多线程Java如何让线程等待一段时间
停车问题 有n个停车场。在一个停车场上,一次只能有一辆车。如果所有停车场都被占用,那么汽车将等待一段时间,如果仍然没有免费停车场,那么它将离开 它需要使用线程(通过will同步)来解决 这是我的密码: 停车多线程Java如何让线程等待一段时间,java,multithreading,Java,Multithreading,停车问题 有n个停车场。在一个停车场上,一次只能有一辆车。如果所有停车场都被占用,那么汽车将等待一段时间,如果仍然没有免费停车场,那么它将离开 它需要使用线程(通过will同步)来解决 这是我的密码: 停车 class Parking implements Runnable { private Thread thread; private String threadName; static int parkingLots; static { parkingLots = 5; } Pa
class Parking implements Runnable {
private Thread thread;
private String threadName;
static int parkingLots;
static {
parkingLots = 5;
}
Parking(String threadName) {
this.threadName = threadName;
}
public void run() {
if (parkingLots > 0) {
long restTime = (long) (Math.random() * 2000);
try {
parkingLots--;
System.out.println("Car " + threadName + " stands in the parking lot");
Thread.sleep(restTime);
} catch (InterruptedException e) {
}
parkingLots++;
System.out.println("Car " + threadName + " has left parking, it stood there" + ((double)restTime / (double)1000) + " s");
} else
System.out.println("Car " + threadName + " has left parking");
}
public void start() {
if (thread == null) {
thread = new Thread(this, threadName);
thread.start();
}
}
}
Main
public class Main {
public static void main(String[] args) {
ArrayList<Parking> parking = new ArrayList<Parking>();
for (int i = 0; i < 15; i++) {
parking.add(new Parking(String.valueOf(i + 1)));
}
for (Parking i: parking) {
i.start();
}
}
}
但我得到的(当有2个停车场和4辆车时):所有第一辆车(1和2)都停在停车场,其他车(3和4)都离开了,因为没有免费停车场。即使有15辆车,他们还是进不去
那么,我怎样才能让汽车在离开前等待一段时间呢?如果有免费停车场,他们会去那里,否则他们会离开停车场。修改了你的代码,看看这是否有效
public class Parking implements Runnable {
private Thread thread;
private String threadName;
static int parkingLots;
static {
parkingLots = 5;
}
Parking(String threadName) {
this.threadName = threadName;
}
public void run() {
long restTime = (long) (Math.random() * 2000);
if (parkingLots > 0) {
checkparking();
} else {
try {
System.out.println("Car " + threadName + " is waiting");
Thread.sleep(restTime);
System.out.println("Car " + threadName + " is checking for free parkinglot");
checkparking();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void checkparking() {
if (parkingLots > 0) {
long restTime = (long) (Math.random() * 2000);
try {
parkingLots--;
System.out.println("Car " + threadName + " stands in the parking lot");
Thread.sleep(restTime);
} catch (InterruptedException e) {
}
parkingLots++;
System.out.println(
"Car " + threadName + " has left parking, it stood there" + ((double) restTime / (double) 1000) + " s");
} else {
System.out.println(
"Car " + threadName + " has left since there is no parking space");
}
}
public void start() {
if (thread == null) {
thread = new Thread(this, threadName);
thread.start();
}
}
}
公共班机{
public static void main(String[] args) {
ArrayList<Parking> parking = new ArrayList<Parking>();
for (int i = 0; i < 15; i++) {
parking.add(new Parking(String.valueOf(i + 1)));
}
for (Parking i: parking) {
i.start();
}
}
}
您没有使用和同步,您的类不应该实现Runnable,并且您使用的语义不正确 例如,启动后汽车不能停车/离开,多线程是指多个线程同时访问某个对象,而不会导致不一致的状态,在您的情况下,您基本上只是创建线程并执行某些操作 您的结构应该是这样的:
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Parking {
private final Lock monitor = new ReentrantLock();
private final Condition lotAvailable = monitor.newCondition();
private List<Car> parkedCars = new ArrayList<>();
private final int maxCapacity;
private int occupied;
public Parking(int maxCapacity) {
this.maxCapacity = maxCapacity;
}
private boolean tryPark(Car car, int maxWaitingMillis) throws InterruptedException{
try {
monitor.lock();
if(occupied >= maxCapacity){
long nanos = lotAvailable.awaitNanos(maxWaitingMillis);
while (occupied >= maxCapacity) {
if (nanos <= 0L)
return false;
nanos = lotAvailable.awaitNanos(nanos);
}
++occupied;
parkedCars.add(car);
