Java、多线程和 Raspberry Pi

Question

所以我的多线程部分工作。当我编译后第一次运行程序时，它只运行 3 个线程中的 1 个或 2 个。然后立即再次运行它，它运行得非常好，所有线程都已激活并运行。我想不出为什么所有线程不会在第一次执行 java 类时运行，然后在第一个线程终止后开始第二次执行该类的任何原因。

我在 Raspberry Pi 2 上使用 Pi4j。我需要代码第一次就能正常运行，因为我试图在 Pi 启动时运行它。

这是我开始线程的地方。

public class Doors {
public static void main(String[] args) {        
    Thread door1 = new Thread(new DoorSwitch(0));
    door1.start();
    Thread door2 = new Thread(new DoorSwitch(1));
    door2.start();
    Thread door3 = new Thread(new DoorSwitch(2));
    door3.start();
}

这就是线程正在运行的内容。线程正在传递我所说的门的值。

public class DoorSwitch implements Runnable{    
int p;
int doorID;
int tempPin;
static DBConnection db = new DBConnection();//create a new object of database connection class
public DoorSwitch(int currPin){
p = currPin;
    doorID = (p + 1);
}
public void run()
{
    try{
        final GpioController gpio = GpioFactory.getInstance();
        final GpioPinDigitalInput[] gpPins = {
                 gpio.provisionDigitalInputPin(RaspiPin.GPIO_28, PinPullResistance.PULL_UP),
                 gpio.provisionDigitalInputPin(RaspiPin.GPIO_29, PinPullResistance.PULL_UP),
                 gpio.provisionDigitalInputPin(RaspiPin.GPIO_27, PinPullResistance.PULL_UP),
         };
        for (int i=1; i<gpPins.length; i++){
            if(p == i){
                tempPin = p;
            }
        }
        final GpioPinDigitalInput door = gpPins[tempPin];
        door.addListener(new GpioPinListenerDigital() {
            @Override
            public void handleGpioPinDigitalStateChangeEvent(GpioPinDigitalStateChangeEvent event) {
                if(event.getState() == PinState.HIGH){
                    try{
                        db.dbConnection();
                        System.out.println(doorID);
                        System.out.println("Door Open! " + p);
                        String update = "UPDATE `door` SET `status`=" + 1 + " WHERE `id`="+ doorID +";";
                        db.getStatement().executeUpdate(update);
                        String log = "INSERT INTO `door_log` (`door_id`, `status`) VALUES ("+ doorID + ",1);";
                        db.getStatement().executeUpdate(log);
                    } catch (SQLException | ClassNotFoundException | InstantiationException | IllegalAccessException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    }
                }
                if(event.getState() == PinState.LOW){
                    try{
                        db.dbConnection();
                        System.out.println(doorID);
                        System.out.println("                Door Closed! " + p);
                        String update = "UPDATE `door` SET `status`=" + 0 + " WHERE `id`="+ doorID +";";
                        db.getStatement().executeUpdate(update);
                        String log = "INSERT INTO `door_log` (`door_id`, `status`) VALUES ("+ doorID + ",0);";
                        db.getStatement().executeUpdate(log);
                    } catch (SQLException | ClassNotFoundException | InstantiationException | IllegalAccessException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    }
                }
                //System.out.println(" --> GPIO PIN STATE CHANGE: " + event.getPin() + " = " + event.getState());
            } 
        });
        while(true) {
            Thread.sleep(500);
        }

        // stop all GPIO activity/threads by shutting down the GPIO controller
        // (this method will forcefully shutdown all GPIO monitoring threads and scheduled tasks)
        // gpio.shutdown();   <--- implement this method call if you wish to terminate the Pi4J GPIO controller
    }catch(Exception e){

    }

}

任何帮助将不胜感激。 谢谢

Answer 1

检查db:共享，使用时不 protected ，并且在每个线程中创建。

结果可能是不可预测的。

我建议:

1 添加此

 static final Object db_sync=new Object();

2 仅初始化一次db，并在DoorSwitch的构造函数中调用它

static DBConnection db=null;

static db_initialize()
{

synchronized(db_sync)
 {
 if (db==null) 
    db = new DBConnection();//create a new object of database connection class
  }

}

3 Surround db的使用

synchronized(db_sync)
 {
  // Do what you want with db
  }