Classic pen questions: a simple implementation example of a deadlock

Package com.gaopeng.multithread; 

/ ** 
   * achieve a simple example of deadlock 
 * 
 * @author gaopeng 
 * 
 * / 
public  class DeadLockTest { 

    // Create a Resource 
    Private  static Object resourceA = new new Object ();
     Private  static Object ResourceB = new new Object (); 

    public  static  void main (String [] args) {
         // create a thread A 
        the thread ThreadA = new new the thread ( new new the Runnable () { 

            @Override 
            public  void run() {
                // 获取resourceA共享资源的监视器锁
                synchronized (resourceA) {
                    System.out.println(Thread.currentThread() + " get ResourceA");

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                    System.out.println(Thread.currentThread() + " waiting get ResourceB");

                    synchronized (resourceB) {
                        System.out.println(Thread.currentThread() + " get ResourceB"); 
                    } 

                } 
            } 

        }); 

        // Create a thread B 
        the Thread ThreadB = new new the Thread ( new new the Runnable () { 

            @Override 
            public  void RUN () {
                 // Get resourceA shared resource monitor lock 
                the synchronized (ResourceB) { 
                    the System.out .println (Thread.currentThread () + "GET ResourceB is" ); 

                    the try { 
                        the Thread.sleep ( 1000 ); 
                    } the catch (InterruptedException E) { 
                        e.printStackTrace ();
                    }

                    System.out.println(Thread.currentThread() + " waiting get ResourceA");

                    synchronized (resourceA) {
                        System.out.println(Thread.currentThread() + " get ResourceA");
                    }

                }
            }

        });

        // 启动线程
        threadA.start();
        threadB.start();

    }

}

Results are as follows:

 

 

Two threads have been waiting for each other to release the locks held, and then wait until death. . .

The middle of sleep time, in order to prevent a run on the thread acquires the lock of the two objects.

How to avoid deadlock produce it? ? ?

In fact, the cause deadlock and order of application has a lot of resources, use of resources application of the principles of orderliness can avoid deadlock.

Here are several suggestions to:

Avoid a thread simultaneously acquire multiple locks;

Avoid a thread occupy multiple resources simultaneously in the lock, try to ensure that each lock occupies only one resource;

Try using time lock, using lock.tryLock (timeout) instead of using the internal locking mechanism;

For database locks, locking and unlocking must be a database connection, otherwise the situation will appear unsuccessful.