Quality Code: Software Testing Principles, Practices, and Patterns

Deadlocks

A deadlock occurs when two or more threads stop execution waiting on each other or a shared resource. While race conditions happen generally through a deficiency of locking, deadlocks occur through incorrect or overzealous locking. Listing 13-4 shows two methods that are destined to eventually deadlock.

Listing 13-4: Two methods likely to deadlock if running on the same object in different threads at the same time

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public class ClassA {  private ClassB that;  public void doSomething() {    synchronized(this) {      synchronized(that) {        // Do the work      }    }  }  public void doSomethingElse() {    synchronized(that) {      synchronized(this) {        // Do other work      }    }  }}

Note the opposite ...