08_死锁-产生与解决
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2022-04-17 16:06:18
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死锁——产生与解决
1、死锁
多个线程各自占用一些资源,并且相互等待其他线程占用的资源才能进行,而导致两个或多个线程都在等待对方释放资源,所以度停止执行了。
产生的原因:
过多的同步可能造成死锁
某一个同步块同时拥有两个以上对象的锁时,就可能发生死锁问题
死锁出现的情况:
package com.tsymq.thread.concurrnet;
public class DeadLock {
public static void main(String[] args) {
TeamMember tm1 = new TeamMember(1, "五五开");
TeamMember tm2 = new TeamMember(2, "蛇哥");
tm1.start();
tm2.start();
}
}
class AWM{}
class Scope8{}
class TeamMember extends Thread {
static AWM awm = new AWM();
static Scope8 scope8 = new Scope8();
private String name;
private int component;
public TeamMember(int component, String name) {
super(name);
this.name = name;
this.component = component;
}
@Override
public void run() {
pickup();
}
public void pickup(){
if (component == 1){
synchronized (awm){
System.out.println(this.getName() + "获得AWM!");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (scope8){
System.out.println(super.getName() + "获得8倍镜!");
}
}
} else {
synchronized (scope8){
System.out.println(super.getName() + "获得8倍镜!");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (awm){
System.out.println(this.getName() + "获得AWM!");
}
}
}
}
}
AWM和8倍镜都只有1个,一开始五五开拿到AWM,蛇哥拿到8倍镜,1秒钟后,五五开还想要一个8倍镜,而此时8倍镜还在蛇哥手中,所以只能等待,又过了1秒钟,蛇哥还想要AWM,可是AWM还在开哥手中,也只能等待,两个人互不想让,形成了死锁
解决办法:
不要放在同一个代码块中,不要锁套锁,可避免死锁发生
package com.tsymq.thread.concurrnet;
public class DeadLock {
public static void main(String[] args) {
TeamMember tm1 = new TeamMember(1, "五五开");
TeamMember tm2 = new TeamMember(2, "蛇哥");
tm1.start();
tm2.start();
}
}
class AWM{}
class Scope8{}
class TeamMember extends Thread {
static AWM awm = new AWM();
static Scope8 scope8 = new Scope8();
private String name;
private int component;
public TeamMember(int component, String name) {
super(name);
this.name = name;
this.component = component;
}
@Override
public void run() {
pickup();
}
public void pickup(){
if (component == 1){
synchronized (awm){
System.out.println(this.getName() + "获得AWM!");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// synchronized (scope8){
// System.out.println(super.getName() + "获得8倍镜!");
// }
}
synchronized (scope8){
System.out.println(super.getName() + "获得8倍镜!");
}
} else {
synchronized (scope8){
System.out.println(super.getName() + "获得8倍镜!");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// synchronized (awm){
// System.out.println(this.getName() + "获得AWM!");
// }
}
synchronized (awm){
System.out.println(this.getName() + "获得AWM!");
}
}
}
}
在五五开拿到AWM,蛇哥拿到8倍镜后,1秒钟后,开哥放弃了AWM,想要8倍镜,但是还在蛇哥手中,所以等待,又1秒钟后,蛇哥放弃了8倍镜,想要AWM,此时开哥已经放弃了AWM,蛇哥拿到了AWM,由于蛇哥已经放弃了8倍镜,所以开哥成功拿到8倍镜
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