*
     * @param username the username to unlock
     * @return true if account was unlocked, false if not found
     */
    public boolean unlockAccount(String username) {
        AccountAttempts account = accountAttempts.get(username);
        if (account != null) {
            account.reset();
            log.info("Manually unlocked account: {}", username);
            return true;
        }
        return false;
    }

      ArrayList<LockGraphNode> acquiredLockList = requireNonNull(acquiredLocks.get());
      LockGraphNode node = lock.getLockGraphNode();
      // Iterate in reverse because locks are usually locked/unlocked in a
      // LIFO order.
      for (int i = acquiredLockList.size() - 1; i >= 0; i--) {
        if (acquiredLockList.get(i) == node) {
          acquiredLockList.remove(i);
          break;
        }
      }

An unsuccessful call has no synchronizing effect at all.
As far as the memory model is concerned,
<code>l.TryLock</code> (or <code>l.TryRLock</code>)
may be considered to be able to return false
even when the mutex <i>l</i> is unlocked.
</p>

<h3 id="once">Once</h3>

<p>
The <code>sync</code> package provides a safe mechanism for
initialization in the presence of multiple goroutines
through the use of the <code>Once</code> type.