javaee应用中的多线程死锁

Question

我是JavaEE的新手。我想知道在JavaEE应用层中是否存在一些常见的死锁情况，这是由于使用了Java同步原语-synchronized关键字造成的。如果是，请给出一个例子

Answer 1

来自EJB3.1规范，第21.2.2章。编程限制：

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.

推理也很有趣：

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

Answer 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) {
        }

    }
}

从一个线程调用myMethod1，从另一个线程调用myMethod2，将出现死锁