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Instances of classes that implement either or both of the Lock and Condition interfaces of the java.util.concurrent.locks package are known as high-level concurrency objects. Using the intrinsic locks of such objects is a questionable practice even in cases where the code may appear to function correctly. Code that uses the intrinsic lock of a Lock object is likely to interact with code that uses the Lock interface. These two components will believe they are protecting data with the same lock, while they are, in fact, using two distinct locks. As such, the Lock will fail to protect any data.

Consequently, programs that interact with such objects must use only the high-level locking facilities provided by the interfaces; use of the intrinsic locks is prohibited. This problem generally arises when code is refactored from intrinsic locking to the java.util.concurrent dynamic-locking utilities.

Noncompliant Code Example (ReentrantLock

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The doSomething() method in this noncompliant code example synchronizes on the the intrinsic lock of an instance of ReentrantLock instead of rather than on the reentrant mutual exclusion Lock encapsulated by ReentrantLock.

private final Lock lock = new ReentrantLock();

public void doSomething() {
  synchronized(lock) {
    // ... 
  }
}

Similarly, it is inappropriate to lock on an object of a class that implements either the Lock or Condition interface (or both) of package java.util.concurrent.locks. Using intrinsic locks of these classes is a questionable practice even though the code may appear to function correctly. This problem is commonly seen when code is refactored from intrinsic locking to the java.util.concurrent dynamic locking utilities.

Compliant Solution (lock() and unlock())

Instead of using the intrinsic locks of objects that implement the Lock interface, such as ReentrantLock, use the This compliant solution uses the lock() and unlock() methods provided by the Lock interface.

private final Lock lock = new ReentrantLock();

public void doSomething() {
  lock.lock();
  try {
    // ...
  } finally {
    lock.unlock();
  }
}

If there is no In the absence of a requirement for using the advanced functionality of the dynamic locking utilities of package java.util.concurrent, prefer using the Executor framework or other package's dynamic-locking utilities, it is better to use other concurrency primitives such as synchronization and atomic classes.

Risk Assessment

Synchronizing on the intrinsic lock of high-level concurrency utilities can cause nondeterministic behavior resulting from inconsistent locking policies.

Automated Detection

Bibliography

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