一，环境
idea
二.什么是线程安全问题，为什么会有线程安全问题
线程安全问题产生于多个线程同时访问共享资源（通常查询不会产生）
三.举例
假如我现在想讲一个数循化加一，最终增加到1000.但是需要用5个线程来加
class Count
implements Runnable{
private int count=1
;
public void run() {
while (count<=1000
){
count=count+1
;
System.out.println(Thread.currentThread().getName()+",count:"+
count);
}
}
}
public class ThreadTest {
public static void main(String[] args) {
Count count=
new Count();
Thread t1=
new Thread(count,"线程一"
);
Thread t2=
new Thread(count,"线程二"
);
Thread t3=
new Thread(count,"线程三"
);
Thread t4=
new Thread(count,"线程四"
);
Thread t5=
new Thread(count,"线程五"
);
t1.start();
t2.start();
t3.start();
t4.start();
t5.start();
}
}
结果：
代码显示:最多会增加到1000循环就会结束那么为什么会出现1001呢！！
由于现在是多线程增加，有可能当count增加到999的时候同时又两个线程都进入了while循环里，然后就连续增加了两次
那么怎么解决呢！！！
四.使用锁来解决
4.1同步代码块
class Count
implements Runnable{
private volatile int count=1
;
private static Object oj =
new Object();
public void run() {
while (count<=1000
){
synchronized (oj) {
//oj就是锁对象可以为任意对象也可为this
if(count<=1000
) {
count = count + 1
;
System.out.println(Thread.currentThread().getName() + ",count:" +
count);
}
}
}
}
}
public class ThreadTest {
public static void main(String[] args) {
Count count=
new Count();
Thread t1=
new Thread(count,"线程一"
);
Thread t2=
new Thread(count,"线程二"
);
Thread t3=
new Thread(count,"线程三"
);
Thread t4=
new Thread(count,"线程四"
);
Thread t5=
new Thread(count,"线程五"
);
t1.start();
t2.start();
t3.start();
t4.start();
t5.start();
}
}
4.2使用同步方法
class Count
implements Runnable{
private volatile int count=1
;
private static Object oj =
new Object();
public void run() {
while (count<=1000
){
sole();
}
}
public synchronized void sole(){
//这把锁的锁对象就是this
if(count<=1000
) {
count = count + 1
;
System.out.println(Thread.currentThread().getName() + ",count:" +
count);
}
}
}
public class ThreadTest {
public static void main(String[] args) {
Count count=
new Count();
Thread t1=
new Thread(count,"线程一"
);
Thread t2=
new Thread(count,"线程二"
);
Thread t3=
new Thread(count,"线程三"
);
Thread t4=
new Thread(count,"线程四"
);
Thread t5=
new Thread(count,"线程五"
);
t1.start();
t2.start();
t3.start();
t4.start();
t5.start();
}
}
转载于:https://www.cnblogs.com/wy0119/p/8999163.html
