线程基础知识05 synchronized类锁和对象锁演示
2024-09-08 18:52:54
1 简介
synchronized在方法内,同步代码块,传入对象,使用的是对象锁,传入class对象,使用的是类锁
作用于普通方法,也是对象锁,当前对象
作用于静态方法,是类锁
2 同步方法示例
2.1两个synchronized 修饰的普通方法
public class SychTest1 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){ //相当于synchromized(this)
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start();
//等待200
try { Thread.sleep(200); } catch (InterruptedException e)</span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendMsg();
}).start();
}
}
执行结果
MSG
2.2两个synchronized 修饰的普通方法,sendEmail睡了2秒
public class SychTest2 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
</span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendMsg();
}).start();
}
}
执行结果,发现第一个线程调用的sendEmail方法虽然等待了2秒,还是先打印,因为它先获取了锁,第二个线程只能等待。它们竞争的是同一个锁对象p
MSG
2.3一个同步方法,一个普通方法
public class SychTest3 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
</span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); } </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendMsg();
}).start();
}
}
执行结果
MSG
2.4两个同步方法,但是是两个不同的对象p和p2去调用同步方法
public class SychTest4 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); Phone p2 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); } </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p2.sendMsg();
}).start();
}
}
执行结果,持有的是不同的锁对象p和p2
MSG
2.5两个静态同步方法
public class SychTest5 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){ //相当于synchronized(Phone.class)
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); } </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendMsg();
}).start();
}
}
执行结果,持有的是同一个类锁
MSG
2.6 两个静态同步方法,两个对象p和p2去调用
public class SychTest6 {//?<span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone();
Phone p2 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); } </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p2.sendMsg();
}).start();
}
}
执行结果,持有的是同一个类锁,和哪个对象去调用无关
MSG
2.7一个静态同步,一个非静态同步
public class SychTest7 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); } </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendMsg();
}).start();
}
}
执行结果,一个持有类锁,一个持有对象锁
MSG
2.8一个静态同步方法,一个非静态同步方法,两个对象去调用
public class SychTest8 {</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> Phone{
synchronized </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">void</span><span style="color: #000000;"> sendEmail(){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">2000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">EMAIL</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
synchronized </span><span style="color: #0000ff;">void</span><span style="color: #000000;"> sendMsg(){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">MSG</span><span style="color: #800000;">"</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) { Phone p </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); Phone p2 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> Phone(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p.sendEmail();
}).start(); </span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">200</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); } </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
p2.sendMsg();
}).start();
}
}
执行结果,一个持有类锁,一个持有对象锁
MSG
3 同步代码示例
3.1传入class对象
public class SychTest13 {</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> synchronized <span style="color: #0000ff;">void</span><span style="color: #000000;"> aa() {
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">aaa</span><span style="color: #800000;">"</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) throws InterruptedException { </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
synchronized (SychTest13.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">1000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">aaaaaaaaaaaa</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
}).start(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
synchronized (SychTest13.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">bbbbbbbbbb</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
}).start();
}
}
执行结果
aaaaaaaaaaaa
bbbbbbbbbbb
3.2传入同一个对象t1
public class SychTest14 {</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> synchronized <span style="color: #0000ff;">void</span><span style="color: #000000;"> aa() {
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">aaa</span><span style="color: #800000;">"</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) throws InterruptedException {
SychTest13 t1 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> SychTest13();
</span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
synchronized (t1){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">1000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">aaaaaaaaaaaa</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
}).start(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
synchronized (t1){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">bbbbbbbbbb</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
}).start();
}
}
执行结果
aaaaaaaaaaaa
bbbbbbbbbbb
3.3传入对象t1和t2
public class SychTest15 {</span><span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> synchronized <span style="color: #0000ff;">void</span><span style="color: #000000;"> aa() {
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">aaa</span><span style="color: #800000;">"</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) throws InterruptedException {
SychTest13 t1 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> SychTest13();
SychTest13 t2 </span>= <span style="color: #0000ff;">new</span><span style="color: #000000;"> SychTest13();
</span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
synchronized (t1){
</span><span style="color: #0000ff;">try</span> { Thread.sleep(<span style="color: #800080;">1000</span>); } <span style="color: #0000ff;">catch</span><span style="color: #000000;"> (InterruptedException e) { e.printStackTrace(); }
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">aaaaaaaaaaaa</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
}).start(); </span><span style="color: #0000ff;">new</span> Thread(()-><span style="color: #000000;">{
synchronized (t2){
System.</span><span style="color: #0000ff;">out</span>.println(<span style="color: #800000;">"</span><span style="color: #800000;">bbbbbbbbbb</span><span style="color: #800000;">"</span><span style="color: #000000;">);
}
}).start();
}
}
执行结果
bbbbbbbbbb
aaaaaaaaaaaa
4 注意事项
4.1 异常
锁会被释放,其它线程可能进来继续执行。
会出现数据不一致的情况,多个servlet线程访问同一个资源时,如果第一个线程抛出异常,其他线程就会进入同步代码块,有可能会访问到异常产生时的数据(异常产生的数据很可能是不对的),出现数据不一致的情况
4.2 锁对象
synchronized (obj),obj不要用String、常量、基本数据类型。
因为使用字符串、常量,你可以使用,其它人也可以使用,你们很可能都不知道对方使用了,那么就有问题了
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