锁的理解
1、公平锁与非公平锁
公平锁：不能够插队，必须按照先来后到的顺序执行
非公平锁：可以插队（默认都是非公平锁）
lock锁对应的非公平锁与公平锁的源码
ReentrantLock lock = new ReentrantLock();
public ReentrantLock() {
sync = new NonfairSync();
}
ReentrantLock lock = new ReentrantLock(true);
public ReentrantLock(boolean fair) {
sync = fair ? new FairSync() : new NonfairSync();
}
2、可重入锁
synchronized
package com.zkw.JUC并发编程.lock;
public class Demon01 {
public static void main(String[] args) {
Phone phone = new Phone();
new Thread(()->{
phone.sms();
},"A").start();
new Thread(()->{
phone.sms();
},"B").start();
}
}
class Phone{
public synchronized void sms(){
System.out.println(Thread.currentThread().getName()+"--> sms()");
call();
}
public synchronized void call(){
System.out.println(Thread.currentThread().getName()+"--> call()");
}
}
Lock
package com.zkw.JUC并发编程.lock;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Demon02 {
public static void main(String[] args) {
Phone2 phone = new Phone2();
new Thread(()->{
phone.sms();
},"A").start();
new Thread(()->{
phone.sms();
},"B").start();
}
}
class Phone2{
Lock lock = new ReentrantLock();
public void sms(){
lock.lock();
try {
System.out.println(Thread.currentThread().getName()+"--> sms()");
call();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void call(){
lock.lock();
try {
System.out.println(Thread.currentThread().getName()+"--> call()");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
3、自旋锁
注意：是T2在自旋，T1在等待解锁
package com.zkw.JUC并发编程.lock;
import java.util.concurrent.atomic.AtomicReference;
public class SpinLockDemon {
//int 0
//Thread = null;
AtomicReference<Thread> atomicReference = new AtomicReference<>();
//加锁
public void MyLock(){
Thread thread = Thread.currentThread();
System.out.println(Thread.currentThread().getName()+"---> MyLock");
//自旋锁
while (!atomicReference.compareAndSet(null,thread)){
}
}
//解锁
public void MyUnLock(){
Thread thread = Thread.currentThread();
System.out.println(Thread.currentThread().getName()+"---> MyUnLock");
atomicReference.compareAndSet(thread,null);
}
}
package com.zkw.JUC并发编程.lock;
import java.util.concurrent.TimeUnit;
public class TestSpinLock {
public static void main(String[] args) throws InterruptedException {
SpinLockDemon lock = new SpinLockDemon();
new Thread(()->{
lock.MyLock();
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
lock.MyUnLock();
}
},"T1").start();
TimeUnit.SECONDS.sleep(2);
new Thread(()->{
lock.MyLock();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.MyUnLock();
}
},"T2").start();
}
}
4、死锁
package com.zkw.JUC并发编程.lock;
import java.util.concurrent.TimeUnit;
public class DeadLockDemon {
public static void main(String[] args) {
String LockA = "LockA";
String LockB = "LockB";
new Thread(new MyThread(LockA,LockB),"T1").start();
new Thread(new MyThread(LockB,LockA),"T2").start();
}
}
class MyThread implements Runnable{
private String LockA;
private String LockB;
public MyThread(String lockA, String lockB) {
LockA = lockA;
LockB = lockB;
}
@Override
public void run() {
synchronized (LockA){
System.out.println(Thread.currentThread().getName()+" Lock "+LockA+"=>get "+LockB);
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (LockB){
System.out.println(Thread.currentThread().getName()+" Lock "+LockB+"=>get "+LockA);
}
}
}
}
解决问题 在IDEA中鼠标点击
1、使用jps -l定位进程号
2、使用jstack 进程号 查看信息