public class p {
	static int pressureGauge=0;
	static final int safetyLimit = 20;
    
	public static void main(String[]args) {
		pressure []p1 = new pressure[10];
		for (int i=0; i<10; i++)  {
			p1[i] = new pressure(); 
			p1[i].start();
		} 
          // the 10 threads are now running in parallel
		try{ 
			for (int i=0;i<10;i++) 
					p1[i].join();  // wait for thread to end
		} catch(Exception e){ }

		System.out.println(
			"gauge reads "+pressureGauge+", safe limit is 20");
	}

}


//////////////////////////////////////////////////

class pressure extends Thread {


	void RaisePressure() {
		if (p.pressureGauge < p.safetyLimit-15) {  
			// wait briefly to simulate some calculations
			try{sleep(100);} catch (Exception e){} 
			p.pressureGauge += 15;
		}  else 
               ; // pressure too high -- don't do anything.
	}

	public void run() {
		RaisePressure();
	}

/* one possible fix */  // static synchronized void RaisePressure() { 

/* another possible fix:
    static Object O = new Object();

    void RaisePressure() {
        synchronized(O) { 
          if (p.pressureGauge < p.safetyLimit-15) {
                try{sleep(100);} catch (Exception e){} // delay
                p.pressureGauge += 15;
          }  else ; // pressure too high -- don't add to it.
        }
    } 
***********/





// this example shows what will NOT work
/**********
synchronized void RaisePressure() { 
      if (p.pressureGauge < p.safetyLimit-15) {
            try{sleep(100);} catch (Exception e){} // delay
            p.pressureGauge += 15;
      }  else ; // pressure too high -- don't add to it.
} 
***********/

}