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This means that an unreleased lock in any thread will stop other threads from acquiring the same lock.

Noncompliant Code Example (checked exception)

This noncompliant code example protects a resource by using a ReentrantLock but on an exceptional condition, fails to release the lock. Control flow transfers to the catch block and the call to unlock() does not execute.

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public void doSomething() {
  final Lock lock = new ReentrantLock();
  lock.lock();
  try {
    // Do something with the protected resource
    // This may cause an exception such as FileNotFoundException
  } catch(FileNotFoundException fnf) {
    // Handle the exception
  } finally {
    lock.unlock();
  }
}

Noncompliant Code Example (unchecked exception)

This noncompliant code example protects the thread-unsafe Date instance using a ReentrantLock. It also needs to catch Throwable to be compliant with EXC06-J. Do not allow exceptions to transmit sensitive information.

class DateHandler {
  private Date date = new Date();
  final Lock lock = new ReentrantLock();

  public void doSomething(String str) {
    try {
      lock.lock();
      String dateString = date.toString();
      if (dateString.equals(str)) {
        // ...
      }
      lock.unlock();
    } catch(Throwable t) {
      // Forward to handler
    }
  }
}

However, because it does not check whether str is null , a runtime exception in this component may prevent the lock from being released.

Compliant Solution

This compliant solution adds a finally block and moves the unlock() call to it.

class DateHandler {
  private Date date = new Date();
  final Lock lock = new ReentrantLock();

  public void doSomething(String str) {
    try {
      lock.lock();
      String dateString = date.toString();
      if (str.equals(dateString)) {
        // ...
      }
    } catch(Throwable t) {
      // Forward to handler
    } finally {
      lock.unlock();
    }
  }
}

Consequently, the lock is released successfully even in the event of a runtime exception.

Compliant Solution

Exceptions

EX1 : Locks associated with the use of the synchronized keyword are automatically released on exceptional conditions such as abnormal thread termination.

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