return true;
}
++occupied;
parkedCars.add(car);
return true;
}catch (InterruptedException ie){
System.out.println(ie.getMessage());
throw ie;
}finally {
monitor.unlock();
}
}
private void leave(Car car){
try {
monitor.lock();
if(parkedCars.remove(car)) {
--occupied;
lotAvailable.signal();
}
}catch (Exception e){
System.out.println(e.getMessage());
}finally {
monitor.unlock();
}
}
}
import java.util.ArrayList;
导入java.util.List;
导入java.util.concurrent.locks.Condition;
导入java.util.concurrent.locks.Lock;
导入java.util.concurrent.locks.ReentrantLock;
公共停车场{
私有最终锁定监视器=新的ReentrantLock();
私有最终条件lotAvailable=monitor.newCondition();
私人列表parkedCars=new ArrayList();
私人最终int最大容量;
私人住宅;
公共停车场(国际最大容量){
this.maxCapacity=maxCapacity;
}
私有布尔tryPark(Car-Car,int-maxWaitingMillis)抛出中断异常{
试一试{
monitor.lock();
如果(占用>=最大容量){
long nanos=LOT可用。等待nanos(最大等待毫秒);
同时(占用>=最大容量){
如果(Nano如果你没有使用同步,你应该使用一个锁对象和一些条件变量以正确的方式实现它,这段代码需要以正确的方式进行一些严重的重构。不要将线程
放在可运行的
中。它应该是另一种方式。将主类视为协调器;it将管理ParkingLot
和Car
类型的线程和实例化细节,每个类型都有一个Runnable#run
方法。
Car 2 stands in the parking lot
Car 1 stands in the parking lot
Car 7 is waiting
Car 5 stands in the parking lot
Car 3 stands in the parking lot
Car 6 is waiting
Car 4 stands in the parking lot
Car 9 is waiting
Car 8 is waiting
Car 10 is waiting
Car 11 is waiting
Car 12 is waiting
Car 13 is waiting
Car 14 is waiting
Car 15 is waiting
Car 4 has left parking, it stood there0.049 s
Car 14 is checking for free parkinglot
Car 14 stands in the parking lot
Car 5 has left parking, it stood there0.366 s
Car 2 has left parking, it stood there0.461 s
Car 12 is checking for free parkinglot
Car 12 stands in the parking lot
Car 15 is checking for free parkinglot
Car 15 stands in the parking lot
Car 1 has left parking, it stood there0.882 s
Car 9 is checking for free parkinglot
Car 9 stands in the parking lot
Car 10 is checking for free parkinglot
Car 10 has left since there is no parking space
Car 3 has left parking, it stood there1.014 s
Car 13 is checking for free parkinglot
Car 13 stands in the parking lot
Car 15 has left parking, it stood there0.937 s
Car 6 is checking for free parkinglot
Car 6 stands in the parking lot
Car 11 is checking for free parkinglot
Car 11 has left since there is no parking space
Car 13 has left parking, it stood there0.344 s
Car 7 is checking for free parkinglot
Car 7 stands in the parking lot
Car 8 is checking for free parkinglot
Car 8 has left since there is no parking space
Car 7 has left parking, it stood there0.054 s
Car 14 has left parking, it stood there1.731 s
Car 9 has left parking, it stood there1.359 s
Car 12 has left parking, it stood there1.877 s
Car 6 has left parking, it stood there1.787 s
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Parking {
private final Lock monitor = new ReentrantLock();
private final Condition lotAvailable = monitor.newCondition();
private List<Car> parkedCars = new ArrayList<>();
private final int maxCapacity;
private int occupied;
public Parking(int maxCapacity) {
this.maxCapacity = maxCapacity;
}
private boolean tryPark(Car car, int maxWaitingMillis) throws InterruptedException{
try {
monitor.lock();
if(occupied >= maxCapacity){
long nanos = lotAvailable.awaitNanos(maxWaitingMillis);
while (occupied >= maxCapacity) {
if (nanos <= 0L)
return false;
nanos = lotAvailable.awaitNanos(nanos);
}
++occupied;
parkedCars.add(car);
return true;
}
++occupied;
parkedCars.add(car);
return true;
}catch (InterruptedException ie){
System.out.println(ie.getMessage());
throw ie;
}finally {
monitor.unlock();
}
}
private void leave(Car car){
try {
monitor.lock();
if(parkedCars.remove(car)) {
--occupied;
lotAvailable.signal();
}
}catch (Exception e){
System.out.println(e.getMessage());
}finally {
monitor.unlock();
}
}
}