原子性

package com.dingyu;
import java.util.concurrent.atomic.AtomicInteger;
/**

原子类 具有原子性，但两个原子类的方法之间不具备原子性

@author dingyu


*/

public class AtomicDemo {

private AtomicInteger count = new AtomicInteger();
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">for</span> (<span style="color: #0000ff;">int</span> i = 0; i &lt; 100; i++<span style="color: #000000;">) {            
        count.incrementAndGet();
        </span><span style="color: #008000;">//</span><span style="color: #008000;">两个原子类的方法之间不具备原子性</span>

            count.incrementAndGet();
    }
}

}

9.原子类的不具备可见性

package com.dingyu;
import java.util.concurrent.atomic.AtomicBoolean;
public class AtomicDemo02 {

public AtomicBoolean running = new AtomicBoolean(true);
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">while</span><span style="color: #000000;"> (running.get()) {

    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    AtomicDemo02 demo02 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> AtomicDemo02();
    </span><span style="color: #0000ff;">new</span> Thread(()-&gt;<span style="color: #000000;">demo02.m1()).start();
    demo02.running.set(</span><span style="color: #0000ff;">false</span><span style="color: #000000;">);
}

}

10.锁是锁在堆内存的那个对象上，而不是引用

package com.dingyu;
/**

锁是锁在堆内存的那个对象上，而不是引用

@author dingyu


*/

public class ChangeReference {

public Object o = new Object();
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #008000;">//</span><span style="color: #008000;">锁o</span>
    <span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (o) {
        </span><span style="color: #0000ff;">while</span> (<span style="color: #0000ff;">true</span><span style="color: #000000;">) {
            </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
                Thread.sleep(</span>1000<span style="color: #000000;">);
            } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName());
        }
    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    ChangeReference changeReference </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> ChangeReference();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt; changeReference.m1(), "t1").start();<span style="color: #008000;">//</span><span style="color: #008000;">启动一个线程 叫t1</span>
    <span style="color: #0000ff;">try</span><span style="color: #000000;"> {
        Thread.sleep(</span>3000<span style="color: #000000;">);
    } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
        e.printStackTrace();
    }
    changeReference.o </span>= <span style="color: #0000ff;">new</span> Object();<span style="color: #008000;">//</span><span style="color: #008000;">引用变了</span>
    <span style="color: #0000ff;">new</span> Thread(() -&gt; changeReference.m1(),"t2").start();<span style="color: #008000;">//</span><span style="color: #008000;">启动线程 t2</span>

    }

}

 11.不要锁字符串常量

package com.dingyu;
/**
 * 不要锁字符串常量
 * @author dingyu
 *
 */
public class SynchronizedString {
    private String s1 = "hello";
    private String s2 = "hello";
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (s1) {
        </span><span style="color: #0000ff;">while</span>(<span style="color: #0000ff;">true</span><span style="color: #000000;">) {}
    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m2() {
    </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (s2) {
        System.out.println(</span>"m2 start"<span style="color: #000000;">);
    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    SynchronizedString synchronizedString </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> SynchronizedString();
    </span><span style="color: #0000ff;">new</span> Thread(()-&gt;<span style="color: #000000;">synchronizedString.m1()).start();
    </span><span style="color: #0000ff;">new</span> Thread(()-&gt;<span style="color: #000000;">synchronizedString.m2()).start();
}

}

12.wait 让线程暂停，释放锁， notify 唤醒线程，不释放锁

package com.dingyu2;
/**

wait 让线程暂停，释放锁， notify 唤醒线程，不释放锁

@author dingyu


*/

public class WaitAndNotyifyDemo {

private volatile int count = 0;

private Object lock = new Object();
</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m1() {
    </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (lock) {
        System.out.println(</span>"m1 start"<span style="color: #000000;">);
        </span><span style="color: #0000ff;">for</span> (<span style="color: #0000ff;">int</span> i = 0; i &lt; 10; i++<span style="color: #000000;">) {
            count</span>++<span style="color: #000000;">;
            System.out.println(count);
            </span><span style="color: #0000ff;">if</span> (count == 5<span style="color: #000000;">) {
                lock.notify();
                </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
                    lock.wait();
                } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }

    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> m2() {
    </span><span style="color: #0000ff;">synchronized</span><span style="color: #000000;"> (lock) {
        System.out.println(</span>"m2 start"<span style="color: #000000;">);
        </span><span style="color: #0000ff;">if</span> (count != 5<span style="color: #000000;">) {
            </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {
                System.out.println(</span>"m2 在等着 但把锁释放了"<span style="color: #000000;">);
                lock.wait();                    
            } </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(</span>"m2 end"<span style="color: #000000;">);
        lock.notify();
    }
}

</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> main(String[] args) {
    WaitAndNotyifyDemo waitAndNotyifyDemo </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> WaitAndNotyifyDemo();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt;<span style="color: #000000;"> waitAndNotyifyDemo.m2()).start();
    </span><span style="color: #0000ff;">new</span> Thread(() -&gt;<span style="color: #000000;"> waitAndNotyifyDemo.m1()).start();
}

}

原文地址：https://www.cnblogs.com/dddyyy/p/9965836.html