关于线程安全,线程锁我们经常会用到,但你的使用姿势正确不,反正我用错了好长一段时间而不自知。所以有了这篇博客总结下线程锁的正确打开姿势
废话不说看例子
一,对整个方法进行加锁
1,对整个方法进行加锁,不同线程访问同一个类的同一个对象
public class TestRunnable implements Runnable {
@Override
public synchronized void run() {
// TODO Auto-generated method stub
for(int i=0;i<10;i++)
{
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"---"+i);
}
}
}
public static void main(String[] args) { TestRunnable runnable=new TestRunnable(); Thread threadA=new Thread(runnable,"threadA"); threadA.start(); Thread threadB=new Thread(runnable,"threadB"); threadB.start(); }
运行结果:
threadA---0
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
2,对整个方法进行加锁,不同线程访问同一个类的不同对象
public class TestRunnable implements Runnable {
@Override
public synchronized void run() {
// TODO Auto-generated method stub
for(int i=0;i<10;i++)
{
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"---"+i);
}
}
}
public static void main(String[] args) { TestRunnable runnableA=new TestRunnable(); Thread threadA=new Thread(runnableA,"threadA"); threadA.start(); TestRunnable runnableB=new TestRunnable(); Thread threadB=new Thread(runnableB,"threadB"); threadB.start(); }
运行结果:
threadB---0
threadA---0
threadA---1
threadB---1
threadA---2
threadB---2
threadA---3
threadB---3
threadB---4
threadA---4
threadA---5
threadB---5
threadA---6
threadB---6
threadA---7
threadB---7
threadA---8
threadB---8
threadA---9
threadB---9
小结:对方法整体加锁的做法适用条件是 多个线程访问的必须是同一个类的同一个实例对象
一,对代码块进行加锁
1,对代码块进行加锁,加锁对象为当前类对象,不同线程访问同一个类的同一个对象
public class TestRunnable implements Runnable {
@Override
public void run() {
// TODO Auto-generated method stub
synchronized (TestRunnable.this) {
for (int i = 0; i < 10; i++) {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "---" + i);
}
}
}
}
public static void main(String[] args) { TestRunnable runnable=new TestRunnable(); Thread threadA=new Thread(runnable,"threadA"); threadA.start(); Thread threadB=new Thread(runnable,"threadB"); threadB.start(); }
运行结果:
threadA---0
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
2,对代码块进行加锁,加锁对象为当前类对象,不同线程访问同一个类的不同对象
public class TestRunnable implements Runnable { @Override public void run() { // TODO Auto-generated method stub synchronized (TestRunnable.this) { for (int i = 0; i < 10; i++) { try { Thread.sleep(200); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "---" + i); } } }}
public static void main(String[] args)
{
TestRunnable runnableA=new TestRunnable();
Thread threadA=new Thread(runnableA,"threadA");
threadA.start();
TestRunnable runnableB=new TestRunnable();
Thread threadB=new Thread(runnableB,"threadB");
threadB.start();
}
运行结果:
threadB---0
threadA---0
threadB---1
threadA---1
threadB---2
threadA---2
threadA---3
threadB---3
threadA---4
threadB---4
threadB---5
threadA---5
threadA---6
threadB---6
threadB---7
threadA---7
threadA---8
threadB---8
threadA---9
threadB---9
3,对代码块进行加锁,加锁对象为当前类(不是类对象哦),不同线程访问同一个类的同一个对象
public class TestRunnable implements Runnable {
@Override
public void run() {
// TODO Auto-generated method stub
synchronized (TestRunnable.class) {
for (int i = 0; i < 10; i++) {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "---" + i);
}
}
}
}
public static void main(String[] args) { TestRunnable runnable=new TestRunnable(); Thread threadA=new Thread(runnable,"threadA"); threadA.start(); Thread threadB=new Thread(runnable,"threadB"); threadB.start(); }
运行结果:
threadA---0
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
4,对代码块进行加锁,加锁对象为当前类(不是类对象哦),不同线程访问同一个类的不同对象
public class TestRunnable implements Runnable {
@Override
public void run() {
// TODO Auto-generated method stub
synchronized (TestRunnable.class) {
for (int i = 0; i < 10; i++) {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "---" + i);
}
}
}
}
public static void main(String[] args) { TestRunnable runnableA=new TestRunnable(); Thread threadA=new Thread(runnableA,"threadA"); threadA.start(); TestRunnable runnableB=new TestRunnable(); Thread threadB=new Thread(runnableB,"threadB"); threadB.start(); }
运行结果:
threadA---0
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
5,对代码块进行加锁,加锁对象为已赋值的变量,不同线程访问同一个类的同一个对象
public class TestRunnable implements Runnable {
@Override
public void run() {
// TODO Auto-generated method stub
synchronized ("test") {
for (int i = 0; i < 10; i++) {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "---" + i);
}
}
}
}
public static void main(String[] args) { TestRunnable runnable=new TestRunnable(); Thread threadA=new Thread(runnable,"threadA"); threadA.start(); Thread threadB=new Thread(runnable,"threadB"); threadB.start(); }
运行结果:
threadA---0
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
6,对代码块进行加锁,加锁对象为已赋值的变量,不同线程访问同一个类的不同对象
public class TestRunnable implements Runnable {
@Override
public void run() {
// TODO Auto-generated method stub
synchronized ("test") {
for (int i = 0; i < 10; i++) {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + "---" + i);
}
}
}
}
public static void main(String[] args) { TestRunnable runnableA=new TestRunnable(); Thread threadA=new Thread(runnableA,"threadA"); threadA.start(); TestRunnable runnableB=new TestRunnable(); Thread threadB=new Thread(runnableB,"threadB"); threadB.start(); }
运行结果:
threadA---0
threadA---1
threadA---2
threadA---3
threadA---4
threadA---5
threadA---6
threadA---7
threadA---8
threadA---9
threadB---0
threadB---1
threadB---2
threadB---3
threadB---4
threadB---5
threadB---6
threadB---7
threadB---8
threadB---9
小结:当对代码块进行加锁时,当加锁对象是一个确定值时(当前类,或者已赋值的变量) 不同线程访问同一个类的不同对象时也可以实现线程同步
最后奉上线程锁在实际开发中的应用----单例模式
1,懒汉式写法
public class Singleton {2,懒汉式写法升级版(双重校验锁) 性能优于第一种
private static Singleton instance;
private Singleton (){}
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
public class Singleton {
private static Singleton singleton;
private Singleton (){}
public static Singleton getSingleton() {
if (singleton == null) {
synchronized (Singleton.class) {
if (singleton == null) {
singleton = new Singleton();
}
}
}
return singleton;
}
}
public class Singleton {
private static Singleton instance = new Singleton();
private Singleton (){}
public static Singleton getInstance() {
return instance;
}
}