<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.
Multiple threads can execute <code>once.Do(f)</code> for a particular <code>f</code>,

    EntryComparator(@Nullable Comparator<? super K> keyComparator) {
      this.keyComparator = keyComparator;
    }

    @Override
    @SuppressWarnings("unchecked") // no less safe than putting it in the map!
    public int compare(Entry<K, V> a, Entry<K, V> b) {
      return (keyComparator == null)
          ? ((Comparable) a.getKey()).compareTo(b.getKey())

    EntryComparator(@Nullable Comparator<? super K> keyComparator) {
      this.keyComparator = keyComparator;
    }

    @Override
    @SuppressWarnings("unchecked") // no less safe than putting it in the map!
    public int compare(Entry<K, V> a, Entry<K, V> b) {
      return (keyComparator == null)
          ? ((Comparable) a.getKey()).compareTo(b.getKey())

   * number of elements and whose elements may change over time.
   *
   * <p>This test might fail in GWT because the GWT emulations might count on the input collection
   * not to change during the copy. It is safe to do so in GWT because javascript is
   * single-threaded.
   */
  @GwtIncompatible // GWT is single threaded
  public void testCopyOf_threadSafe() {
    /*

     */
    Throwable failureCause() {
      checkState(
          state == FAILED,
          "failureCause() is only valid if the service has failed, service is %s",
          state);
      // requireNonNull is safe because the constructor requires a non-null cause with state=FAILED.
      return requireNonNull(failure);
    }
  }

     * AOSP grief.
     */
    return new AbstractList<StackTraceElement>() {
      /*
       * The following requireNonNull calls are safe because we use jlaStackTrace() only if
       * lazyStackTraceIsLazy() returns true.
       */
      @Override
      public StackTraceElement get(int n) {
        return (StackTraceElement)

 *       appropriate factory method for details. View collections such as {@link
 *       ImmutableMultiset#elementSet} iterate in the same order as the parent, except as noted.
 *   <li><b>Thread safety.</b> It is safe to access this collection concurrently from multiple
 *       threads.
 *   <li><b>Integrity.</b> This type cannot be subclassed outside this package (which would allow
 *       these guarantees to be violated).
 * </ul>
 *

    private static ClassOwnership detectJvmBehavior() {
      class LocalClass<T> {}
      Class<?> subclass = new LocalClass<String>() {}.getClass();
      // requireNonNull is safe because we're examining a type that's known to have a superclass.
      ParameterizedType parameterizedType =
          requireNonNull((ParameterizedType) subclass.getGenericSuperclass());

	}
	buckets := make([]BucketInfo, 0, len(bi.Value()))
	for _, b := range bi.Value() {
		if b != nil {
			buckets = append(buckets, *b)
		}
	}
	bi.Recycle() // BucketInfo has no internal pointers, so it's safe to recycle.
	return buckets, nil
}

func (client *remotePeerS3Client) HealBucket(ctx context.Context, bucket string, opts madmin.HealOpts) (madmin.HealResultItem, error) {
	conn := client.gridConn()
	if conn == nil {

	} else {
		// An error is already set.
		return
	}
	meta, _ = m.o.updateMetacacheListing(meta, m.rpc)
	*m.meta = meta
}

// getErr will return an error if the listing failed.
// The error is not type safe.
func (m *metaCacheRPC) getErr() error {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.meta.status == scanStateError {
		return errors.New(m.meta.error)
	}
	return nil
}