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final class Flag {
  private boolean flag = true;
  private final ReadWriteLock lock = new ReentrantReadWriteLock();
  private final Lock readLock = lock.readLock();
  private final Lock writeLock = lock.writeLock();
  
  public synchronized void toggle() { 
    writeLock.lock();
    try {
      flag ^= true; // Same as flag = !flag;
    } finally {
      writeLock.unlock();
    }
  }

  public boolean getFlag() { 
    readLock.lock();
    try {
      return flag;
    } finally {
      readLock.unlock();
    }
  }
}

Wiki MarkupRead-write locks allow a shared state to be accessed by multiple readers or a single writer but never both. "

Wiki Markup
In practice, read-write locks can improve performance for frequently accessed read-mostly data structures on multiprocessor systems; under other conditions they perform slightly worse than exclusive locks due to their greater complexity

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\[[Goetz 06|AA. Java References#Goetz 06]\].

Profiling the application can determine the suitability of read-write locks.

Compliant Solution (AtomicBoolean)

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