[英]Simple program using Java Monitor
我有这个简单的Java程序,它利用监视器让客户进入登机区。 我想我将wait()和notify()语句放在导致程序死锁的错误位置,但是,我自己无法弄明白。 下面是我写的代码。
public class AdultCouple extends Thread
{
private boolean onRide = false;
private int ID;
AdultCouple(int ID)
{
this.ID = ID;
}
public synchronized void getIn()
{
while (!Main.isDoorOpen)
{
try
{
wait();
}
catch (InterruptedException ex)
{
}
System.out.println("Go through");
}
System.out.println("Couple " + ID + " get in boarding area.");
onRide = true;
Main.peopleInBoardingArea++;
notify();
}
public void run()
{
getIn();
}
}
public class Area extends Thread
{
Area()
{
}
public synchronized void openDoor()
{
while (Main.peopleInBoardingArea != 0)
{
try
{
wait();
}
catch (InterruptedException ex)
{
}
}
System.out.println("Area opens");
Main.isDoorOpen = true;
notifyAll();
}
public synchronized void closeDoor()
{
}
public void run()
{
openDoor();
}
}
public class ParentKid extends Thread
{
private boolean onRide = false;
private int ID;
ParentKid(int ID)
{
this.ID = ID;
}
public synchronized void getIn()
{
while (!Main.isDoorOpen)
{
try
{
wait();
}
catch (InterruptedException ex)
{
}
System.out.println("Go through");
}
System.out.println("Couple " + ID + " get in boarding area.");
onRide = true;
Main.peopleInBoardingArea++;
notify();
}
public void run()
{
getIn();
}
}
public class Main
{
public static boolean isDoorOpen = false;
public static int peopleInBoardingArea = 0;
public static void main(String args[])
{
Thread t3 = new Area();
Thread t1 = new ParentKid(1);
Thread t2 = new AdultCouple(2);
t1.start();
t2.start();
t3.start();
try
{
t1.join();
t2.join();
t3.join();
}
catch (InterruptedException ex)
{
}
}
}
问题是您在不同的对象上同步。 当你写这样的东西
public synchronized foo() {...}
你同步这个对象。 在您的情况下,您在当前线程上同步,这没有任何意义。 您应该在同一个对象上同步。
public class Main {
public static Object lock = new Object();
...
}
public class AdultCouple extends Thread
{
private boolean onRide = false;
private int ID;
AdultCouple(int ID)
{
this.ID = ID;
}
public void getIn()
{
synchronized (Main.lock) {
while (!Main.isDoorOpen) {
try {
Main.lock.wait();
} catch (InterruptedException ex) {
}
System.out.println("Go through");
}
System.out.println("Couple " + ID + " get in boarding area.");
onRide = true;
Main.peopleInBoardingArea++;
Main.lock.notifyAll();
}
}
public void run()
{
getIn();
}
}
public class Area extends Thread
{
Area()
{
}
public void openDoor()
{
synchronized (Main.lock) {
while (Main.peopleInBoardingArea != 0) {
try {
Main.lock.wait();
} catch (InterruptedException ex) {
}
}
System.out.println("Area opens");
Main.isDoorOpen = true;
Main.lock.notifyAll();
}
}
public synchronized void closeDoor()
{
}
public void run()
{
openDoor();
}
}
public class ParentKid extends Thread
{
private boolean onRide = false;
private int ID;
ParentKid(int ID)
{
this.ID = ID;
}
public void getIn()
{
synchronized (Main.lock) {
while (!Main.isDoorOpen) {
try {
Main.lock.wait();
} catch (InterruptedException ex) {
}
System.out.println("Go through");
}
System.out.println("Kid " + ID + " get in boarding area.");
onRide = true;
Main.peopleInBoardingArea++;
Main.lock.notifyAll();
}
}
public void run()
{
getIn();
}
}
也不要使用notify()但使用notifyAll()。 我认为没有理由使用它
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