Java馬士兵高並發編程視頻學習筆記（一）

本文轉載自查看原文 2019-06-08 21:09 590 JDK/ 通用實踐/ 高並發/ 開發經驗/ 性能優化/ java經驗集錦/ 多線程/ 架構設計/ 工作總結

1.同一個資源，同步和非同步的方法可以同時調用

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先執行，如果不能同時調用那么t2是不能執行的，必須等t1結束，釋放鎖后才能調用，但這里t2確先執行了，所以是可以同時調用的。

2.對業務寫代碼進行加鎖，對讀代碼不進行加鎖，會產生臟讀

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.同線程內一個同步方法可以去調用另一個同步方法（重入鎖還有一種重入鎖就是子類調用父類的同步方法）

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.模擬一個簡單的死鎖

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>"如果出現這句話表示沒有死鎖"<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>"如果出現這句話表示沒有死鎖"<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.如果執行同步方法中出現異常，那么就會自動釋放鎖，如果不想釋放鎖，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關鍵字（無鎖同步）

volatile關鍵字每個線程都有自己的一小塊內存，執行的時候會把變量copy過來，修改了后在寫回對象，

執行m1方法的線程把 running讀到內存里，與此同時主線程也把running讀到內存，並進行修改，寫回對象為false

但是執行m1的線程里的內存一直都是true啊（因為太忙了沒空去刷新）所以會形成死循環，

volatile就是當running改了之后 *立馬去通知其他線程，你們記得去主存刷新一下，一刷新，running為false，退出while循環。

package com.dingyu;
/**
 * volatile關鍵字   每個線程都有自己的一小塊內存，執行的時候會把變量copy過來，修改了后在寫回對象，
 * 執行m1方法的線程把 running讀到內存里，與此同時主線程也把running讀到內存，並進行修改，寫回對象為false
 * 但是執行m1的線程里的內存一直都是true啊（因為太忙了沒空去刷新）所以會形成死循環，volatile就是當running改了之后
 * 立馬去通知其他線程，你們記得去主存刷新一下，一刷新，running為false，退出while循環。
 * @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 不能保證原子性不能替換synchronized

package com.dingyu;
/**

    
    
   
   
            
            voliatile 不能保證原子性 不能替換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.多個原子類的方法之間不具備原子性

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

    
    
   
   
            
            原子類 具有原子性，但兩個原子類的方法之間不具備原子性 
             
            @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;">兩個原子類的方法之間不具備原子性</span>

 count.incrementAndGet();
    }
}

}

9.原子類的不具備可見性

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.鎖是鎖在堆內存的那個對象上，而不是引用

package com.dingyu;
/**

    
    
   
   
            
            鎖是鎖在堆內存的那個對象上，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;">鎖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;">啟動一個線程 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;">引用變了</span>
    <span style="color: #0000ff;">new</span> Thread(() -&gt; changeReference.m1(),"t2").start();<span style="color: #008000;">//</span><span style="color: #008000;">啟動線程 t2</span>

 }
 }

11.不要鎖字符串常量

package com.dingyu;
/**
 * 不要鎖字符串常量
 * @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 讓線程暫停，釋放鎖， notify 喚醒線程，不釋放鎖

package com.dingyu2;
/**

    
    
   
   
            
            wait 讓線程暫停，釋放鎖， notify 喚醒線程，不釋放鎖 
             
            @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 但把鎖釋放了"<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();
}

}

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