Programs must not lock on an object of a class that implements either or both of the Lock and Condition interfaces of the java.util.concurrent.locks package. Using the intrinsic locks of these classes is a questionable practice even in cases where the code may appear to function correctly. This problem generally arises when code is refactored from intrinsic locking to the java.util.concurrent dynamic-locking utilities.
Noncompliant Code Example (ReentrantLock Lock Object)
The doSomething() method in this noncompliant code example synchronizes on the intrinsic lock of an instance of ReentrantLock rather than on the reentrant mutual exclusion Lock encapsulated by ReentrantLock.
private final Lock lock = new ReentrantLock();
public void doSomething() {
synchronized(lock) {
// ...
}
}
Compliant Solution (lock() and unlock())
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();
}
}
In the absence of a requirement for the advanced functionality of the java.util.concurrent package's dynamic-locking utilities, it is better to use the Executor framework or 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 because the class can end up with two different locking policies.
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
LCK03-J |
medium |
probable |
medium |
P8 |
L2 |
Bibliography
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