Thread deadlock in Java EE application

问题

I am a newbie to Java EE. I wonder if there are some common deadlock cases in Java EE application layer, resulting from using Java synchronization primitive - synchronized keyword. If yes, could help give an example?

回答1:

From the EJB 3.1 spec, Chapter 21.2.2. Programming Restrictions:

An enterprise bean must not use thread synchronization primitives to synchronize execution of multiple instances, except if it is a Singleton session bean with bean-managed concurrency.

And the reasoning is also interesting:

Synchronization would not work if the EJB container distributed enterprise bean’s instances across multiple JVMs.

回答2:

public void myMethod1() throws Exception {
    synchronized (MyClass.class) {

        Thread.sleep(10*1000);

        synchronized (MyClass2.class) {
        }
    }
}

public void myMethod2() throws Exception {    
    synchronized (MyClass2.class) {

        Thread.sleep(10*1000);

        synchronized (MyClass1.class) {
        }

    }
}

Call myMethod1 from one thread and myMethod2 from other thread and you will get a deadlock.

来源：https://stackoverflow.com/questions/3793135/thread-deadlock-in-java-ee-application