執行緒併發問題和執行緒的休眠
阿新 • • 發佈：2019-02-17
1、併發安全性問題
網際網路的專案中存在這大量的併發案例，如賣火車票，電商網站等
範例：火車票有100張票，4個視窗同時賣票
1）採用繼承Thread來實現
package com.cn.tickets; /** * 賣票視窗 * @author Administrator * */ public class SaleTicket extends Thread { private String name; public SaleTicket(String name) { super(name); } //100張票是共享的資源 private static int tickets = 100; //類屬性,同步鎖（同步鑰匙）物件 private static Object obj = new Object(); @Override public void run() { while(true){ synchronized(obj){ //同步程式碼塊 if(tickets > 0){ try { //休眠時間 Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(this.getName()+"正在賣第："+tickets--+"張票"); }else{ System.out.println("票已經售完"); break; } } } } }
package com.cn.tickets; public class TicketTest { public static void main(String[] args) { SaleTicket st1 = new SaleTicket("視窗1"); SaleTicket st2 = new SaleTicket("視窗2"); SaleTicket st3 = new SaleTicket("視窗3"); SaleTicket st4 = new SaleTicket("視窗4"); st1.start(); st2.start(); st3.start(); st4.start(); } }
2）Runable介面
package com.cn.tickets2; /** * 賣票視窗 * @author Administrator * */ public class SaleTicket implements Runnable { //100張票是共享的資源 private int tickets = 100; //private Object = new Object(); @Override public void run() { while(true){ int i = 0; if(i%2 == 0){ //同步程式碼塊 synchronized(this){ if(tickets > 0){ try { //休眠時間 Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"正在賣第："+tickets--+"張票"); }else{ System.out.println("票已經售完"); break; } } }else{ saleTickets(); } i++; } } /** * 非靜態方法的synchronized鎖是當前物件 */ public synchronized void saleTickets(){ if(tickets > 0){ try { //休眠時間 Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"正在賣第："+tickets--+"張票"); }else{ System.out.println("票已經售完"); } } }
package com.cn.tickets2;
public class TicketTest {
public static void main(String[] args) {
SaleTicket st1 = new SaleTicket();
Thread t1 = new Thread(st1,"視窗1");
Thread t2 = new Thread(st1,"視窗2");
Thread t3 = new Thread(st1,"視窗3");
Thread t4 = new Thread(st1,"視窗4");
t1.start();
t2.start();
t3.start();
t4.start();
}
}
2、執行緒的休眠
執行緒的休眠是很必要的，在做服務端的時候為了減少伺服器的壓力，我們需要休眠，如果休眠是在同步程式碼塊中執行，休眠不會讓出鎖物件
package com.cn.sleep;
/**
* 賣票視窗
* @author Administrator
*
*/
public class SaleTicket implements Runnable {
//100張票是共享的資源
private int tickets = 100;
//private Object = new Object();
@Override
public void run() {
while(true){
//同步程式碼塊
synchronized(this){
if(tickets > 0){
try {
//休眠時間
Thread.sleep(1000);
System.out.println("-------------");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()+"正在賣第："+tickets--+"張票");
}else{
System.out.println("票已經售完");
break;
}
}
}
}
}
package com.cn.sleep;
public class SleepTest {
public static void main(String[] args) {
/**
SleepDemo sd = new SleepDemo();
Thread t = new Thread(sd);
t.start();
*/
SaleTicket st = new SaleTicket();
Thread t1 = new Thread(st,"視窗1");
Thread t2 = new Thread(st,"視窗2");
t1.start();
t2.start();
}
}