bool BlockNotStale(const std::shared_ptr<Block>& block)
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_);

  /// Look up a Key in the block cache.
  std::shared_ptr<Block> Lookup(const Key& key) ABSL_LOCKS_EXCLUDED(mu_);

  void MaybeFetch(const Key& key, const std::shared_ptr<Block>& block,
                  TF_Status* status) ABSL_LOCKS_EXCLUDED(mu_);

  /// Trim the block cache to make room for another entry.

		err = errLockNotInitialized
	default:
		err = errors.New(r.Err)
	}
	return ok, err
}

// RLock calls read lock REST API.
func (c *lockRESTClient) RLock(ctx context.Context, args dsync.LockArgs) (reply bool, err error) {
	return c.call(ctx, lockRPCRLock, &args)
}

// Lock calls lock REST API.
func (c *lockRESTClient) Lock(ctx context.Context, args dsync.LockArgs) (reply bool, err error) {
	return c.call(ctx, lockRPCLock, &args)
}

// LockArgs is minimal required values for any dsync compatible lock operation.
type LockArgs struct {
	// Unique ID of lock/unlock request.
	UID string

	// Resources contains single or multiple entries to be locked/unlocked.
	Resources []string

	// Source contains the line number, function and file name of the code
	// on the client node that requested the lock.
	Source string

}

// TryLockedOpenFile - tries a new write lock, functionality
// it is similar to LockedOpenFile with with syscall.LOCK_EX
// mode but along with syscall.LOCK_NB such that the function
// doesn't wait forever but instead returns if it cannot
// acquire a write lock.
func TryLockedOpenFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
	return lockedOpenFile(path, flag, perm, syscall.LOCK_NB)
}

	if responses == nil {
		return nil, errors.New("RequestStream: responses channel is nil")
	}
	m.init = true
	m.respMu.Lock()
	if m.closed {
		m.respMu.Unlock()
		return nil, ErrDisconnected
	}
	m.respWait = responses // Route directly to output.
	m.respMu.Unlock()

	// Try to grab an initial block.
	m.singleResp = false
	m.RecvSeq = m.SendSeq // Sync
	if cap(requests) > 0 {

	resp := lockRPCUnlock.NewResponse()
	_, err := l.ll.Unlock(context.Background(), *args)
	// Ignore the Unlock() "reply" return value because if err == nil, "reply" is always true
	// Consequently, if err != nil, reply is always false
	return l.makeResp(resp, err)
}

// RLockHandler - Acquires an RLock.
func (l *lockRESTServer) RLockHandler(args *dsync.LockArgs) (*dsync.LockResp, *grid.RemoteErr) {

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/** Forwarding wrapper around a {@code Lock}. */
@J2ktIncompatible
@ElementTypesAreNonnullByDefault
abstract class ForwardingLock implements Lock {
  abstract Lock delegate();

  @Override
  public void lock() {
    delegate().lock();
  }

  @Override
  public void lockInterruptibly() throws InterruptedException {

	defer func() {
		if unlockOnDefer {
			nsUnlocker()
		}
	}()

	// Acquire lock
	if !opts.NoLock {
		lock := z.NewNSLock(bucket, object)
		lkctx, err := lock.GetRLock(ctx, globalOperationTimeout)
		if err != nil {
			return nil, err
		}
		ctx = lkctx.Context()
		nsUnlocker = func() { lock.RUnlock(lkctx) }
		unlockOnDefer = true
	}

	checkPrecondFn := opts.CheckPrecondFn

### Locks

We have 3 different things that we synchronize on.

#### Http2Connection

This lock guards internal state of each connection. This lock is never held for blocking operations. That means that we acquire the lock, read or write a few fields and release the lock. No I/O and no application-layer callbacks.

#### Http2Stream

   * be removed from the execution schedule.
   */
  fun cancelAll() {
    lock.assertNotHeld()

    taskRunner.lock.withLock {
      if (cancelAllAndDecide()) {
        taskRunner.kickCoordinator(this)
      }
    }
  }

  fun shutdown() {
    lock.assertNotHeld()

    taskRunner.lock.withLock {
      shutdown = true
      if (cancelAllAndDecide()) {