synchronized的写法
class PCdemo{
public static void main(String[] args) {
//多个线程操作同一资源
Data data = new Data();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-1").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-2").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-3").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-4").start();
}
}
//这是一个资源类,
class Data {
private int num = 0;
//加1
public synchronized void increment() throws InterruptedException {
while(num != 0){
this.wait();
}
num++;
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "加1 操作, num为" + num);
this.notifyAll();
}
//减1
public synchronized void decrement() throws InterruptedException {
while(num == 0){
this.wait();
}
num--;
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "减1 操作, num为" + num);
this.notifyAll();
}
}
结果:
这里需要注意一个概念: 虚假唤醒,就是说线程被唤醒了, 但不会被通知 如果把资源类Data中的 increment, decrement方法中的while 换为: if, 那么运行的时候, 二个线程的结果是正常的, 如果二个以上就会出错,结果为
JUC 版本的 生产者和消费者问题
public class JucPCdemo {
public static void main(String[] args) {
//JUC 版本的 就是来替代 synchronized版本的
DataJ data = new DataJ();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-1").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-2").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-3").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-4").start();
}
}
class DataJ{
private Lock lock = new ReentrantLock();
private Condition condition = lock.newCondition();
private int num = 0;
//加1
public void increment() throws InterruptedException {
//先加锁
lock.lock();
try {
while(num != 0){
condition.await();//这个替代 this.wait()
}
num++;
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "加1 操作, num为" + num);
condition.signalAll();// 这个来替代 this.notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
//释放锁
lock.unlock();
}
}
//减1
public void decrement() throws InterruptedException {
//先加锁
lock.lock();
try {
while(num == 0){
condition.await();//这个替代 this.wait();
}
num--;
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "减1 操作, num为" + num);
condition.signalAll();// 这个来替代 this.notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
//释放锁
lock.unlock();
}
}
}
结果同样是正确的
然而 Condition 更强大的是精确通知和精确唤醒, 之前的运行结果线程之间是随机运行的,如果让线程 1,2,3,4 依次循环有序执行, 就要用到Condition
public class JucPCdemo01 {
public static void main(String[] args) {
//JUC 版本的 就是来替代 synchronized版本的
//4个线程依次循环有序执行, num 初始值为0, 线程1--A, 线程2--B, 线程3--C, 线程4--D
DataC data = new DataC();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.printA();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-1").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.printB();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-2").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.printC();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-3").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.printD();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"thread-4").start();
}
}
class DataC{
private Lock lock = new ReentrantLock();
private Condition condition1 = lock.newCondition();//对应A
private Condition condition2 = lock.newCondition();//对应B
private Condition condition3 = lock.newCondition();//对应C
private Condition condition4 = lock.newCondition();//对应D
private String str = "A";
public void printA() throws InterruptedException {
//先加锁
lock.lock();
try {
while(! "A".equals(str)){
condition1.await();//只要不是 A 就等待
}
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "对应str为" + str);
str = "B";
condition2.signal();//这里指定唤醒 线程2 对应B
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
//释放锁
lock.unlock();
}
}
public void printB() throws InterruptedException {
//先加锁
lock.lock();
try {
while(!"B".equals(str)){
condition2.await();//只要不是B 就等待
}
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "对应str为" + str);
str = "C";
condition3.signal();//这里指定唤醒 线程3 对应C
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
//释放锁
lock.unlock();
}
}
public void printC() throws InterruptedException {
//先加锁
lock.lock();
try {
while(! "C".equals(str)){
condition3.await();//只要不是C 就等待
}
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "对应str为" + str);
str = "D";
condition4.signal();//这里指定唤醒 线程4 对应D
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
//释放锁
lock.unlock();
}
}
public void printD() throws InterruptedException {
//先加锁
lock.lock();
try {
while(! "D".equals(str)){
condition4.await();//只要不是D 就等待
}
System.out.println("当前线程名字:" + Thread.currentThread().getName() + "对应str为" + str);
str = "A";
condition1.signal();//这里指定唤醒 线程1 对应A
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
//释放锁
lock.unlock();
}
}
}
运行结果为;
