对同一个对象进行多线程操作时，如何保证线程执行结果的一致性？我们需要对线程操作对象加同步锁。（这是一道面试题）
需求描述
1-20个数字
a线程打印奇数：1，3，5，7，9，11，13，15，17，19
b线程打印偶数：2，4，6，8，10，12，14，16，18，20
c线程在ab两个线程执行完了之后打印结果：[success]。
线程代码实现
num.java
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package com.boonya.thread.test;
/** * @classname: num * @description: todo(加锁计算对象) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 22:47 */ public class num { int value= 1 ; } |
athread.java
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package com.boonya.thread.test;
/** * @classname: athread * @description: todo(奇数线程) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 22:26 */ public class athread implements runnable{
num num;
public athread(num num){ this .num=num; }
public void run() { while (num.value< 20 ){ synchronized (num){ if (num.value% 2 != 0 ){ system.out.println( "athread:" + num.value); num.value++; } } }
} } |
bthread.java
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package com.boonya.thread.test;
/** * @classname: bthread * @description: todo(偶数线程) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 22:26 */ public class bthread implements runnable {
num num;
public bthread(num num){ this .num=num; }
public void run() { while (num.value<= 20 ){ synchronized (num){ if (num.value% 2 == 0 ){ system.out.println( "bthread:" + num.value); num.value++; } } } } } |
cthread.java
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package com.boonya.thread.test;
/** * @classname: cthread * @description: todo(等待结果线程) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 22:26 */ public class cthread implements runnable {
num num;
public cthread(num num){ this .num=num; }
public void run() { while (num.value< 20 ){ try { thread.sleep( 1 ); } catch (interruptedexception e) { e.printstacktrace(); } } system.out.println( "cthread:success!" ); } } |
maintest.java
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package com.boonya.thread.test;
import java.util.arraylist; import java.util.list;
/** * @classname: maintest * @description: todo(线程测试) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 21:54 */ public class maintest {
public static void main(string[] args) { num num= new num(); thread a= new thread( new athread(num)); thread b= new thread( new bthread(num)); thread c= new thread( new cthread(num)); a.start(); b.start(); c.start(); } } |
测试结果
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"c:\program files\java\jdk1.8.0_121\bin\java" "-javaagent:c:\users\boonya\appdata\roaming\jetbrains\intellij idea 2017.2.5\lib\idea_rt.jar=51911:c:\users\boonya\appdata\roaming\jetbrains\intellij idea 2017.2.5\bin" -dfile.encoding=utf- 8 -classpath "c:\program files\java\jdk1.8.0_121\jre\lib\charsets.jar;c:\program files\java\jdk1.8.0_121\jre\lib\deploy.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\access-bridge-64.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\cldrdata.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\dnsns.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\jaccess.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\jfxrt.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\localedata.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\nashorn.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\sunec.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\sunjce_provider.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\sunmscapi.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\sunpkcs11.jar;c:\program files\java\jdk1.8.0_121\jre\lib\ext\zipfs.jar;c:\program files\java\jdk1.8.0_121\jre\lib\javaws.jar;c:\program files\java\jdk1.8.0_121\jre\lib\jce.jar;c:\program files\java\jdk1.8.0_121\jre\lib\jfr.jar;c:\program files\java\jdk1.8.0_121\jre\lib\jfxswt.jar;c:\program files\java\jdk1.8.0_121\jre\lib\jsse.jar;c:\program files\java\jdk1.8.0_121\jre\lib\management-agent.jar;c:\program files\java\jdk1.8.0_121\jre\lib\plugin.jar;c:\program files\java\jdk1.8.0_121\jre\lib\resources.jar;c:\program files\java\jdk1.8.0_121\jre\lib\rt.jar;c:\users\boonya\desktop\javaalgorithm\target\test-classes;c:\users\boonya\desktop\javaalgorithm\target\classes" com.boonya.thread.test.maintest athread: 1 bthread: 2 athread: 3 bthread: 4 athread: 5 bthread: 6 athread: 7 bthread: 8 athread: 9 bthread: 10 athread: 11 bthread: 12 athread: 13 bthread: 14 athread: 15 bthread: 16 athread: 17 bthread: 18 athread: 19 bthread: 20 cthread:success!
process finished with exit code 0 |
注意：synchronized 作为方法块使用时需要只能对对象加锁，不能是常用数据类型。
ab线程改进:使用线程等待和通知
athread.java
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package com.boonya.thread.test;
/** * @classname: athread * @description: todo(奇数线程) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 22:26 */ public class athread implements runnable{
num num;
public athread(num num){ this .num=num; }
public void run() { while (num.value< 20 ){ synchronized (num){ if (num.value% 2 != 0 ){ system.out.println( "athread:" + num.value); num.value++; //num.notify(); num.notifyall(); } else { try { num.wait(); } catch (interruptedexception e) { e.printstacktrace(); } } } }
} } |
bthread.java
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package com.boonya.thread.test;
/** * @classname: bthread * @description: todo(偶数线程) * @author: pengjunlin * @motto: 学习需要毅力，那就秀毅力 * @date 2019-01-14 22:26 */ public class bthread implements runnable {
num num;
public bthread(num num){ this .num=num; }
public void run() { while (num.value<= 20 ){ synchronized (num){ if (num.value% 2 == 0 ){ system.out.println( "bthread:" + num.value); num.value++; //num.notify(); num.notifyall(); } else { try { num.wait(); } catch (interruptedexception e) { e.printstacktrace(); } } } } } } |
注：线程等待和通知的操作是节省cpu运算的一种方式，避免cpu空转（线程方法一直不停地跑类似于死循环是很可怕的），如果是要让线程停下来需要调用线程的wait()。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。
原文链接：https://blog.csdn.net/boonya/article/details/86485504
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