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// ...
synchronized(m) {  // Synchronize on m, not s
  for(Integer k : s) { /* do something */ }
}

Noncompliant Code Example

This noncompliant example incorrectly uses a ReentrantLock as the lock object.

final Lock lock = new ReentrantLock();
synchronized(lock) { /* do something */ }

Compliant Solution

The proper mechanism to lock in this case is to explicitly use the lock() and unlock() methods provided by the ReentrantLock class.

final Lock lock = new ReentrantLock();
lock.lock();
try {
  // ...
} finally {
  lock.unlock();
}

Risk Assessment

Synchronizing on an incorrect variable can provide a false sense of thread safety and result in nondeterministic behavior.

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\[[API 06|AA. Java References#API 06]\] Class String
\[[Pugh 08|AA. Java References#Pugh 08]\] "Synchronization"
\[[Miller 09|AA. Java References#Miller 09]\] Locking
\[[Tutorials 08|AA. Java References#Tutorials 08]\] [Wrapper Implementations|http://java.sun.com/docs/books/tutorial/collections/implementations/wrapper.html]

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