我想对机场监视器(试图到达的飞机,试图离开的飞机等)进行编码,但我遇到了一些问题。似乎只有一个线程在工作,其他线程卡在某个地方。有人可以看看这个代码并提供帮助吗?
public class Lotniskowiec {
public int K=5;
public int N = 10;
final Lock lock = new ReentrantLock();
final Condition toStart = lock.newCondition();
final Condition toLand= lock.newCondition();
boolean wantsToStart;
boolean wantsToLand;
int atAirport= 0;
boolean free= true;
private void free_landing_area(){
lock.lock();
if(atAirport< K){
if(wantsToLand){
toLand.signal();
}else toStart.signal();
}
else{
if(wantsToStart){
toStart.signal();
} else if (atAirport< N){
toLand.signal();
}
}
lock.unlock();
}
public void wants_to_start(){
lock.lock();
if(!free){
lock.unlock();
try {
toStart.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
lock.lock();
free=false;
lock.unlock();
}
public void started(){
lock.lock();
atAirport-=1;
free=true;
free_landing_area();
lock.unlock();
}
public void wants_to_land(){
lock.lock();
if(!free|| atAirport==N){
lock.unlock();
try {
toLand.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
lock.lock();
free=false;
lock.unlock();
}
public void landed(){
lock.lock();
atAirport+=1;
free=true;
free_landing_area();
lock.unlock();
}
}
很抱歉变量的名称;)
线程:
public class Samolot implements Runnable{
Random random = new Random();
Lotniskowiec lotniskowiec = new Lotniskowiec();
int id;
public Samolot(int id, Lotniskowiec lotniskowiec){
this.id=id;
this.lotniskowiec=lotniskowiec;
}
@Override
public void run() {
while(true){
try {
Thread.sleep(random.nextInt(1000));
Lotniskowiec.wants_to_land();
System.out.println(id + " chce ladowac");
Thread.sleep(random.nextInt(1000));
Lotniskowiec.landed();
System.out.println(id + " wyladowal");
Thread.sleep(random.nextInt(1000));
Lotniskowiec.wants_to_start();
System.out.println(id + " chce startowac");
Thread.sleep(random.nextInt(1000));
Lotniskowiec.started();
System.out.println(id + " wystartowal");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
起始线程:
Samolot r = new Samolot(1,lotniskowiec);
Thread t = new Thread(r);
t.start();
你的wants_to_land
和wants_to_start
是布尔值,但它们应该是整数。否则,您将如何跟踪有多少架飞机希望降落?
另外,我怀疑在飞机调用的每个方法的开头lock.lock()
并在结束时lock.unlock()
就足够了。在当前代码中,飞机获取锁的次数可能多于释放锁的次数,从而有效地从其他飞机那里窃取锁。
此外,它可能有助于使锁公平。
所以
public static int K = 5;
public static int N = 10;
final static Lock lock = new ReentrantLock(true);
final static Condition toStart = lock.newCondition();
final static Condition toLand = lock.newCondition();
static int wantsToStart = 0;
static int wantsToLand = 0;
static int atAirport = 0;
static boolean free = true;
private static void free_landing_area() {
if (atAirport < K) {
if (wantsToLand > 0) {
toLand.signal();
} else {
toStart.signal();
}
} else {
if (wantsToStart > 0) {
toStart.signal();
} else if (atAirport < N) {
toLand.signal();
}
}
}
public static void wants_to_start() {
lock.lock();
if (!free) {
try {
wantsToStart++;
toStart.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
free = false;
lock.unlock();
}
public static void started() {
lock.lock();
atAirport -= 1;
free = true;
wantsToStart--;
free_landing_area();
lock.unlock();
}
public static void wants_to_land() {
lock.lock();
if (!free || atAirport == N) {
try {
wantsToLand++;
toLand.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
free = false;
lock.unlock();
}
public static void landed() {
lock.lock();
atAirport += 1;
free = true;
wantsToLand--;
free_landing_area();
lock.unlock();
}
最后,我相信你实际上需要在 while 循环中等待(),因为在某些情况下线程可能会被意外唤醒。
等待条件时,允许"虚假唤醒" 一般来说,作为对底层平台的让步而发生 语义学。这对大多数应用程序几乎没有实际影响 程序作为条件应始终在循环中等待, 测试正在等待的状态谓词。
所以上面的代码还没有完全到位。但这并不是让你的线程卡住的原因。
好的,这是线索:其他线程被锁定在toLand.await()语句wants_to_land方法中。toLand.signal() 永远不会发生,因为 if(wantsToLand) 和 if(wantsToStart) 都是错误的(你不会无处改变它)。请考虑刷新同步逻辑,看看是否有帮助。