一、概念
線程是操作系統中獨立的個體,這些線程如果不通過特殊的手段進行處理,就無法組成一個完整的整體。因此線程通信就稱爲組成一個整體的必須條件之一。當線程之間存在通信,那麼系統之間的交互就會更加強大。在提高CPU使用率的前提下,會使開發人員對線程任務在開發的過程中進行有效的把控和監督。
使用wait/notify實現線程之間的通信。這兩個方法都是Object的類方法。也就是java的所有對象都提供了這兩個方法。
wait/notify必須配合關鍵字synchronize使用
wait方法是釋放鎖,notify方法是不釋放鎖
1.異步通信
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
public class ListAdd2 {
private volatile static List list = new ArrayList();
public void add(){
list.add("bjsxt");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd2 list2 = new ListAdd2();
final Object lock = new Object();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
synchronized (lock) {
System.out.println("t1啓動..");
for(int i = 0; i <10; i++){
list2.add();
System.out.println("當前線程:" + Thread.currentThread().getName() + "添加了一個元素..");
Thread.sleep(500);
if(list2.size() == 5){
System.out.println("已經發出通知..");
lock.notify();
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (lock) {
System.out.println("t2啓動..");
if(list2.size() != 5){
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("當前線程:" + Thread.currentThread().getName() + "收到通知線程停止..");
throw new RuntimeException();
}
}
}, "t2");
t2.start(); // 注意此處,t2線程先啓動
t1.start();
}
}
2.實時通信
public class ListAdd3 {
private volatile static List list = new ArrayList();
final static CountDownLatch countDownLatch = new CountDownLatch(1); // 數字表示發起幾次通知,線程纔會被喚醒,如果爲2,則需要寫兩次通知,如代碼中註釋
public void add(){
list.add("bjsxt");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd3 list2 = new ListAdd3();
final Object lock = new Object();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
// synchronized (lock) {
System.out.println("t1啓動..");
for(int i = 0; i <10; i++){
list2.add();
System.out.println("當前線程:" + Thread.currentThread().getName() + "添加了一個元素..");
Thread.sleep(500);
if(list2.size() == 5){
System.out.println("已經發出通知..");
countDownLatch.countDown();
//countDownLatch.countDown(); // 如果括號中數字爲2,則這裏寫幾次
// lock.notify();
}
}
// }
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
//synchronized (lock) {
System.out.println("t2啓動..");
if(list2.size() != 5){
try {
//lock.wait();
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("當前線程:" + Thread.currentThread().getName() + "收到通知線程停止..");
throw new RuntimeException();
}
// }
}, "t2");
t2.start();
t1.start();
}
}
import java.util.ArrayList;
import java.util.List;
public class ListAdd1 {
private volatile static List list = new ArrayList();
public void add(){
list.add("bjsxt");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd1 list1 = new ListAdd1();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
for(int i = 0; i <10; i++){
list1.add();
System.out.println("當前線程:" + Thread.currentThread().getName() + "添加了一個元素..");
Thread.sleep(500);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
while(true){
if(list1.size() == 5){
System.out.println("當前線程收到通知:" + Thread.currentThread().getName() + " list size = 5 線程停止..");
throw new RuntimeException();
}
}
}
}, "t2");
t1.start();
t2.start();
}
}