实现司机售票员线程同步模式，比较简单，通俗易懂。
售票员活动：关闭车门
司机的活动：启动车子
司机的活动：正常行驶；售票员活动：售票
司机的活动：到站停车；
售票员活动：打开车门；
pv操作实现
driver(){
while(true){
P(driver);
start();
driving();
stop();
V(Seller);
}
}
seller(){
while(true){
close(door);
V(Driver);
sell();
P(Seller);
open(door);
}
}
很容易看出上述存在死锁，因为如果seller执行完V(Driver)之后Driver还没有执行到P(Driver)，那么当Driver执行到P(Driver)之后则会挂起，而Seller到了P(Seller)之后也同样会挂起，因此死锁产生。
死锁产生的原因是V操作的信号被忽略了。因此只要保持住该信号就可以唤醒Driver。因此java代码对其的改进如下所示：
package concurrency;
import java.security.interfaces.DSAKey;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class DriverAndSeller {
Object driver = new Object();
Object seller = new Object();
int driverNotify = 0;
int sellerNotify = 0;
class Driver implements Runnable{
public void run(){
Random random = new Random(47);
while(true){
try{
synchronized (driver) {
if(driverNotify==0)
driver.wait();
driverNotify--;
}
System.out.println("[Driver]: Starting...");
Thread.sleep(random.nextInt(1000)+1000);
System.out.println("[Driver]: Runing...");
Thread.sleep(random.nextInt(6000));
System.out.println("[Driver]: Stop...");
synchronized (seller) {
sellerNotify++;
seller.notify();
}
}catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
class Seller implements Runnable{
public void run(){
Random random = new Random(47);
while(true){
try{
System.out.println("[Seller]: Closing door...");
synchronized (driver) {
driverNotify++;
driver.notify();
}
Thread.sleep(random.nextInt(1000)+500);
System.out.println("[Seller]: Selling tickets...");
Thread.sleep(random.nextInt(1000)+5000);
synchronized (seller) {
if(sellerNotify==0)
seller.wait();
sellerNotify--;
}
System.out.println("[Seller]: Opening door...");
Thread.sleep(random.nextInt(300)+300);
}catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
public static void main(String[] args){
DriverAndSeller das = new DriverAndSeller();
ExecutorService es = Executors.newFixedThreadPool(2);
es.execute(das.new Driver());
es.execute(das.new Seller());
}
}
所得的结果是：
[Seller]: Closing door... [Driver]: Starting... [Seller]: Selling tickets... [Driver]: Runing... [Driver]: Stop... [Seller]: Opening door... [Seller]: Closing door... [Driver]: Starting... [Seller]: Selling tickets... [Driver]: Runing... [Driver]: Stop... [Seller]: Opening door... [Seller]: Closing door... [Driver]: Starting... [Seller]: Selling tickets... [Driver]: Runing... [Driver]: Stop... [Seller]: Opening door... [Seller]: Closing door... [Driver]: Starting... [Seller]: Selling tickets...